ATP Hydrolysis Activity Research Articles

Structural insights into brassinosteroid export mediated by the Arabidopsis ABC transporter ABCB1

Brassinosteroids (BRs) are steroidal phytohormones indispensable for plant growth, development, and responses to environmental stresses. The export of bioactive BRs to the apoplast is essential for BR signalling initiation, which requires binding of BR molecule to the extracellular domains of the plasma membrane-localized receptor complex. We have previously shown that the Arabidopsis thaliana ATP-binding cassette (ABC) transporter, ABCB19, functions as a BR exporter, and together with its close homologue, ABCB1, positively regulate BR signalling. Here, we demonstrate that ABCB1 is another BR transporter. The ATP hydrolysis activity of ABCB1 was stimulated by bioactive BRs, and its transport activity was confirmed in proteoliposomes and protoplasts. Structures of ABCB1 in substrate-unbound (apo), brassinolide (BL)-bound, and ATP plus BL-bound states were determined. In the BL-bound structure, BL was bound to the hydrophobic cavity formed by the transmembrane domain, and triggered local conformational changes. Together, our data provide additional insights into the ABC transporter-mediated BR export.

Comparative Transcriptome Analysis of Non-Organogenic and Organogenic Tissues of Gaillardia pulchella Revealing Genes Regulating De Novo Shoot Organogenesis

Gaillardia pulchella is an important plant species with pharmacological and ornamental applications. It contains a wide array of phytocompounds which play roles against diseases. In vitro propagation requires callogenesis and differentiation of plant organs, which offers a sustainable, alternative synthesis of compounds. The morphogenetic processes and the underlying mechanisms are, however, known to be under genetic regulation and are little understood. The present study investigated these events by generating transcriptome data, with de novo assembly of sequences to describe shoot morphogenesis molecularly in G. pulchella. The RNA was extracted from the callus of pre- and post-shoot organogenesis time. The callus induction was optimal using leaf segments cultured onto MS medium containing α-naphthalene acetic acid (NAA; 2.0 mg/L) and 6-benzylaminopurine (BAP; 0.5 mg/L) and further exhibited a high shoot regeneration/caulogenesis ability. A total of 68,366 coding sequences were obtained using Illumina150bpPE sequencing and transcriptome assembly. Differences in gene expression patterns were noted in the studied samples, showing opposite morphogenetic responses. Out of 10,108 genes, 5374 (53%) were downregulated, and there were 4734 upregulated genes, representing 47% of the total genes. Through the heatmap, the top 100 up- and downregulating genes’ names were identified and presented. The up- and downregulated genes were identified using the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway. Important pathways, operative during G. pulchella shoot organogenesis, were signal transduction (13.55%), carbohydrate metabolism (8.68%), amino acid metabolism (5.11%), lipid metabolism (3.75%), and energy metabolism (3.39%). The synthesized proteins displayed phosphorylation, defense response, translation, regulation of DNA-templated transcription, carbohydrate metabolic processes, and methylation activities. The genes’ product also exhibited ATP binding, DNA binding, metal ion binding, protein serine/threonine kinase -, ATP hydrolysis activity, RNA binding, protein kinase, heme and GTP binding, and DNA binding transcription factor activity. The most abundant proteins were located in the membrane, nucleus, cytoplasm, ribosome, ribonucleoprotein complex, chloroplast, endoplasmic reticulum membrane, mitochondrion, nucleosome, Golgi membrane, and other organellar membranes. These findings provide information for the concept of molecular triggers, regulating programming, differentiation and reprogramming of cells, and their uses.

The RNA helicase LOS4 regulates pre-mRNA splicing of key genes (EIN2, ERS2, CTR1) in the ethylene signaling pathway.

