Chemical Shift Perturbation Data Research Articles

MELD-Adapt: On-the-Fly Belief Updating in Integrative Molecular Dynamics.

Integrative structural biology synergizes experimental data with computational methods to elucidate the structures and interactions within biomolecules, a task that becomes critical in the absence of high-resolution structural data. A challenging step for integrating the data is knowing the expected accuracy or belief in the dataset. We previously showed that the Modeling Employing Limited Data (MELD) approach succeeds at predicting structures and finding the best interpretation of the data when the initial belief is equal to or slightly lower than the real value. However, the initial belief might be unknown to the user, as it depends on both the technique and the system of study. Here we introduce MELD-Adapt, designed to dynamically evaluate and infer the reliability of input data while at the same time finding the best interpretation of the data and the structures compatible with it. We demonstrate the utility of this method across different systems, particularly emphasizing its capability to correct initial assumptions and identify the correct fraction of data to produce reliable structural models. The approach is tested with two benchmark sets: the folding of 12 proteins with coarse physical insights and the binding of peptides with varying affinities to the extraterminal domain using chemical shift perturbation data. We find that subtle differences in data structure (e.g., locally clustered or globally distributed), starting belief, and force field preferences can have an impact on the predictions, limiting the possibility of a transferable protocol across all systems and data types. Nonetheless, we find a wide range of initial setup conditions that will lead to successful sampling and identification of native states, leading to a robust pipeline. Furthermore, disagreements about how much data is enforced and satisfied rapidly serve to identify incorrect setup conditions.

Integrative Modeling of Protein-Polypeptide Complexes by Bayesian Model Selection using AlphaFold and NMR Chemical Shift Perturbation Data.

Protein-polypeptide interactions, including those involving intrinsically-disordered peptides and intrinsically-disordered regions of protein binding partners, are crucial for many biological functions. However, experimental structure determination of protein-peptide complexes can be challenging. Computational methods, while promising, generally require experimental data for validation and refinement. Here we present CSP_Rank, an integrated modeling approach to determine the structures of protein-peptide complexes. This method combines AlphaFold2 (AF2) enhanced sampling methods with a Bayesian conformational selection process based on experimental Nuclear Magnetic Resonance (NMR) Chemical Shift Perturbation (CSP) data and AF2 confidence metrics. Using a curated dataset of 108 protein-peptide complexes from the Biological Magnetic Resonance Data Bank (BMRB), we observe that while AF2 typically yields models with excellent consistency with experimental CSP data, applying enhanced sampling followed by data-guided conformational selection routinely results in ensembles of structures with improved agreement with NMR observables. For two systems, we cross-validate the CSP-selected models using independently acquired nuclear Overhauser effect (NOE) NMR data and demonstrate how CSP and NMR can be combined using our Bayesian framework for model selection. CSP_Rank is a novel method for integrative modeling of protein-peptide complexes and has broad implications for studies of protein-peptide interactions and aiding in understanding their biological functions.

Hexamethylene amiloride binds the SARS-CoV-2 envelope protein at the protein-lipid interface.

The SARS-CoV-2 envelope (E) protein forms a five-helix bundle in lipid bilayers whose cation-conducting activity is associated with the inflammatory response and respiratory distress symptoms of COVID-19. E channel activity is inhibited by the drug 5-(N,N-hexamethylene) amiloride (HMA). However, the binding site of HMA in E has not been determined. Here we use solid-state NMR to measure distances between HMA and the E transmembrane domain (ETM) in lipid bilayers. 13 C, 15 N-labeled HMA is combined with fluorinated or 13 C-labeled ETM. Conversely, fluorinated HMA is combined with 13 C, 15 N-labeled ETM. These orthogonal isotopic labeling patterns allow us to conduct dipolar recoupling NMR experiments to determine the HMA binding stoichiometry to ETM as well as HMA-protein distances. We find that HMA binds ETM with a stoichiometry of one drug per pentamer. Unexpectedly, the bound HMA is not centrally located within the channel pore, but lies on the lipid-facing surface in the middle of the TM domain. This result suggests that HMA may inhibit the E channel activity by interfering with the gating function of an aromatic network. These distance data are obtained under much lower drug concentrations than in previous chemical shift perturbation data, which showed the largest perturbation for N-terminal residues. This difference suggests that HMA has higher affinity for the protein-lipid interface than the channel pore. These results give insight into the inhibition mechanism of HMA for SARS-CoV-2 E.

