Structure Of Transmembrane Domain Research Articles

Substrate Selection Criteria in Regulated Intramembrane Proteolysis.

Alzheimer's disease is the most common form of dementia encountered in an aging population. Characteristic amyloid deposits of Aβ peptides in the brain are generated through cleavage of amyloid precursor protein (APP) by γ-secretase, an intramembrane protease. Cryo-EM structures of substrate γ-secretase complexes revealed details of the process, but how substrates are recognized and enter the catalytic site is still largely ignored. γ-Secretase cleaves a diverse range of substrate sequences without a common consensus sequence, but strikingly, single point mutations within the transmembrane domain (TMD) of specific substrates may greatly affect cleavage efficiencies. Previously, conformational flexibility was hypothesized to be the main criterion for substrate selection. Here we review the 3D structure and dynamics of several γ-secretase substrate TMDs and compare them with mutants shown to affect the cleavage efficiency. In addition, we present structural and dynamic data on ITGB1, a known nonsubstrate of γ-secretase. A comparison of biophysical details between these TMDs and changes generated by introducing crucial mutations allowed us to unravel common principles that differ between substrates and nonsubstrates. We identified three motifs in the investigated substrates: a highly flexible transmembrane domain, a destabilization of the cleavage region, and a basic signature at the end of the transmembrane helix. None of these appears to be exclusive. While conformational flexibility on its own may increase cleavage efficiency in well-known substrates like APP or Notch1, our data suggest that the three motifs seem to be rather variably combined to determine whether a transmembrane helix is efficiently recognized as a γ-secretase substrate.

Biochemical Properties and Immunogenic Epitopes of Echinococcus granulosus Glutathione S-Transferase as a Vaccine Target: In-Silico Study.

The current in silico study was done to determine the primary biochemical features and immunogenic epitopes of Echinococcus granulosus glutathione S-transferase protein as a potential vaccine candidate. Several web tools were employed to predict physico-chemical properties, antigenicity, allergenicity, solubility, post-translational modification (PTM) sites, subcellular localization, signal peptide, transmembrane domain, secondary and tertiary structure followed by refinement and validations. In addition, B-cell epitopes were predicted and were screened using various web servers, while MHC-binding and CTL epitopes were predicted using IEDB and NetCTL servers, respectively. The protein had 219 residues with a molecular weight of 25.55 kDa and alkaline isoelectric pH (7.5). This protein was stable, thermo-tolerant (aliphatic index: 78.04) and hydrophilic (GRAVY: -0.440). The predicted antigenicity scores were low and the protein was nonallergenic in nature. There were no transmembrane domain and signal peptide in the sequence. Moreover, several B-cell, MHC-binding and CTL epitopes were found in the EgGST protein, which could be further used in multi-epitope vaccines. Further studies are needed on the development of vaccines in vivo using EgGST alone or in combination with other antigens in the future.

Similar structures of influenza M2 transmembrane domain in liposomes and in native E. coli membranes at physiological pH

Similar structures of influenza M2 transmembrane domain in liposomes and in native E. coli membranes at physiological pH

An in silico approach to decipher immunogenic epitopes in Toxoplasma gondii GRA1 and GRA3

Toxoplasma gondii (T. gondii) infection is a worldwide parasitic infection, causing serious threats to humans and livestock. Due to lack of a commercial vaccine, this study aimed at biochemical characterization and identification of immunogenic targets in GRA1 and GRA3 of T. gondii. A number of immunoinformatics web servers were used to predict antigenicity, allergenicity, solubility, physico-chemical properties, subcellular localization, post-translational modifications (PTMs), signal peptide and transmembrane domain, secondary and tertiary structure, along with B- and T-cell epitopes. Good antigenicity scores of 0.4815 (GRA1) and 0.5425 (GRA2) were predicted, without any allergenicity and Ig epitopes. Both proteins were soluble, hydrophilic and thermotolerable molecules. The length and molecular weight (MW) of GRA1 were 190 amino acids and 20.14 kDa, respectively, while the length of GRA3 was 222 residues with a MW of 24.24 kDa. Several antigenic epitopes were found in both protein sequences, some which were capable to induce IFN‐γ and/or IL-4 cytokines. In conclusion, we obtained comprehensive data on potential immunogenic epitopes through computer simulations. These findings serve as a basis for future Toxoplasma vaccine researches.