The Arabidopsis RNA helicase LOS4 plays a key role in regulating pre-mRNA splicing of the genes EIN2, CTR1, and ERS2 in ethylene signaling pathway. The plant hormone ethylene plays diverse roles in plant growth, development, and responses to stress. Ethylene is perceived by the membrane-bound ethylene receptors complex, and then triggers downstream components, such as EIN2, to initiate signal transduction into the nucleus, leading to the activation of ethylene-responsive genes. Over the past decades, substantial information has been accumulated regarding gene cloning, protein-protein interactions, and downstream gene expressions in the ethylene pathway. However, our understanding of mRNA post-transcriptional processing and modification of key genes in the ethylene signaling pathway remains limited. This study aims to provide evidence demonstrating the involvement of the Arabidopsis RNA helicase LOS4 in pre-mRNA splicing of the genes EIN2, CTR1, and ERS2 in ethylene signaling pathway. Various genetic approaches including RNAi gene silencing, CRISPR-Cas9 gene editing, and amino acid mutations were employed in this study. When LOS4 was silenced or knocked down, the ethylene sensitivity of etiolated seedlings was significantly enhanced. Further investigation revealed errors in the EIN2 pre-mRNA splicing when LOS4 was knocked down. In addition, aberrant pre-mRNA splicing was observed in the ERS2 and CTR1 genes in the pathway. Biochemical assays indicated that the los4-2 (E94K) mutant protein exhibited increased ATP binding and enhanced ATP hydrolytic activity. Conversely, the los4-1 (G364R) mutant had reduced substrate RNA binding and lower ATP binding activities. These findings significantly advanced our comprehension of the regulatory functions and molecular mechanisms of RNA helicase in ethylene signaling.

QRICH1 suppresses pediatric T-cell acute lymphoblastic leukemia by inhibiting GRP78

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological malignancy that commonly affects children and adolescents with a poor prognosis. The terminal unfolded protein response (UPR) is an emerging anti-cancer approach, although its role in pediatric T-ALL remains unclear. In our pediatric T-ALL cohort from different centers, a lower QRICH1 expression was found associated with a worse prognosis of pediatric T-ALL. Overexpression of QRICH1 significantly inhibited cell proliferation and stimulated apoptosis of T-ALL both in vitro and in vivo. Upregulation of QRICH1 significantly downregulated 78 KDa glucose-regulated protein (GRP78) and upregulated CHOP, thus activating the terminal UPR. Co-overexpression of GRP78 in T-ALL cells overexpressing QRICH1 partially reverted the inhibited proliferation and stimulated apoptosis. QRICH1 bound to the residues Asp212 and Glu155 of the nucleotide-binding domain (NBD) of GRP78, thereby inhibiting its ATP hydrolysis activity. In addition, QRICH1 was associated with endoplasmic reticulum (ER) stress in T-ALL, and overexpression of QRICH1 reversed drug resistance. Overall, low QRICH1 expression is an independent risk factor for a poor prognosis of pediatric T-ALL. By inhibiting GRP78, QRICH1 suppresses pediatric T-ALL.

Trigonelline prevents high-glucose-induced endothelial-to-mesenchymal transition, oxidative stress, mitochondrial dysfunction, and impaired angiogenic activity in human endothelial EA.hy926 cells

Trigonelline (TRIG) is a natural compound in an alkaloid family found in diverse plants. This compound exerts anti-inflammatory, anti-allergic, anti-oxidative and anti-fibrotic activities in several disease models. However, its beneficial role in endothelial injury, especially induced by diabetes, is unclear. We, therefore, evaluated the effects of TRIG on the cellular proteome of human endothelial (EA.hy926) cells followed by functional validation in high-glucose (HG)-induced endothelial deteriorations. Label-free quantification using nanoLC-ESI-Qq-TOF MS/MS revealed 40 downregulated and 29 upregulated proteins induced by TRIG. Functional enrichment analysis using DAVID and REVIGO tools suggested the involvement of these altered proteins in several biological processes and molecular functions, particularly cell-cell adhesion, ATP metabolic process, cell redox homeostasis, cadherin binding, and ATP hydrolysis activity. Experimental validation showed that HG triggered endothelial-to-mesenchymal transition (EndMT) (as demonstrated by increased spindle index and mesenchymal markers, i.e., fibronectin and vimentin, and decreased endothelial markers, i.e., PECAM-1 and VE-cadherin), increased oxidized proteins, and reduced intracellular ATP, active mitochondria, endothelial tube/mesh formation and VEGF secretion. However, TRIG successfully abolished all these defects induced by HG. These data indicate that TRIG prevents HG-induced EndMT, oxidative stress, mitochondrial dysfunction, and impaired angiogenic activity in human endothelial cells.

Functional diversity in archaeal Hsp60: a molecular mosaic of Group I and Group II chaperonin.