Structural Model of the Human BTG2–PABPC1 Complex by Combining Mutagenesis, NMR Chemical Shift Perturbation Data and Molecular Docking

Degradation of cytoplasmic mRNA in eukaryotes involves the shortening and removal of the mRNA poly(A) tail by poly(A)-selective ribonuclease (deadenylase) enzymes. In human cells, BTG2 can stimulate deadenylation of poly(A) bound by cytoplasmic poly(A)-binding protein PABPC1. This involves the concurrent binding by BTG2 of PABPC1 and the Caf1/CNOT7 nuclease subunit of the Ccr4-Not deadenylase complex. To understand in molecular detail how PABPC1 and BTG2 interact, we set out to identify amino acid residues of PABPC1 and BTG2 contributing to the interaction. To this end, we first used algorithms to predict PABPC1 interaction surfaces. Comparison of the predicted interaction surface with known residues involved in the binding to poly(A) resulted in the identification of a putative interaction surface for BTG2. Subsequently, we used pulldown assays to confirm the requirement of PABPC1 residues for the interaction with BTG2. Analysis of RNA-binding by PABPC1 variants indicated that PABPC1 residues required for interaction with BTG2 do not interfere with poly(A) binding. After further defining residues of BTG2 that are required for the interaction with PABPC1, we used information from published NMR chemical shift perturbation experiments to guide docking and generate a structural model of the BTG2-PABPC1 complex. A quaternary poly(A)-PABPC1-BTG2-Caf1/CNOT7 model showed that the 3′ end of poly(A) RNA is directed towards the catalytic centre of Caf1/CNOT7, thereby providing a rationale for enhanced deadenylation by Caf1/CNOT7 in the presence of BTG2 and PABPC1.

Principal component analysis of data from NMR titration experiment of uniformly 15N labeled amyloid beta (1–42) peptide with osmolytes and phenolic compounds

A simple NMR method to analyze the data obtained by NMR titration experiment of amyloid formation inhibitors against uniformly 15N-labeled amyloid-β 1–42 peptide (Aβ(1–42)) was described. By using solution nuclear magnetic resonance (NMR) measurement, the simplest method for monitoring the effects of Aβ fibrilization inhibitors is the NMR chemical shift perturbation (CSP) experiment using 15N-labeled Aβ(1–42). However, the flexible and dynamic nature of Aβ(1–42) monomer may hamper the interpretation of CSP data. Here we introduced principal component analysis (PCA) for visualizing and analyzing NMR data of Aβ(1–42) in the presence of amyloid inhibitors including high concentration osmolytes. We measured 1H–15N 2D spectra of Aβ(1–42) at various temperatures as well as of Aβ(1–42) with several inhibitors, and subjected all the data to PCA (PCA-HSQC). The PCA diagram succeeded in differentiating the various amyloid inhibitors, including epigallocatechin gallate (EGCg), rosmarinic acid (RA) and curcumin (CUR) from high concentration osmolytes. We hypothesized that the CSPs reflected the conformational equilibrium of intrinsically disordered Aβ(1–42) induced by weak inhibitor binding rather than the specific molecular interactions.

