Molecular dynamics-based structural insights of the first putative endoglucanase, PsGH5A of glycoside hydrolase family 5 from Pseudopedobacter saltans.

Abstract

The putative endoglucanase, PsGH5A, from Pseudopedobacter saltans of family GH5 contains a catalytic module, PsGH5 (β/α)8-TIM barrel), at N-terminal followed by a family 6 carbohydrate-binding module (CBM6, β-sandwich). Superposition of PsGH5A with PDB homologs revealed Glu220 and Glu318 as evolutionarily conserved and catalytic residues performing the hydrolysis through retaining-type mechanism, a canonical property of GH5 family. PsGH5A showed higher affinity for longer cellooligosaccharides, as long as cellodecaose with binding free energy (∆G) of - 13.72kcal/mol upon the molecular docking, thereby indicating the endo-mode of hydrolysis. The radius of gyration, Rg (2.7nm), and solvent accessible surface area, SASA (229.6 nm2), of PsGH5A-Cellotetraose complex were determined by MD simulation which was lower than that of PsGH5A (Rg, 2.8nm, SASA, 267 nm2) demonstrating the compactness and affinity of PsGH5A with the cellulosic ligands. Cellulose compatibility of PsGH5A was further confirmed by MMPBSA and per-residue decomposition analysis, where notable ∆G of - 54.38kcal/mol for PsGH5A-Cellotetraose complex was observed. Thus, PsGH5A could be potentially an efficient endoglucanase as it accommodated larger cellooligosaccharides at its active-site. PsGH5A is the first putative endoglucanase studied here from P. saltans which could be genome-mined for lignocellulosic biomass saccharification in the renewable energy sector. The 3-D structure of PsGH5A generated by AlphaFold2, RaptorX, SwissModel, Phyre2 and Robetta tool; YASARA was used for energy minimization of built models. UCLA SAVES-v6 was used for quality assessment of models. Molecular Docking was performed using SWISS-DOCK server and Chimera software. Molecular Dynamics simulations and MMPBSA analysis of PsGH5A and PsGH5A-Cellotetraose complex were performed on GROMACS 2019.6.