External stress disrupts the balance of protein homeostasis, necessitating the involvement of heat shock proteins (Hsps) in restoring equilibrium andensuring cellular survival. The thermoacidophilic crenarchaeon Sulfolobus acidocaldarius, lacks the conventional Hsp100, Hsp90, and Hsp70, relying solely on a single ATP-dependent Group II chaperonin, Hsp60, comprising three distinct subunits (α, β, and γ) to refold unfolded substrates and maintain protein homeostasis. Hsp60 forms three different complexes, namely Hsp60αβγ, Hsp60αβ, and Hsp60β, at temperatures of 60 °C, 75 °C, and 90 °C, respectively. This study delves into the intricacies of Hsp60 complexes in S. acidocaldarius, uncovering their ability to form oligomeric structures in the presence of ATP. The recognition of substrates by Hsp60 involves hydrophobic interactions, and the subsequent refolding process occurs in an ATP-dependent manner through charge-driven interactions. Furthermore, the Hsp60β homo-oligomeric complex can protect the archaeal and eukaryotic membrane from stress-induced damage. Hsp60 demonstrates nested cooperativity in ATP hydrolysis activity, where MWC-type cooperativity is nested within KNF-type cooperativity. Remarkably, during ATP hydrolysis, Hsp60β, and Hsp60αβ complexes exhibit a mosaic behavior, aligning with characteristics observed in both Group I and Group II chaperonins, adding a layer of complexity to their functionality.

Identification and development of Tetra-ARMS PCR-based screening test for a genetic variant of OLA1 (Tyr254Cys) in the human failing heart.

Obg-like ATPase 1 (OLA1) protein has GTP and ATP hydrolyzing activities and is important for cellular growth and survival. The human OLA1 gene maps to chromosome 2 (locus 2q31.1), near Titin (TTN), which is associated with familial dilated cardiomyopathy (DCM). In this study, we found that expression of OLA1 was significantly downregulated in failing human heart tissue (HF) compared to non-failing hearts (NF). Using the Sanger sequencing method, we characterized the human OLA1 gene and screened for mutations in the OLA1 gene in patients with failing and non-failing hearts. Among failing and non-failing heart patients, we found 15 different mutations in the OLA1 gene, including two transversions, one substitution, one deletion, and eleven transitions. All mutations were intronic except for a non-synonymous 5144A>G, resulting in 254Tyr>Cys in exon 8 of the OLA1 gene. Furthermore, haplotype analysis of these mutations revealed that these single nucleotide polymorphisms (SNPs) are linked to each other, resulting in disease-specific haplotypes. Additionally, to screen the 254Tyr>Cys point mutation, we developed a cost-effective, rapid genetic screening PCR test that can differentiate between homozygous (AA and GG) and heterozygous (A/G) genotypes. Our results demonstrate that this PCR test can effectively screen for OLA1 mutation-associated cardiomyopathy in human patients using easily accessible cells or tissues, such as blood cells. These findings have important implications for the diagnosis and treatment of cardiomyopathy.

Conformations of Bcs1L undergoing ATP hydrolysis suggest a concerted translocation mechanism for folded iron-sulfur protein substrate

The human AAA-ATPase Bcs1L translocates the fully assembled Rieske iron-sulfur protein (ISP) precursor across the mitochondrial inner membrane, enabling respiratory Complex III assembly. Exactly how the folded substrate is bound to and released from Bcs1L has been unclear, and there has been ongoing debate as to whether subunits of Bcs1L act in sequence or in unison hydrolyzing ATP when moving the protein cargo. Here, we captured Bcs1L conformations by cryo-EM during active ATP hydrolysis in the presence or absence of ISP substrate. In contrast to the threading mechanism widely employed by AAA proteins in substrate translocation, subunits of Bcs1L alternate uniformly between ATP and ADP conformations without detectable intermediates that have different, co-existing nucleotide states, indicating that the subunits act in concert. We further show that the ISP can be trapped by Bcs1 when its subunits are all in the ADP-bound state, which we propose to be released in the apo form.

Plastid Molecular Chaperone HSP90C Interacts with the SecA1 Subunit of Sec Translocase for Thylakoid Protein Transport.