Structural insight into the interaction between p53 TAD1 and AIMP2-DX2 by NMR

p53 is the most studied tumor suppressor and a key transcriptional factor, with discrete domains that regulate cellular pathways such as apoptosis, angiogenesis, cell-cycle arrest, DNA repair, and senescence. Previous studies have suggested that AIMP2, and ARS-interacting multifunctional protein 2, promote cell death via the protective interaction with p53 upon DNA damage. Also, oncogenic splicing variant of AIMP2 lacking exon2, AIMP2-DX2, compromises the pro-apoptotic activity and anti-proliferative activities of the AIMP2 by competing with AIMP2 for the binding with p53. However, the molecular mechanism for the interaction of p53 and AIMP2 remains elusive. Using NMR spectroscopy, we studied the structural details of the interaction of transactivation domain 1 (TAD1) of p53 with GST domain of AIMP2, which is also common in AIMP2-DX2. The chemical shift perturbation (CSP) experiments demonstrate that amino acid residues from E17 to E28 of p53, known to bind to MDM2 are also involved in binding to AIMP2-DX2. Structure determination of this region based on the transferred-NOE (trNOE) data revealed that TAD1 of the p53 forms a turn structure with hydrophobic interactions by side chains of F19, L22, W23 and L26, distinct from the structure for MDM2 binding. Also, docking results based on NMR CSP data suggest the binding mode of p53 with AIMP2-DX2 GST domain. These data provide the first structural insight into the binding of the p53 TAD1 on AIMP2 and AIMP2-DX2.

Chemical-Shift Perturbations Reflect Bile Acid Binding to Norovirus Coat Protein: Recognition Comes in Different Flavors.

Bile acids have been reported as important cofactors promoting human and murine norovirus (NoV) infections in cell culture. The underlying mechanisms are not resolved. Through the use of chemical shift perturbation (CSP) NMR experiments, we identified a low‐affinity bile acid binding site of a human GII.4 NoV strain. Long‐timescale MD simulations reveal the formation of a ligand‐accessible binding pocket of flexible shape, allowing the formation of stable viral coat protein–bile acid complexes in agreement with experimental CSP data. CSP NMR experiments also show that this mode of bile acid binding has a minor influence on the binding of histo‐blood group antigens and vice versa. STD NMR experiments probing the binding of bile acids to virus‐like particles of seven different strains suggest that low‐affinity bile acid binding is a common feature of human NoV and should therefore be important for understanding the role of bile acids as cofactors in NoV infection.

Interaction of the tetratricopeptide repeat domain of aryl hydrocarbon receptor–interacting protein–like 1 with the regulatory Pγ subunit of phosphodiesterase 6

Phosphodiesterase-6 (PDE6) is key to both phototransduction and health of rods and cones. Proper folding of PDE6 relies on the chaperone activity of aryl hydrocarbon receptor-interacting protein-like 1 (AIPL1), and mutations in both PDE6 and AIPL1 can cause a severe form of blindness. Although AIPL1 and PDE6 are known to interact via the FK506-binding protein domain of AIPL1, the contribution of the tetratricopeptide repeat (TPR) domain of AIPL1 to its chaperone function is poorly understood. Here, we demonstrate that AIPL1-TPR interacts specifically with the regulatory Pγ subunit of PDE6. Use of NMR chemical shift perturbation (CSP) mapping technique revealed the interface between the C-terminal portion of Pγ and AIPL1-TPR. Our solution of the crystal structure of the AIPL1-TPR domain provided additional information, which together with the CSP data enabled us to generate a model of this interface. Biochemical analysis of chimeric AIPL1-AIP proteins supported this model and also revealed a correlation between the affinity of AIPL1-TPR for Pγ and the ability of Pγ to potentiate the chaperone activity of AIPL1. Based on these results, we present a model of the larger AIPL1-PDE6 complex. This supports the importance of simultaneous interactions of AIPL1-FK506-binding protein with the prenyl moieties of PDE6 and AIPL1-TPR with the Pγ subunit during the folding and/or assembly of PDE6. This study sheds new light on the versatility of TPR domains in protein folding by describing a novel TPR-protein binding partner, Pγ, and revealing that this subunit imparts AIPL1 selectivity for its client.