Cloning, expression, and molecular modification of glycoside hydrolase family 5 genes from Thermoascus aurantiacus.

In this paper, a novel bifunctional cellulase gene cel1 was cloned from Thermoascus aurantiacus by PCR and heterologously expressed in Pichia pastoris GS115. Bioinformatics and other related tools were used to compare the nucleotide homology of target genes, and analyze the signal peptide, transmembrane domain, hydrophilicity, secondary and tertiary structure of proteins. It was concluded that cel1 has similar endoglucanase nucleotide sequences and falls under the GH5 family. It was also found that cel1 has nucleotide sequences similar to glucosidase, which can infer that cel1 may have the properties of glucosidase, indicating that cel1 is multifunctional. At the same time, a part of the nucleotide sequence of the gene was removed to obtain a new gene cel2, and after highly efficient heterologous expression, its specific activity was found to be 2.1 times higher. Its enhancement is related to the exposure of the protein's hollow three-dimensional structure. This paper provides good material for exploring the relationship between the structure of bifunctional enzymes and their functions, which lays a solid foundation for further research and applications, and provides useful insight for gene mining of other novel enzymes.

Structural basis of γ chain family receptor sharing at the membrane level.

Common γ chain (γc) cytokine receptors, including interleukin-2 (IL-2), IL-4, IL-7, IL-9, IL-15, and IL-21 receptors, are activated upon engagement with a common γc receptor (CD132) by concomitant binding of their ectodomains to an interleukin. In this work, we find that direct interactions between the transmembrane domains (TMDs) of both the γc and the interleukin receptors (ILRs) are also required for receptor activation. Moreover, the same γc TMD can specifically recognize multiple ILR TMDs of diverse sequences within the family. Heterodimer structures of γc TMD bound to IL-7 and IL-9 receptor TMDs-determined in a lipid bilayer-like environment by nuclear magnetic resonance spectroscopy-reveal a conserved knob-into-hole mechanism of recognition that mediates receptor sharing within the membrane. Thus, signaling in the γc receptor family requires specific heterotypic interactions of the TMDs.

Permissive Conformations of a Transmembrane Helix Allow Intramembrane Proteolysis by γ-Secretase

The intramembrane protease γ-secretase activates important signaling molecules, such as Notch receptors. It is still unclear, however, how different elements within the primary structure of substrate transmembrane domains (TMDs) contribute to their cleavability. Using a newly developed yeast-based cleavage assay, we identified three crucial regions within the TMDs of the paralogs Notch1 and Notch3 by mutational and gain-of-function approaches. The AAAA or AGAV motifs within the N-terminal half of the TMDs were found to confer strong conformational flexibility to these TMD helices, as determined by mutagenesis coupled to deuterium/hydrogen exchange. Crucial amino acids within the C-terminal half may support substrate docking into the catalytic cleft of presenilin, the enzymatic subunit of γ-secretase. Further, residues close to the C-termini of the TMDs may stabilize a tripartite β-sheet in the substrate/enzyme complex. NMR structures reveal different extents of helix bending as well as an ability to adopt widely differing conformational substates, depending on the sequence of the N-terminal half. The difference in cleavability between Notch1 and Notch3 TMDs is jointly determined by the conformational repertoires of the TMD helices and the sequences of the C-terminal half, as suggested by mutagenesis and building molecular models. In sum, cleavability of a γ-secretase substrate is enabled by different functions of cooperating TMD regions, which deepens our mechanistic understanding of substrate/non-substrate discrimination in intramembrane proteolysis.

Elucidating activation and deactivation dynamics of VEGFR-2 transmembrane domain with coarse-grained molecular dynamics simulations.