The plastid stroma-localized chaperone HSP90C plays a crucial role in maintaining optimal proteostasis within chloroplasts and participates in protein translocation processes. While existing studies have revealed HSP90C's direct interaction with the Sec translocase-dependent client pre-protein PsbO1 and the SecY1 subunit of the thylakoid membrane-bound Sec1 translocase channel system, its direct involvement with the extrinsic homodimeric Sec translocase subunit, SecA1, remains elusive. Employing bimolecular fluorescence complementation (BiFC) assay and other in vitro analyses, we unraveled potential interactions between HSP90C and SecA1. Our investigation revealed dynamic interactions between HSP90C and SecA1 at the thylakoid membrane and stroma. The thylakoid membrane localization of this interaction was contingent upon active HSP90C ATPase activity, whereas their stromal interaction was associated with active SecA1 ATPase activity. Furthermore, we observed a direct interaction between these two proteins by analyzing their ATP hydrolysis activities, and their interaction likely impacts their respective functional cycles. Additionally, using PsbO1, a model Sec translocase client pre-protein, we studied the intricacies of HSP90C's possible involvement in pre-protein translocation via the Sec1 system in chloroplasts. The results suggest a complex nature of the HSP90C-SecA1 interaction, possibly mediated by the Sec client protein. Our studies shed light on the nuanced aspects of HSP90C's engagement in orchestrating pre-protein translocation, and we propose a potential collaborative role of HSP90C with SecA1 in actively facilitating pre-protein transport across the thylakoid membrane.

Insights into the ATP / GTP selectivity of a GTPase, adenylosuccinate synthetase from Leishmania donovani

Many GTPases have been shown to utilize ATP too as the phosphoryl donor. Both GTP and ATP are important molecules in the cellular environments and play multiple and discrete functional role within the cells. In our present study, we showed that one of the purine metabolic enzymes Adenylosuccinate synthetase from Leishmania donovani (LdAdSS) which belongs to the BioD-superfamily of GTPases can also carry out the catalysis by hydrolysing ATP instead of its cognate substrate GTP albeit with less efficiency. Biochemical and biophysical studies indicated its ability to bind to ATP too but at a higher concentration of ATP compared to that of GTP. Sequence analysis and molecular dynamic simulations suggested that residues of the switch loop and the G4-G5 (593SAXD596) connected motif of LdAdSS plays a role in determining the nucleotide specificity. Though the crucial interaction between Asp596 and the nucleotide is broken when ATP is bound, interactions between the Ala594 and the adenine ring of ATP could still hold ATP in the GTP binding site. The results of the present study suggested that though LdAdSS is GTP specific, it still shows ATP hydrolysing activity.

Abstract ND11: Chemoproteomic-enabled discovery of VVD-214, a synthetic lethal allosteric inhibitor of WRN helicase

Abstract WRN helicase is a promising target for treating cancers with microsatellite instability (MSI) due to its essential role in resolving deleterious non-canonical DNA structures that accumulate in cells with faulty mismatch repair mechanisms. Currently, there are no approved drugs directly targeting human DNA or RNA helicases, in part due to the challenging nature of developing potent and selective compounds to this class of proteins. Here we describe the chemical proteomic-enabled discovery of a clinical-stage, covalent allosteric inhibitor of WRN. The clinical lead, VVD-214, covalently engages cysteine 727 of WRN in a nucleotide cooperative manner and inhibits ATP hydrolysis and helicase activity, resulting in widespread double-stranded DNA breaks, nuclear swelling, and cell death in MSI-high, but not microsatellite stable cells. VVD-214 provided robust tumor regression in multiple MSI-high colorectal cancer cell lines and patient derived xenograft models, including models derived from patients progressing on immune checkpoint therapies. VVD-214 was exceptionally well tolerated, and constitutes a promising oral drug candidate for patients with MSI-high cancers. Citation Format: Shota Kikuchi, Piergiorgio Pettazzoni, Kristen A. Baltgalvis, Kelsey N. Lamb, Kent T. Symons, Chu-Chiao Wu, Melissa A. Hoffman, Aaron N. Snead, Xiaodan Song, Thomas Glaza, Jason C. Green, Donald C. Rogness, Betty Lam, Maria E. Rodriguez-Aguirre, David R. Woody, Christie L. Eissler, Socorro Rodiles, Seth M. Negron, Steffen M. Bernard, Eileen Tran, Jonathan Pollock, Ali Tabatabaei, Victor Contreras, Heather N. Williams, Martha K. Pastuszka, John J. Sigler, Markus G. Rudolph, Moritz Classen, Doris Brugger, Christopher Claiborne, Jean-Marc Plancher, Isabel Cuartas, Joan Seoane, Laurence E. Burgess, Robert T. Abraham, David S. Weinstein, Gabriel M. Simon, Matthew P. Patricelli, Todd M. Kinsella. Chemoproteomic-enabled discovery of VVD-214, a synthetic lethal allosteric inhibitor of WRN helicase [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr ND11.