NMR resonance assignments for the GSPII-B domain of the traffic ATPase PilF from Thermus thermophilus in the apo and the c-di-GMP-bound state.

The PilF protein from the thermophilic bacterium Thermus thermophilus is a traffic ATPase powering the assembly of the DNA translocation machinery as well as of type 4 pili. Thereby PilF mediates the natural transformability of T. thermophilus. PilF contains a C-terminal ATPase domain and three N-terminal domains with partial homology to so-called general secretory pathway II (GSPII) domains. These three GSPII domains (GSPII-A, GSPII-B and GSPII-C) are essential for pilus assembly and twitching motility. They show varying degrees of sequence homology to the N-terminal domain of the ATPase MshE from Vibrio cholerae which binds the bacterial second messenger molecule c-di-GMP. NMR experiments demonstrate that the GSPII-B domain of PilF also binds c-di-GMP with high affinity and forms a 1:1 complex in slow exchange on the NMR time scale. As a prerequisite for structural studies of c-di-GMP binding to the GSPII-B domain of T. thermophilus PilF we present here the NMR resonance assignments for the apo and the c-di-GMP bound state of GSPII-B. In addition, we map the binding site for c-di-GMP on the GSPII-B domain using chemical shift perturbation data and compare the dynamics of the apo and the c-di-GMP-bound state of the GSPII-B domain based on {1H},15N-hetNOE data.

Simple high-resolution NMR spectroscopy as a tool in molecular biology.

NMR is one of the major techniques for investigating the structure, dynamics and interactions between biomolecules. However, non‐experts often experience NMR experimentation and data analysis as intimidating. We discuss a simple yet powerful NMR technique, the so‐called chemical shift perturbation (CSP) analysis, as a tool to elucidate macromolecular interactions in small‐ and medium‐sized complexes, including protein‐protein, protein‐drug, and protein‐DNA/RNA interactions. We discuss current software packages for NMR data analysis and present a new interactive graphical tool implemented in CcpNmr AnalysisAssign version‐3, which can drastically reduce the time required for the CSP analysis. Lastly, we illustrate the usefulness of a protein three‐dimensional structure for interpretation of the CSP data.

Structural Basis for the Interaction between p53 Transactivation Domain and the Mediator Subunit MED25.

Eukaryotic transcription initiation is mediated by interactions between transcriptional activators and the mediator coactivator complex. Molecular interaction of p53 transcription factor with mediator complex subunit 25 (MED25) is essential for its target gene transcription. In this study, we characterized the molecular interaction between p53 transactivation domain (p53TAD) and activator interaction domain (ACID) of MED25 using nuclear magnetic resonance (NMR) spectroscopy. The NMR chemical shift perturbation and isothermal titration calorimetry (ITC) data showed that p53TAD interacted with MED25 ACID mainly through the p53TAD2 sequence motif. Taken together with the mutagenesis data, the refined structural model of MED25 ACID/p53TAD2 peptide complex showed that an amphipathic α-helix of p53TAD2 peptide bound an elongated hydrophobic groove of MED25 ACID. Furthermore, our results revealed the highly conserved mechanism of MED25 interaction with intrinsically unfolded acidic TADs from the transcriptional activators p53, ERM (Ets-related molecule), and herpes simplex virus protein 16 (VP16).