The vascular endothelial growth factor receptor 2 (VEGFR-2) is a member of receptor tyrosine kinases (RTKs) and is a dimeric membrane protein that functions as a primary regulator of angiogenesis. As is usual with RTKs, spatial alignment of its transmembrane domain (TMD) is essential toward VEGFR-2 activation. Experimentally, the helix rotations within TMD around their own helical axes are known to participate importantly toward the activation process in VEGFR-2, but the detailed dynamics of the interconversion between the active and inactive TMD forms have not been clearly elucidated at the molecular level. Here, we attempt to elucidate the process by using coarse grained (CG) molecular dynamics (MD) simulations. We observe that inactive dimeric TMD in separation is structurally stable over tens of microseconds, suggesting that TMD itself is passive and does not allow spontaneous signaling of VEGFR-2. By starting from the active conformation, we reveal the mechanism of TMD inactivation through analyzing the CG MD trajectories. We observe that interconversions between a left-handed overlay and a right-handed one are essential for the process of going from an active TMD structure to the inactive form. In addition, our simulations find that the helices can rotate properly when the overlaying structure of the helices interconverts and when the crossing angle of the two helices changes by larger than ~40 degrees. As the activation right after the ligand attachment on VEGFR-2 will take place in the reverse manner of this inactivation process, these structural aspects will also appear importantly for the activation process. The rather large change in helix configuration for activation also explains why VEGFR-2 rarely self-activate and how the activating ligand structurally drive the whole VEGFR-2. This mechanism of TMD activation / inactivation within VEGFR-2 may help in further understanding the overall activation processes of other RTKs.

In silico Analysis of a 29 kDa Echinococcus granulosus Protoscolex Protein (P29) as a Vaccine Candidate against Cystic Echinococcosis.

Vaccination can be a key step in controlling hydatid cyst infection in humans and livestock in endemic areas of the disease. The aim of the Present study was to determine some of the basal biochemical properties followed by prediction and screening of B-cell and MHC-binding epitopes of EgP29 protein in silico. Some of the basic physico-chemical properties along with antigenicity, allergenicity, solubility, post-translational modification (PTM) sites, subcellular localization, signal peptide, transmembrane domain, secondary and tertiary structures followed by refinement and validations were computationally determined for this protein. Also, B-cell epitopes were predicted and screened using various web servers, while MHC-binding and CTL epitopes were predicted using IEDB and NetCTL servers, respectively. The protein is a 238-residue, 27 kDa molecule, with high thermotolerance (aliphatic: 71.81) and hydrophilicity (negative GRAVY). There were several glycosylation and phosphorylation sites in the sequence, without a transmembrane domain and signal peptide. Moreover, several B-cell and MHC-binding epitopes were found in the EgP29 protein, which could be further used in multi-epitope vaccines. In conclusion, results of the present study can be a promising sign for achieving effective approaches to the preparation of a multi-epitope vaccines against echinococcosis. So, it is necessary that the effectiveness of the protein and its epitopes be evaluated in vitro and in vivo.

Exploring the effects of nanodiscs on the conformation of a pentameric ligand-gated ion channel.

Recent advances in image acquisition and processing have unleashed a revolution in biomolecular structure determination via cryoelectron microscopy (cryoEM). Membrane proteins, such as the nicotinic acetylcholine receptor from the pentameric ligand-gated ion channel (pLGIC) superfamily, present challenges in structural studies due to their anisotropic and heterogenous lipid environment. In addition to the overall challenges in determining membrane protein structure, both lipid composition and membrane structure significantly affect the pLGIC conformational landscape, favoring some functional states over others. Nanodiscs, a patch of lipid bilayer surrounded by an amphipathic “scaffold”, are a standard reconstitution system for structure determination by single-particle cryoEM. Using an array of scaffolds, including the original apolipoprotein-derived membrane scaffolding protein, different size nanodiscs can be constructed to facilitate structural and biochemical studies in a quasi-native environment. Recent computational and experimental studies have shown, however, that many lipid properties, including membrane thickness, chain order parameters, and lipid diffusion, show position-dependent alterations upon incorporation into the nanodisc scaffold. To date, however, the effect of nanodisc scaffold and altered lipid properties upon a nanodisc-incorporated protein has not been systematically examined. CryoEM studies from our group have demonstrated that nanodisc scaffold choice affects the determined conformation of the pLGIC, ELIC. These nanodiscs differ in size which may be one factor influencing protein structure and dynamics. Here, we use molecular dynamics to examine how nanodisc size (small, 9 nm; medium, 11 nm; large, 13 nm) alters the transmembrane domain (TMD) structure and dynamics of ELIC, a bacterial pLGIC. Our simulation studies show that 1) the nanodisc construct and channel directly interact and 2) lipid properties are affected in a position-dependent manner leading to altered TMD dynamics. Specifically, dynamics in M4, thought to be responsible for lipid-sensing, are altered to the greatest extent.