Characterization of the transcriptionally active form of dephosphorylated DctD complexed with dephospho-IIAGlc.

Bacterial enhancer-binding proteins (bEBPs) acquire a transcriptionally active state via phosphorylation. However, transcriptional activation by the dephosphorylated form of bEBP has been observed in DctD, which belongs to Group I bEBP. The formation of a complex between dephosphorylated DctD (d-DctD) and dephosphorylated IIAGlc (d-IIAGlc) is a prerequisite for the transcriptional activity of d-DctD. In the present study, characteristics of the transcriptionally active complex composed of d-IIAGlc and phosphorylation-deficient DctD (DctDD57Q) of Vibrio vulnificus were investigated in its multimeric conformation and DNA-binding ability. DctDD57Q formed a homodimer that could not bind to the DNA. In contrast, when DctDD57Q formed a complex with d-IIAGlc in a 1:1 molar ratio, it produced two conformations: dimer and dodecamer of the complex. Only the dodecameric complex exhibited ATP-hydrolyzing activity and DNA-binding affinity. For successful DNA-binding and transcriptional activation by the dodecameric d-IIAGlc/DctDD57Q complex, extended upstream activator sequences were required, which encompass the nucleotide sequences homologous to the known DctD-binding site and additional nucleotides downstream. This is the first report to demonstrate the molecular characteristics of a dephosphorylated bEBP complexed with another protein to form a transcriptionally active dodecameric complex, which has an affinity for a specific DNA-binding sequence.IMPORTANCEResponse regulators belonging to the bacterial two-component regulatory system activate the transcription initiation of their regulons when they are phosphorylated by cognate sensor kinases and oligomerized to the appropriate multimeric states. Recently, it has been shown that a dephosphorylated response regulator, DctD, could activate transcription in a phosphorylation-independent manner in Vibrio vulnificus. The dephosphorylated DctD activated transcription as efficiently as phosphorylated DctD when it formed a complex with dephosphorylated form of IIAGlc, a component of the glucose-phosphotransferase system. Functional mimicry of this complex with the typical form of transcriptionally active phosphorylated DctD led us to study the molecular characteristics of this heterodimeric complex. Through systematic analyses, it was surprisingly determined that a multimer constituted with 12 complexes gained the ability to hydrolyze ATP and recognize specific upstream activator sequences containing a typical inverted-repeat sequence flanked by distinct nucleotides.

A novel in-frame deletion in KIF5C gene causes infantile onset epilepsy and psychomotor retardation.

Motor proteins, encoded by Kinesin superfamily (KIF) genes, are critical for brain development and plasticity. Increasing studies reported KIF's roles in neurodevelopmental disorders. Here, a 6 years and 3 months-old Chinese boy with markedly symptomatic epilepsy, intellectual disability, brain atrophy, and psychomotor retardation was investigated. His parents and younger sister were phenotypically normal and had no disease-related family history. Whole exome sequencing identified a novel heterozygous in-frame deletion (c.265_267delTCA) in exon 3 of the KIF5C in the proband, resulting in the removal of evolutionarily highly conserved p.Ser90, located in its ATP-binding domain. Sanger sequencing excluded the proband's parents and family members from harboring this variant. The activity of ATP hydrolysis in vitro was significantly reduced as predicted. Immunofluorescence studies showed wild-type KIF5C was widely distributed throughout the cytoplasm, while mutant KIF5C was colocalized with microtubules. The live-cell imaging of the cargo-trafficking assay revealed that mutant KIF5C lost the peroxisome-transporting ability. Drosophila models also confirmed p.Ser90del's essential role in nervous system development. This study emphasized the importance of the KIF5C gene in intracellular cargo-transport as well as germline variants that lead to neurodevelopmental disorders and might enable clinicians for timely and accurate diagnosis and disease management in the future.