Computational Study of Glycosaminoglycan Specificity for Growth Factor and Chemokine Family Members

Glycosaminoglycans (GAGs), linear polysaccharides with repeating disaccharide units, bind to proteins through primarily electrostatic interactions, which tend to induce considerable non‐specificity of recognition. Yet, GAG–protein interactions are known to regulate various physiological and pathological functions. To date, only one sequence the heparin pentasaccharide sequence that binds to antithrombin has been identified as a specific sequence with therapeutic promise. Are specific GAG sequences so rare despite the millions of natural occurring GAG sequences? Our hypothesis has been that GAG sequences that bind to proteins are not rare but it has been difficult to identify them due to the phenomenal heterogeneity of GAGs and the near impossibility of synthesizing all possible natural (and unnatural) sequences. For example, a natural hexasaccharide sequence belonging to the heparan sulfate family can be of 46,656 types. To overcome this, our lab has developed a computational strategy called as Combinatorial Virtual Library Screening (CVLS), which is exhibit impressive application in identifying sequences displaying a high level of specificity against chosen targets. Here, we extend the applicability of CVLS by adding molecular dynamics (MD) simulations as a powerful approach to identify specific and non‐specific GAG sequences for a particular target. Application of CVLS‐MD approach to well‐known GAG target, fibroblast growth factor 2 (FGF2) and chemokine CXCL13 led to unique understanding on the nature of GAG recognition and origin of specificity for therapeutic targeting. Libraries of 2592 tetrasaccharides (HS04) and 46,656 hexasaccharides (HS06) were screened against both protein targets. CVLS identified 14 HS04 sequences as highly promising sequences for CXCL13, whereas FGF2 was found to be better recognized by 9 HS06 sequences. The co‐complexes of these sequences were studied using MD in the presence of explicit water and analyzed to understand specificity of interaction through analysis of direct and indirect hydrogen bonding, single residue energy decomposition and binding free energy. There was a strong correlation of CVLS‐MD predictions with experimental data. Interesting, FGF2–HS06 co‐complex exhibited differences in hydrogen bonding pattern and binding free energy due to IdoA2S ring puckering (both 1C4 to 2SO), whereas CXCL13 showed preferential recognition of one HS04 binding site of the two possible on protein surface. Most importantly, the CVLS–MD approach identified HS sequences showing specific as well as plastic (non‐specific) hydrogen bonding interactions in solution. The in silico predictions corresponded very well with solution NMR chemical shift perturbation (CSP) data resulting in identification of a specific HS04 sequence that stabilizes the chemokine dimer. Overall, this combined CVLS–MD approach is likely to serve as a promising strategy for the identification of specific and non‐specific GAG sequences against various target proteins.Support or Funding InformationThis work was supported in part by grants from the NIH including HL107152, HL090586 and HL128639. We thank Lortat‐Jacob H, University of Grenoble Alpes, CNRS, CEA, IBS, 38000 Grenoble, France hugues.lortat-jacob@ibs.fr. for experimental dataThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Interplay between membrane curvature and protein conformational equilibrium investigated by solid-state NMR

Many membrane proteins sense and induce membrane curvature for function, but structural information about how proteins modulate their structures to cause membrane curvature is sparse. We review our recent solid-state NMR studies of two virus membrane proteins whose conformational equilibrium is tightly coupled to membrane curvature. The influenza M2 proton channel has a drug-binding site in the transmembrane (TM) pore. Previous chemical shift data indicated that this pore-binding site is lost in an M2 construct that contains the TM domain and a curvature-inducing amphipathic helix. We have now obtained chemical shift perturbation, protein-drug proximity, and drug orientation data that indicate that the pore-binding site is restored when the full cytoplasmic domain is present. This finding indicates that the curvature-inducing amphipathic helix distorts the TM structure to interfere with drug binding, while the cytoplasmic tail attenuates this effect. In the second example, we review our studies of a parainfluenza virus fusion protein that merges the cell membrane and the virus envelope during virus entry. Chemical shifts of two hydrophobic domains of the protein indicate that both domains have membrane-dependent backbone conformations, with the β-strand structure dominating in negative-curvature phosphatidylethanolamine (PE) membranes. 31P NMR spectra and 1H-31P correlation spectra indicate that the β-strand-rich conformation induces saddle-splay curvature to PE membranes and dehydrates them, thus stabilizing the hemifusion state. These results highlight the indispensable role of solid-state NMR to simultaneously determine membrane protein structures and characterize the membrane curvature in which these protein structures exist.

