RESUMO
A thermostable variant of the mesophilic xylanase A from Bacillus subtilis (BsXynA-G3_4x) contains the four mutations Gln7His, Gly13Arg, Ser22Pro, and Ser179Cys. The crystal structure of the BsXynA-G3_4x has been solved, and the local environments around each of these positions investigated by molecular dynamics (MD) simulations at 328K and 348K. The structural and MD simulation results were correlated with thermodynamic data of the wild-type enzyme, the 4 single mutants and the BsXynA-G3_4x. This analysis suggests that the overall stabilizing effect is entropic, and is consistent with solvation of charged residues and reduction of main-chain flexibility. Furthermore, increased protein-protein hydrogen bonding and hydrophobic interactions also contribute to stabilize the BsXynA-G3_4x. The study revealed that a combination of several factors is responsible for increased thermostability of the BsXynA-G3_4x; (i) introduction of backbone rigidity in regions of high flexibility, (ii) solvation effects and (iii) hydrophobic contacts.