Abstract 1703: SMARCA2/4 degraders relieve the differentiation block in AML via changes in chromatin looping and accessibility

Abstract Acute Myeloid Leukemia (AML) is characterized by the unfettered proliferation and poor differentiation of myeloid cells causing reduced survival. The mammalian BAF complexes (also known as SWI/SNF) are important regulators of MYC and the cell cycle. There are three BAF complexes (cBAF, ncBAF and pBAF) that share several subunits. SMARCA2 and 4 are mutually exclusive ATPase subunits within the BAF complexes that use ATP hydrolysis and helicase activity to remodel chromatin via nucleosome sliding and removal. PBRM1 is a SMARCA4 associated factor present in pBAF. The association of SMARCA4 with regulatory elements of transcription factors makes it an intriguing target for AML. To evaluate the role of SMARC2/4 in AML, we analyzed RNA transcripts from highly purified primary AML initiating populations and control samples. Sorted leukemia stem cells (Lin-ve, CD34+, CD38-) overexpressed SMARCA2/4 when compared to healthy cells. A novel and highly selective SMARCA2/4 and PBRM1 PROTAC degrading agent AU-15330 was used to investigate the therapeutic effectiveness of targeting BAF complexes as well as the role of SMARCA2/4 in leukemic pathogenesis. Our data demonstrate that AU-15330 effectively degrades SMARCA2/4 and PBRM1 in human leukemia cell lines with varying mutational profiles; MV4-11 was the most sensitive cell line. When evaluating healthy CD34+ HSPCs as well as patient derived AML cells in colony assays, AU-15330 treatment increased differentiation in patient AML samples with minimal effects on healthy CD34+ cells. A xenograft of patient derived AML cells in irradiated mice was performed to determine the requirement of SMARCA2/4 in leukemia stem cell maintenance. Mice treated with AU-15330 had greater myeloid differentiation, fewer human cells in their bone marrows and reduced leukemia stem cell activity, seen in secondary transplants. To understand the underlying mechanism of how SMARCA2/4 and PBRM1 promote leukemic pathogenesis, we used a multi-omic analysis of transcription and chromatin dynamics in MV4-11 cells: ATAC-seq and RNA-seq identified downregulated genes with decreased accessibility, PRO-seq determined early transcriptional changes and HiChIP showed changes in enhancer promoter loops with SMARC2/4 degradation. Several leukemia related transcription factors as well as inflammatory genes were identified from these analyses as possible targets of the BAF complexes in the context of AML. Finally, to determine the effect of SMARCA2/4 degradation on pBAF association with chromatin, single cell imaging was performed of U2OS cells with HALO-tagged PBRM1 treated with the degrader or DMSO. pBAF in the degrader treated cells improved engagement with target chromatin however, a decrease in the stability of the complex binding to the nucleosome when compared to DMSO treated cells was shown. Taken together, these studies will determine the role of SMARCA2/4 in leukemia disease. Citation Format: Sarah Aminov, Kith Pradhan, Srabani Sahu, Shanisha Gordon-Mitchell, Emma Rabinovich, Ariel Fromowitz, Joyeeta Chakraborty, Srinivas Aluri, Rongbao Zhao, Nayem Haque, Milagros Carbajal, Aditi Shastri, Ulrich Steidl, Susanta Samajdarr, Akhil Kumar, Murali Ramachandra, Robert A. Coleman, Kristy Stengel, Amit K. Verma. SMARCA2/4 degraders relieve the differentiation block in AML via changes in chromatin looping and accessibility [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1703.

Structure and function of the Arabidopsis ABC transporter ABCB19 in brassinosteroid export.

Brassinosteroids are steroidal phytohormones that regulate plant development and physiology, including adaptation to environmental stresses. Brassinosteroids are synthesized in the cell interior but bind receptors at the cell surface, necessitating a yet to be identified export mechanism. Here, we show that a member of the ATP-binding cassette (ABC) transporter superfamily, ABCB19, functions as a brassinosteroid exporter. We present its structure in both the substrate-unbound and the brassinosteroid-bound states. Bioactive brassinosteroids are potent activators of ABCB19 ATP hydrolysis activity, and transport assays showed that ABCB19 transports brassinosteroids. In Arabidopsis thaliana, ABCB19 and its close homolog, ABCB1, positively regulate brassinosteroid responses. Our results uncover an elusive export mechanism for bioactive brassinosteroids that is tightly coordinated with brassinosteroid signaling.