Structural basis for the interaction between DJ-1 and Bcl-XL

DJ-1 is a multifunctional protein associated with Parkinson's disease (PD) and tumorigenesis. In response to ultraviolet B (UVB) irradiation, DJ-1 is translocated into the mitochondria, and its interaction with the mitochondrial protein Bcl-XL protects cells against death. In this study, we characterized the molecular interaction between DJ-1 and Bcl-XL by NMR spectroscopy. The NMR chemical shift perturbation data demonstrated that the oxidized but not the reduced form of DJ-1 binds to the predominantly hydrophobic groove surrounded by the BH1–BH3 domains in Bcl-XL. In addition, our results showed that the C-terminal α8-helix peptide (Cpep) of DJ-1 binds to the pro-apoptotic BH3 peptide-binding hydrophobic groove in Bcl-XL and, thus, acts as a Bcl-XL-binding motif. In combination with the NMR chemical shift perturbation data, a refined structural model of the Bcl-XL/DJ-1 Cpep complex revealed that the binding mode is remarkably similar to that of other Bcl-XL/pro-apoptotic BH3 peptide complexes. Taken together, our results provide a structural basis for the binding mechanism between DJ-1 and Bcl-XL, which will contribute to molecular understanding of the role of mitochondrial DJ-1 in Bcl-XL regulation in response to oxidative stress.

Abstract 5229: High affinity interaction of K-Ras4B HVR with calmodulin

Abstract Ras proteins promote cell proliferation and survival, controlling signal transduction that involves two major pathways, such as Raf/MEK/ERK and PI3K/Akt. K-Ras4B is the most abundant oncogenic isoform. In calcium- and calmodulin (CaM)-rich environments, such as ductal tissues, it plays a critical role in adenocarcinomas promoting PI3K/Akt signaling, particularly in pancreatic, lung, and colorectal cancers. It was suggested that in adenocarcinomas with elevated calcium levels, Ca2+/CaM recruits PI3Kα through interaction with its n/cSH2 domains and sequesters K-Ras4B from the membrane, organizing a CaM/K-Ras4B/PI3Kα ternary complex. Ca2+/CaM can replace the missing receptor tyrosine kinase (RTK) signal, acting to fully activate PI3Kα. Structural data suggests that CaM uniquely binds GTP-bound K-Ras4B but not N-Ras or H-Ras isoforms. Experimental evidence points to the farnesylated hypervariable region (HVR) of K-Ras4B as a major binding domain for CaM. Here, using molecular dynamics (MD) simulations we modeled K-Ras4B HVR interaction with Ca2+/CaM. Initial contacts of K-Ras4B HVR with CaM were determined by the nuclear magnetic resonance (NMR) chemical shift perturbation(CSP) data, which guided major interacting residue pairs between the HVR and CaM. In the simulations, two different topologies of Ca2+/CaM were modeled: CaM with stretched and flexible linkers. CaM has N- and C-lobes connected by a linker, and each lobe has its own hydrophobic pocket. Thus, the hydrophobic farnesyl tail of the HVR can dock into either lobe of CaM. We observed that the HVR strongly interacts with the linker of CaM. The K-Ras4B HVR is highly polybasic with lysine-rich, while the linker region of CaM is negatively charged. The docking of the farnesyl group into the hydrophobic pocket additionally helps to stabilize the HVR/CaM interaction. This added stabilization by the farnesyl is significant in the K-Ras4B/CaM interaction even though the interaction with the Ras catalytic domain is involved. K-Ras4B has only farnesyl modification, while other isoforms bear farnesyl and palmitoyl groups. The additional lipid modification in the HVR would obstruct CaM binding, suggesting CaM's K-Ras4B-specific action. Our structural model of K-Ras4B/CaM association provides plausible clues to the PI3Kα activation involving the ternary complex. The abundant Ca2+/CaM can bind to the p85 domain of PI3Kα while binding to the K-Ras4B farnesylated HVR, releasing catalytic kinase domain autoinhibition and allosterically leading to full PI3Kα activation. Funded by Frederick National Laboratory for Cancer Research, National Institutes of Health, under contract HHSN261200800001E. Citation Format: Hyunbum Jang, Avik Banerjee, Vadim Gaponenko, Ruth Nussinov. High affinity interaction of K-Ras4B HVR with calmodulin [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5229. doi:10.1158/1538-7445.AM2017-5229