How transmembrane helices of type 1 receptors transmit information: prediction of dimers with the Martini 3 coarse grained model

Determination of the structure and dynamics of transmembrane (TM) domains of single-transmembrane receptors is key to understanding their mechanism of signal transduction across the plasma membrane. Although many studies have been performed on isolated soluble extra- and intracellular receptor domains in aqueous solutions, limited knowledge exists on the lipid embedded TM region. In this study, we predict the assembly of alternate configurations of receptor TM domain dimers using the Martini 3 force field for coarse-grain (CG) molecular dynamic simulations.

Clinical, Genetic and Functional Characterization of a Novel AVPR2 Missense Mutation in a Woman with X-Linked Recessive Nephrogenic Diabetes Insipidus.

Nephrogenic diabetes insipidus (NDI) is a rare disorder characterized by renal unresponsiveness to the hormone vasopressin, leading to excretion of large volumes of diluted urine. Mutations in the arginine vasopressin receptor-2 (AVPR2) gene cause congenital NDI and have an X-linked recessive inheritance. The disorder affects almost exclusively male family members, but female carriers occasionally present partial phenotypes due to skewed inactivation of the X-chromosome. Here, we report a rare case of a woman affected with X-linked recessive NDI, presenting an average urinary output of 12 L/day. Clinical and biochemical studies showed incomplete responses to water deprivation and vasopressin stimulation tests. Genetic analyses revealed a novel heterozygous missense mutation (c.493G > C, p.Ala165Pro) in the AVPR2 gene. Using a combination of in-silico protein modeling with human cellular models and molecular phenotyping, we provide functional evidence for phenotypic effects. The mutation destabilizes the helical structure of the AVPR2 transmembrane domains and disrupts its plasma membrane localization and downstream intracellular signaling pathways upon activation with its agonist vasopressin. These defects lead to deficient aquaporin 2 (AQP2) membrane translocation, explaining the inability to concentrate urine in this patient.

Echinococcus granulosus cyclophilin: Immunoinformatics analysis to provide insights into the biochemical properties and immunogenic epitopes

Vaccination is a prominent strategy to confine cystic echinococcosis (CE) in areas of endemicity worldwide. The present study was performed to predict the primary biochemical features and immunogenic epitopes of Echinococcus granulosus cyclophilin protein as a potential vaccine candidate. Some of the basic physico-chemical properties along with antigenicity, allergenicity, solubility, post-translational modification (PTM) sites, subcellular localization, signal peptide, transmembrane domain, secondary and tertiary structures followed by refinement and validations were computationally determined for this protein. Also, B-cell epitopes were predicted and screened using various web servers, while MHC-binding and CTL epitopes were predicted using IEDB and NetCTL servers, respectively. The protein is a 162-residue, 17.35 kDa molecule, with relative thermotolerance (aliphatic: 60.12) and hydrophilicity (negative GRAVY). There were N-glycosylation and phosphorylation sites in the sequence, without a transmembrane domain. Moreover, several B-cell, MHC-binding and CTL epitopes were found in the EgGST protein, which could be further used in multi-epitope vaccines. In conclusion, the protein and its epitopes should be examined in wet lab experiments and in vivo.

