Molecular dynamics study of in silico mutations in the auto-inhibitory loop of human endothelial nitric oxide synthase FMN sub-domain

Structural flexibility of the peptide linker connecting two domains is essential for the functioning of multi-domain complex. Nitric oxide synthase (NOS) isoforms contain the oxygenase and the reductase domains connected by calmodulin binding linker (CBL) region. Additionally, the endothelial NOS (eNOS) isoform contain an auto-inhibitory loop (AI) in the FMN reductase sub-domain which represses the inter-domain electron transfer process. Binding of Ca²⁺-Calmodulin complex on the CBL region relieves the AI loop repression and facilitates electron transfer from FMN in the reductase domain to the heme in the oxygenase domain. Few experimental studies have reported that in vitro mutation of Serine-615 (S615D) and Serine-633 (S633D) in the FMN reductase sub-domain to aspartic acid increased NO production and increased Ca²⁺ sensitivity. To understand the role of AI loop in eNOS repression and activation in serine mutants (S615D and S633D), we modelled the FMN reductase sub-domain of human eNOS protein with and without the CBL region. Molecular dynamics simulations performed indicated that the mutant protein AI loop structure was stabilized by salt bridge formed between D615 and R602. It was also found that mutation increased the flexibility of C-terminal residues of eNOS CBL region. The hinge-like movement of the AI loop allowed rotation of the FMN sub-domain clockwise which may favour electron-transfer in the mutant protein. This study provides insight on mutation (S615D and S633D) induced changes in AI loop and increased flexibility of CBL region which may lead to the protein activation and may also facilitate Calmodulin binding at physiological Ca²⁺ concentration. Graphical Abstract Mutation of amino acid residues contribute to structural changes at molecular level leading to alteration in protein dynamics and its function. Serine-615 and Serine-633 in the auto-inhibitory loop of human eNOS reductase model was mutated to aspartic acid in silico and molecular dynamics simulations of the protein showed that steric hindrance due to mutation altered the auto-inhibitory loop rearrangement and the FMN sub-domain movement favouring electron transfer.

Bioinformatics Analysis of Upstream Region and Protein Structure of Fungal Phytase Gene

Phytase increases the bioavailability of phytate phosphorus in seed-based animal feeds and reduces the phosphorus pollution of animal waste. Since most animal feeds for pellets are heated up to 65-80 °C, the production of a thermostable structure for phytase can be useful. In this study, we sought to perform bioinformatics analysis of the upstream region and protein structure of fungal phytase to improve its expression and thermostability properties. We used bioinformatics methods such as similarity search, multiple alignment, statistical analysis of physicochemical properties of amino acids, pattern recognition, and protein modeling to find out the effective factors in heat resistance of phytase. Change in Gibbs free energy (ΔG) of the best pattern promoter resulting from the interaction between RNA polymerase and the promoter sequences of modified genes of phytase was equal to -9 kcalmol-1, which is lower compared to other interactions. The evaluation of the three-dimensional structure of new phytases showed that amino acid substitutions aimed at improving thermostability did not change the form and structure of the protein. The results of Prochek, Whatcheck, and ERRAT for structural analysis and verification were 84, 72, and 70, respectively, that were satisfactory.

The Dark Proteome Database

Background

Recently we surveyed the dark-proteome, i.e., regions of proteins never observed by experimental structure determination and inaccessible to homology modelling. Surprisingly, we found that most of the dark proteome could not be accounted for by conventional explanations (e.g., intrinsic disorder, transmembrane domains, and compositional bias), and that nearly half of the dark proteome comprised dark proteins, in which the entire sequence lacked similarity to any known structure. In this paper we will present the Dark Proteome Database (DPD) and associated web services that provide access to updated information about the dark proteome.

Results

We assembled DPD from several external web resources (primarily Aquaria and Swiss-Prot) and stored it in a relational database currently containing ~10 million entries and occupying ~2 GBytes of disk space. This database comprises two key tables: one giving information on the ‘darkness’ of each protein, and a second table that breaks each protein into dark and non-dark regions. In addition, a second version of the database is created using also information from the Protein Model Portal (PMP) to determine darkness. To provide access to DPD, a web server has been implemented giving access to all underlying data, as well as providing access to functional analyses derived from these data.

Conclusions

Availability of this database and its web service will help focus future structural and computational biology efforts to study the dark proteome, thus providing a basis for understanding a wide variety of biological functions that currently remain unknown.

Availability and implementation

DPD is available at http://darkproteome.ws . The complete database is also available upon request. Data use is permitted via the Creative Commons Attribution-NonCommercial International license (http://creativecommons.org/licenses/by-nc/4.0/ ).

Electronic supplementary material

The online version of this article (doi:10.1186/s13040-017-0144-6) contains supplementary material, which is available to authorized users.