Biophysical characterization of Ca2+-binding of S100A5 and Ca2+-induced interaction with RAGE

S100A5 is a calcium-binding protein of S100 family, which represents a major ligand to the receptor for advanced glycation end product (RAGE), a pattern recognition receptor engaged in diverse pathological processes. Here we have characterized calcium binding of S100A5 and the complex formation between S100A5 and RAGE using calorimetry and NMR spectroscopy. S100A5 binds to calcium ions in a sequential manner with the equilibrium dissociation constants (KD) of 1.3 μM and 3.5 μM, which corresponds to the calcium-binding at the C-terminal and N-terminal EF-hands. Upon calcium binding, S100A5 interacts with the V domain of RAGE (RAGE-v) to form a heterotrimer (KD ∼5.9 μM) that is distinct among the S100 family proteins. Chemical shift perturbation data from NMR titration experiments indicates that S100A5 employs the periphery of the dimer interface to interact with RAGE-v. Distinct binding mode and stoichiometry of RAGE against different S100 family proteins could be important to modulate diverse RAGE signaling.

NMR Signal Assignments of Human Adenylate Kinase 1 (hAK1) and its R138A Mutant (hAK1R138A)

Adenylate kinase (AK) enzyme which acts as the catalyst of reversible high energy phosphorylation reaction between ATP and AMP which associate with energetic metabolism and nucleic acid synthesis and signal transmission. This enzyme has three distinct domains: Core, AMP binding domain (AMPbd) and Lid domain (LID). The primary role of AMPbd and LID is associated with conformational changes due to flexibility of two domains. Three dimensional structure of human AK1 has not been confirmed and various mutation experiments have been done to determine the active sites. In this study, AK1R138A which is changed arginine[138] of LID domain with alanine[138] was made and conducted with NMR experiments, backbone dynamics analysis and mo-lecular docking dynamic simulation to find the cause of structural change and substrate binding site. Synthetic human muscle type adenylate kinase 1 (hAK1) and its mutant (AK1R138A) were re-combinded with E. coli and expressed in M9 cell. Expressed proteins were purified and finally gained at 0.520 mM hAK1 and 0.252 mM AK1R138A. Multinuclear multidimensional NMR experiments including HNCA, HN(CO)CA, were conducted for amino acid sequence analysis and signal assignments of HSQC spectrum. Our chemical shift perturbation data is shown LID domain residues and around alanine[138] and per-turbation value(0.22ppm) of valine[179] is consid-ered as inter-communication effect with LID domain and the structural change between hAK1 and AK1R138A.

The C-terminal domains of two homologous Oleaceae β-1,3-glucanases recognise carbohydrates differently: Laminarin binding by NMR

Ole e 9 and Fra e 9 are two allergenic β-1,3-glucanases from olive and ash tree pollens, respectively. Both proteins present a modular structure with a catalytic N-terminal domain and a carbohydrate-binding module (CBM) at the C-terminus. Despite their significant sequence resemblance, they differ in some functional properties, such as their catalytic activity and the carbohydrate-binding ability. Here, we have studied the different capability of the recombinant C-terminal domain of both allergens to bind laminarin by NMR titrations, binding assays and ultracentrifugation. We show that rCtD-Ole e 9 has a higher affinity for laminarin than rCtD-Fra e 9. The complexes have different exchange regimes on the NMR time scale in agreement with the different affinity for laminarin observed in the biochemical experiments. Utilising NMR chemical shift perturbation data, we show that only one side of the protein surface is affected by the interaction and that the binding site is located in the inter-helical region between α1 and α2, which is buttressed by aromatic side chains. The binding surface is larger in rCtD-Ole e 9 which may account for its higher affinity for laminarin relative to rCtD-Fra e 9.