Engineering of IF1 -susceptive bacterial F1 -ATPase.

IF1 , an inhibitor protein of mitochondrial ATP synthase, suppresses ATP hydrolytic activity of F1 . One of the unique features of IF1 is the selective inhibition in mitochondrial F1 (MF1 ); it inhibits catalysis of MF1 but does not affect F1 with bacterial origin despite high sequence homology between MF1 and bacterial F1 . Here, we aimed to engineer thermophilic Bacillus F1 (TF1 ) to confer the susceptibility to IF1 for elucidating the molecular mechanism of selective inhibition of IF1 . We first examined the IF1 -susceptibility of hybrid F1 s, composed of each subunit originating from bovine MF1 (bMF1 ) or TF1 . It was clearly shown that only the hybrid with the β subunit of mitochondrial origin has the IF1 -susceptibility. Based on structural analysis and sequence alignment of bMF1 and TF1 , the five non-conserved residues on the C-terminus of the β subunit were identified as the candidate responsible for the IF1 -susceptibility. These residues in TF1 were substituted with the bMF1 residues. The resultant mutant TF1 showed evident IF1 -susceptibility. Reversely, we examined the bMF1 mutant with TF1 residues at the corresponding sites, which showed significant suppression of IF1 -susceptibility, confirming the critical role of these residues. We also tested additional three substitutions with bMF1 residues in α and γ subunits that further enhanced the IF1 -susceptibility, suggesting the additive role of these residues. We discuss the molecular mechanism by which IF1 specifically recognizes F1 with mitochondrial origin, based on the present result and the structure of F1 -IF1 complex. These findings would help the development of the inhibitors targeting bacterial F1 .

Structural transitions modulate the chaperone activities of Grp94

Hsp90s are ATP-dependent chaperones that collaborate with co-chaperones and Hsp70s to remodel client proteins. Grp94 is the ER Hsp90 homolog essential for folding multiple secretory and membrane proteins. Grp94 interacts with the ER Hsp70, BiP, although the collaboration of the ER chaperones in protein remodeling is not well understood. Grp94 undergoes large-scale conformational changes that are coupled to chaperone activity. Within Grp94, a region called the pre-N domain suppresses ATP hydrolysis and conformational transitions to the active chaperone conformation. In this work, we combined in vivo and in vitro functional assays and structural studies to characterize the chaperone mechanism of Grp94. We show that Grp94 directly collaborates with the BiP chaperone system to fold clients. Grp94's pre-N domain is not necessary for Grp94-client interactions. The folding of some Grp94 clients does not require direct interactions between Grp94 and BiP in vivo, suggesting that the canonical collaboration may not be a general chaperone mechanism for Grp94. The BiP co-chaperone DnaJB11 promotes the interaction between Grp94 and BiP, relieving the pre-N domain suppression of Grp94's ATP hydrolysis activity. In structural studies, we find that ATP binding by Grp94 alters the ATP lid conformation, while BiP binding stabilizes a partially closed Grp94 intermediate. Together, BiP and ATP push Grp94 into the active closed conformation for client folding. We also find that nucleotide binding reduces Grp94's affinity for clients, which is important for productive client folding. Alteration of client affinity by nucleotide binding may be a conserved chaperone mechanism for a subset of ER chaperones.

Characterization of a Structurally Distinct ATP-Dependent Reactivating Factor of Adenosylcobalamin-Dependent Lysine 5,6-Aminomutase.