How to Choose the Suitable Template for Homology Modelling of GPCRs: 5-HT7 Receptor as a Test Case

G protein-coupled receptors (GPCRs) are a super-family of membrane proteins that attract great pharmaceutical interest due to their involvement in almost every physiological activity, including extracellular stimuli, neurotransmission, and hormone regulation. Currently, structural information on many GPCRs is mainly obtained by the techniques of computer modelling in general and by homology modelling in particular. Based on a quantitative analysis of eighteen antagonist-bound, resolved structures of rhodopsin family "A" receptors - also used as templates to build 153 homology models - it was concluded that a higher sequence identity between two receptors does not guarantee a lower RMSD between their structures, especially when their pair-wise sequence identity (within trans-membrane domain and/or in binding pocket) lies between 25 % and 40 %. This study suggests that we should consider all template receptors having a sequence identity ≤50 % with the query receptor. In fact, most of the GPCRs, compared to the currently available resolved structures of GPCRs, fall within this range and lack a correlation between structure and sequence. When testing suitability for structure-based drug design, it was found that choosing as a template the most similar resolved protein, based on sequence resemblance only, led to unsound results in many cases. Molecular docking analyses were carried out, and enrichment factors as well as attrition rates were utilized as criteria for assessing suitability for structure-based drug design.

Homology Modeling, Validation and Dynamics of the G Protein-coupled Estrogen Receptor 1 (GPER-1)

Estrogens exert their action mainly by binding three receptors, namely estrogen receptors α and β (ERα and ERβ) and GPER-1 (G-protein coupled estrogen receptor 1). While the patho-physiological role of both ERα and ERβ has been deeply investigated, the role of GPER-1 in estrogens' signaling has not been clearly defined yet. Unfortunately, only few GPER-1 selective ligands were discovered so far, and the real efficiency of such compounds is still matter of debate. To better understand the physiological relevance of GPER-1, new selective chemical probes are higly needed. In this scenario, we report herein the generation and validation of a three-dimensional (3-D) GPER-1 homology model by means of docking studies and molecular dynamics simulations. The model thus generated was employed to (i) decipher the structural basis underlying the ability of estrogens and some Selective Estrogen Receptor Modulators (SERMs) to bind GPER-1 and classical ERα and ERβ, and (ii) generate a reliable G1/GPER-1 complex useful in rationalizing the pharmacological profile of G1 reported in the literature. The G1/GPER-1 complex herein reported could be further exploited in drug design approaches aimed at improving the pharmacological profile of G1 or at identifying new chemical entities (NCEs) as potential modulators of GPER-1.

Homology modelling and molecular docking studies of human placental cadherin protein for its role in teratogenic effects of anti-epileptic drugs

Anti-epileptic drugs (AEDs) have high risk of teratogenic side effects, including neural tube defects while mother is on AEDs for her own prevention of convulsions during pregnancy. The present study investigated the interaction of major marketed AEDs and human placental (hp)-cadherin protein, in-silico, to establish the role of hp-cadherin protein in teratogenicity and also to evaluate the importance of Ca(2+) ion in functioning of the protein. A set of 21 major marketed AEDs were selected for the study and 3D-structure of hp-cadherin was constructed using homology modelling and energy minimized using MD simulations. Molecular docking studies were carried out using selected AEDs as ligand with hp-cadherin (free and bound Ca(2+) ion) to study the behavioural changes in hp-cadherin due to presence of Ca(2+) ion. The study reflected that four AEDs (Gabapentin, Pregabalin, Remacimide and Vigabatrine) had very high affinity towards hp-cadherin and thus the later may have prominent role in the teratogenic effects of these AEDs. From docking simulation analysis it was observed that Ca(2+) ion is required to make hp-cadherin energetically favourable and sterically functional.

Molecular Dynamics Simulation of Rap1 Myb-type domain in Saccharomyces cerevisiae

Telomere is a nucleoprotein complex that plays important role in stability and their maintenance and consists of random repeats of species specific motifs. In budding Saccharomyces cerevisiae, Repressor Activator Protein 1 (Rap1) is a sequence specific protein that involved in transcriptional regulation. Rap1 consist of three active domains like N-terminal BRCT-domain, DNA-binding domain and C-terminal RCT-domain. In this study the unknown 3D structure of Myb-type domain (having 61 residues) within DNAbinding domain was modeled by Modeller7, and verified using different online bioinformatics tools (ProCheck, WhatIf, Verify3D). Dynamics of Myb-type domain of Rap1was carried out through simulation studies using GROMACS software. Time dependent interactions among the molecules were analyzed by Root Mean Square Deviation (RMSD), Radius of Gyration (Rg) and Root Mean Square Fluctuation (RMSF) plots. Motional properties in reduced dimension were also performed by Principal Component Analysis (PCA). Result indicated that Rap1 interacts with DNA major groove through its Helix Turn Helix motifs. Helix 3 was rigid, less amount of fluctuation was found as it interacts with DNA major groove. Helix2 and N-terminal having considerable fluctuation in the time scale.