Bile salt recognition by human liver fatty acid binding protein.

Fatty acid binding proteins (FABPs) act as intracellular carriers of lipid molecules, and play a role in global metabolism regulation. Liver FABP (L-FABP) is prominent among FABPs for its wide ligand repertoire, which includes long-chain fatty acids as well as bile acids (BAs). In this work, we performed a detailed molecular- and atomic-level analysis of the interactions established by human L-FABP with nine BAs to understand the binding specificity for this important class of cholesterol-derived metabolites. Protein-ligand complex formation was monitored using heteronuclear NMR, steady-state fluorescence spectroscopy, and mass spectrometry. BAs were found to interact with L-FABP with dissociation constants in the narrow range of 0.6-7 μm; however, the diverse substitution patterns of the sterol nucleus and the presence of side-chain conjugation resulted in complexes endowed with various degrees of conformational heterogeneity. Trihydroxylated BAs formed monomeric complexes in which single ligand molecules occupied similar internal binding sites, based on chemical-shift perturbation data. Analysis of NMR line shapes upon progressive addition of taurocholate indicated that the binding mechanism departed from a simple binary association equilibrium, and instead involved intermediates along the binding path. The co-linear chemical shift behavior observed for L-FABP complexes with cholate derivatives added insight into conformational dynamics in the presence of ligands. The observed spectroscopic features of L-FABP/BA complexes, discussed in relation to ligand chemistry, suggest possible molecular determinants of recognition, with implications regarding intracellular BA transport. Our findings suggest that human L-FABP is a poorly selective, universal BA binder.

NMR Structural Studies of a 52 kDa Heterocylization Domain of the Yersiniabactin Non-Ribosomal Peptide Synthetase

Nonribosomal peptide synthetases (NRPSs) are modular multi-domain enzymatic systems in bacteria and fungi that synthesize a diverse array of secondary metabolites called nonribosomal peptides (NRPs). NRPs encompass broad biological activity from etiological agents in microbial infections to various pharmaceutical applications. Despite their diversity NRPs are synthesized in a similar iterative manner, where each module of the synthetase adds a single substrate to the growing NRP chain. Chain elongation proceeds via peptide bond formation, catalyzed by condensation domains (C), between substrates tethered onto thiolation domains (T) in sequential modules. Condensation domains are sometimes replaced by cyclization domains (Cy) that carry out both condensation and heterocyclization (e.g. cysteines to thiazolines). NRP chain elongation affected by C (or Cy) and cognate T domain interactions is poorly understood due to lack of molecular details. Multidomain X-ray structures revealed only non-functional inter-domain orientations. Solution NMR studies have highlighted the presence of multiple conformers of excised domains in equilibria suggesting that transient domain interactions driven by conformational selection propel NRP chain elongation. Here, we investigate the molecular interactions between a Cy domain and its two cognate T domains from the NRPS Yersiniabactin synthetase using solution NMR techniques. We have determined the NMR solution structure of this excised 52 kDa Cy domain. New NMR methods were developed to overcome challenges in chemical shift assignments and improving the accuracy of distance constraints in the structure determination of this large protein. The interaction interfaces between the Cy and the T domains were mapped by chemical shift perturbation data from titrations of each T domain individually and sequentially into Cy. Our studies lay the foundation for building a model of this ternary complex to better understand domain interactions at a molecular level in NRP synthesis.