Several anaerobic bacterial species, including the Gram-negative oral bacterium Fusobacterium nucleatum, ferment lysine to produce butyrate, acetate, and ammonia. The second step of the metabolic pathway─isomerization of β-l-lysine to erythro-3,5-diaminohexanoate─is catalyzed by the adenosylcobalamin (AdoCbl) and pyridoxal 5'-phosphate (PLP)-dependent enzyme, lysine 5,6-aminomutase (5,6-LAM). Similar to other AdoCbl-dependent enzymes, 5,6-LAM undergoes mechanism-based inactivation due to loss of the AdoCbl 5'-deoxyadenosyl moiety and oxidation of the cob(II)alamin intermediate to hydroxocob(III)alamin. Herein, we identified kamB and kamC, two genes responsible for ATP-dependent reactivation of 5,6-LAM. KamB and KamC, which are encoded upstream of the genes corresponding to α and β subunits of 5,6-LAM (kamD and kamE), co-purified following coexpression of the genes in Escherichia coli. KamBC exhibited a basal level of ATP-hydrolyzing activity that was increased 35% in a reaction mixture that facilitated 5,6-LAM turnover with β-l-lysine or d,l-lysine. Ultraviolet-visible (UV-vis) spectroscopic studies performed under anaerobic conditions revealed that KamBC in the presence of ATP/Mg2+ increased the steady-state concentration of the cob(II)alamin intermediate in the presence of excess β-l-lysine. Using a coupled UV-visible spectroscopic assay, we show that KamBC is able to reactivate 5,6-LAM through exchange of the damaged hydroxocob(III)alamin for AdoCbl. KamBC is also specific for 5,6-LAM as it had no effect on the rate of substrate-induced inactivation of the homologue, ornithine 4,5-aminomutase. Based on sequence homology, KamBC is structurally distinct from previously characterized B12 chaperones and reactivases, and correspondingly adds to the list of proteins that have evolved to maintain the cellular activity of B12 enzymes.

Vitamin D3 mitigates type 2 diabetes induced by a high carbohydrate-high fat diet in rats: Role of the purinergic system

This study evaluated the effect of vitamin D3 (VIT D3) supplementation on the enzymatic activities and density of ectonucleoside triphosphate diphosphohydrolase (E-NTPDase), ecto-5-nucleotidase (E-5′-NT), adenosine deaminase (ADA), as well as the density of P2 × 7R, P2Y12R, A1R, A2AR receptors, IL-1β, and oxidative parameters in type 2 diabetic rats. Forty male Wistar rats were fed a high carbohydrate-high fat diet (HCHFD) and received an intraperitoneal injection containing a single dose of streptozotocin (STZ, 35 mg/kg). Animals were divided into four groups: 1) control; 2) control/VIT D3 12 µg/kg; 3) diabetic; and 4) diabetic/VIT D3 12 µg/kg. Results show that VIT D3 reduced blood glucose, ATP hydrolysis, ADA activity, P2Y12R density (platelets), as well as ATP, ADP, and AMP hydrolysis and ADA activity (synaptosomes). Moreover, VIT D3 increased insulin levels and AMP hydrolysis (platelets) and improved antioxidant defense. Therefore, we suggest that VIT D3 treatment modulates hyperglycemia-induced changes via purinergic enzymes and receptor expression, consequently attenuating insulin homeostasis dysregulation in the diabetic state.

Selenite ameliorates the ATP hydrolysis of mitochondrial F1FO-ATPase by changing the redox state of thiol groups and impairs the ADP phosphorylation

Selenite as an inorganic form of selenium can affect the redox state of mitochondria by modifying the thiol groups of cysteines. The F1FO-ATPase has been identified as a mitochondrial target of this compound. Indeed, the bifunctional mechanism of ATP turnover of F1FO-ATPase was differently modified by selenite. The activity of ATP hydrolysis was stimulated, whereas the ADP phosphorylation was inhibited. We ascertain that a possible new protein adduct identified as seleno-dithiol (-S-Se-S-) mercaptoethanol-sensitive caused the activation of F-ATPase activity and the oxidation of free –SH groups in mitochondria. Conversely, the inhibition of ATP synthesis by selenite might be irreversible. The kinetic analysis of the activation mechanism was an uncompetitive mixed type with respect to the ATP substrate. Selenite bound more selectively to the F1FO-ATPase loaded with the substrate by preferentially forming a tertiary (enzyme-ATP-selenite) complex. Otherwise, the selenite was a competitive mixed-type activator with respect to the Mg2+ cofactor. Thus, selenite more specifically bound to the free enzyme forming the complex enzyme-selenite. However, even if the selenite impaired the catalysis of F1FO-ATPase, the mitochondrial permeability transition pore phenomenon was unaffected. Therefore, the reversible energy transduction mechanism of F1FO-ATPase can be oppositely regulated by selenite.