Systematic profiling of temperature- and retinal-sensitive rhodopsin variants by deep mutational scanning

Membrane protein variants with diminished conformational stability often exhibit enhanced cellular expression at reduced growth temperatures. The expression of “temperature-sensitive” variants is also typically sensitive to corrector molecules that bind and stabilize the native conformation. There are many examples of temperature-sensitive rhodopsin variants, the misfolding of which is associated with the molecular basis of retinitis pigmentosa. In this work, we employ deep mutational scanning to compare the effects of reduced growth temperature and 9-cis-retinal, an investigational corrector, on the plasma membrane expression of 700 rhodopsin variants in HEK293T cells. We find that the change in expression at reduced growth temperatures correlates with the response to 9-cis-retinal among variants bearing mutations within a hydrophobic transmembrane domain (TM2). The most sensitive variants appear to disrupt a native helical kink within this transmembrane domain. By comparison, mutants that alter the structure of a polar transmembrane domain (TM7) exhibit weaker responses to temperature and retinal that are poorly correlated. Statistical analyses suggest that this observed insensitivity cannot be attributed to a single variable, but likely arises from the composite effects of mutations on the energetics of membrane integration, the stability of the native conformation, and the integrity of the retinal-binding pocket. Finally, we show that the characteristics of purified temperature- and retinal-sensitive variants suggest that the proteostatic effects of retinal may be manifested during translation and cotranslational folding. Together, our findings highlight several biophysical constraints that appear to influence the sensitivity of genetic variants to temperature and small-molecule correctors.

Targeted capture sequencing identifies genetic variations of GRK4 and RDH8 in Han Chinese with essential hypertension in Xinjiang.

Essential hypertension is a common cardiovascular disease with complex etiology, closely related to genetic and environmental factors. The pathogenesis of hypertension involves alteration in vascular resistance caused by sympathetic nervous system (SNS) and renin angiotensin system (RAS). Susceptibility factors of hypertension vary with regions and ethnicities. In this study, we conducted target capture sequencing on 54 genes related to SNS and RAS derived from a collection of Han nationality, consisting of 151 hypertension patients and 65 normal subjects in Xinjiang, China. Six non-synonymous mutations related to hypertension were identified, including GRK4 rs1644731 and RDH8 rs1801058, Mutations are predicted to affect 3D conformation, force field, transmembrane domain and RNA secondary structure of corresponding genes. Based on protein interaction network and pathway enrichment, GRK4 is predicted to participate in hypertension by acting on dopaminergic synapse, together with interacting components. RDH8 is involved in vitamin A (retinol) metabolism and consequent biological processes related to hypertension. Thus, GRK4 and RDH8 may serve as susceptibility genes for hypertension. This finding provides new genetic evidence for elucidating risk factors of hypertension in Han nationality in Xinjiang, which in turn, enriches genetic resource bank of hypertension susceptibility genes.

Detergent-free systems for structural studies of membrane proteins.

Membrane proteins play vital roles in living organisms, serving as targets for most currently prescribed drugs. Membrane protein structural biology aims to provide accurate structural information to understand their mechanisms of action. The advance of membrane protein structural biology has primarily relied on detergent-based methods over the past several decades. However, detergent-based approaches have significant drawbacks because detergents often damage the native protein-lipid interactions, which are often crucial for maintaining the natural structure and function of membrane proteins. Detergent-free methods recently have emerged as alternatives with a great promise, e.g. for high-resolution structure determinations of membrane proteins in their native cell membrane lipid environments. This minireview critically examines the current status of detergent-free methods by a comparative analysis of five groups of membrane protein structures determined using detergent-free and detergent-based methods. This analysis reveals that current detergent-free systems, such as the styrene-maleic acid lipid particles (SMALP), the diisobutyl maleic acid lipid particles (DIBMALP), and the cycloalkane-modified amphiphile polymer (CyclAPol) technologies are not better than detergent-based approaches in terms of maintenance of native cell membrane lipids on the transmembrane domain and high-resolution structure determination. However, another detergent-free technology, the native cell membrane nanoparticles (NCMN) system, demonstrated improved maintenance of native cell membrane lipids with the studied membrane proteins, and produced particles that were suitable for high-resolution structural analysis. The ongoing development of new membrane-active polymers and their optimization will facilitate the maturation of these new detergent-free systems.

A Trimeric Hydrophobic Zipper Mediates the Intramembrane Assembly of SARS-CoV-2 Spike.

The S protein of SARS-CoV-2 is a type I membrane protein that mediates membrane fusion and viral entry. A vast amount of structural information is available for the ectodomain of S, a primary target by the host immune system, but much less is known regarding its transmembrane domain (TMD) and its membrane-proximal regions. Here, we determined the NMR structure of the S protein TMD in bicelles that closely mimic a lipid bilayer. The TMD structure is a transmembrane α-helix (TMH) trimer that assembles spontaneously in a membrane. The trimer structure shows an extensive hydrophobic core along the 3-fold axis that resembles that of a trimeric leucine/isoleucine zipper, but with tetrad, not heptad, repeats. The trimeric core is strong in bicelles, resisting hydrogen–deuterium exchange for weeks. Although highly stable, structural guided mutagenesis identified single mutations that can completely dissociate the TMD trimer. Multiple studies have shown that the membrane anchors of viral fusion proteins can form highly specific oligomers, but the exact function of these oligomers remains unclear. Our findings should guide future experiments to address the above question for SARS coronaviruses.

Fast-Trk(B)ing the mechanism of antidepressants

The mechanism by which antidepressants elicit clinical improvements has proven elusive. In a recent publication in Cell, Casarotto etal. (2021) reveal a surprising direct interaction between antidepressants and TrkB. This link provides an important mechanistic insight into synaptic remodeling that may assist in the design of improved antidepressant therapeutics.

Transmembrane 163 (TMEM163) Protein: A New Member of the Zinc Efflux Transporter Family

A growing body of evidence continues to demonstrate the vital roles that zinc and its transporters play on human health. The mammalian solute carrier 30 (SLC30) family, with ten current members, controls zinc efflux transport in cells. TMEM163, a recently reported zinc transporter, has similar characteristics in both predicted transmembrane domain structure and function to the cation diffusion facilitator (CDF) protein superfamily. This review discusses past and present data indicating that TMEM163 is a zinc binding protein that transports zinc in cells. We provide a brief background on TMEM163’s discovery, transport feature, protein interactome, and similarities, as well as differences, with known SLC30 (ZnT) protein family. We also examine recent reports that implicate TMEM163 directly or indirectly in various human diseases such as Parkinson’s disease, Mucolipidosis type IV and diabetes. Overall, the role of TMEM163 protein in zinc metabolism is beginning to be realized, and based on current evidence, we propose that it is likely a new CDF member belonging to mammalian SLC30 (ZnT) zinc efflux transporter proteins.

Cloning, Spatiotemporal Expression and Prokaryotic Expression of ACC Oxidase Gene (<I>BnACO2</i>) in Ramie

ACC oxidase (ACO) is a key enzyme in ethylene synthesis pathway. This study by rt-pcr with RACE technology get a ACO gene cloning, named  BnACO2 , total length of the gene cDNA sequence is 1 377 bp, the open reading frame of 957 bp, coded 318 amino acid polypeptide, predict its molecular weight and isoelectric point (pl) 36.145 kD and 5.60, respectively, bioinformatics analysis showed that  BnACO2  no encoding protein signal peptide and transmembrane domain structure, subcellular localization in the cytoplasm. The similarity of ACO gene nucleotide sequence and amino acid sequence was more than 82% and 84% respectively. Phylogenetic analysis showed that the ACO gene was closely related to jute and hemp. Real-time fluorescence quantitative PCR analysis showed that  BnACO2  gene was expressed in all parts of ramie, especially in female flower buds. The prokaryotic expression vector PQe- BnACO2  was successfully constructed by double enzyme digestion. At 37°C, 1.0mmol/L IPTG induced PQe- BnACO2  to express the target protein, and the molecular weight of the induced protein was about 36.15kda, which was consistent with the predicted protein size. This lays the foundation for further study on the function of  BnACO2  gene.