Banca de DEFESA: SERGIO RUSCHI BERGAMACHI SILVA
Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.DISCENTE : SERGIO RUSCHI BERGAMACHI SILVA
DATA : 31/08/2018
HORA: 14:00
LOCAL: Auditório do CCET
TÍTULO:
ANALYSIS AND IMPROVEMENT OF STRUCTURAL, ENERGETIC AND DYNAMIC PROPERTIES OF A GH11 XYLANASE VIA MOLECULAR DYNAMICS
PALAVRAS-CHAVES:
xylanase; molecular dynamics; mutants; multidomain enzymes; biotechnological development
PÁGINAS: 159
GRANDE ÁREA: Ciências Exatas e da Terra
ÁREA: Química
SUBÁREA: Físico-Química
ESPECIALIDADE: Química Teórica
RESUMO:
The lignocellulosic ethanol production by enzymatic route has gained space among the industrial processes in order to replace the traditional acid treatment. Xylanases (E.C. 3.2.1.8) constitute a class of enzymes present in the enzymatic cocktail used for this purpose and have great industrial / commercial interest due to their high versatility in several known processes. In this context, some properties of biotechnological interest of a GH11 family xylanase were evaluated via molecular dynamics (MD) simulations. In a first study, we performed MD simulations of a xylanase produced by Bacillus subtilis (XynA) and a quadruple mutant (Gln7His, Gly13Arg, Ser22Pro and Ser179Cys) which display an higher optimum catalytic temperature (20ºC) in relation to native. MD results suggest possible strategies for engineering GH11 xylanases to produce thermostable enzymes. Mutations in regions that exhibit reduced flexibility should preserve rigidity, but their substitution may be chosen to favorably affect other properties, such as solvation or hydrophobic interactions. The data do not only explain the thermostability effect of a GH11 xylanase observed in previous experiments of direct evolution, but also provides information for the planning of other thermostable GH11 mutants by rational design. In a second study, the target was a chimera formed between a xylanolytic domain (XynA) and a xylose binding protein (XBP) which had an experimental catalytic efficiency almost 3.5 times higher than the same non-chimerized xylanase. The factors responsible for this discrepancy were understood by MD simulations. The results suggested the formation and stabilization of a protein-protein interface between the two domains in the presence and absence of xylose in the active site of XBP. Interaction Potential Energy values (IPE) as a function of time show a greater stabilization in the interactions of this interface for xylose bound structure compared to the xylose free one. Structural parameters such as flexibility and volume of the active site were also evaluated. In general, the results suggest that the chimera has a more rigid structure in relation to free xylanase, and in particular the thumb region, which controls active site exposure, demonstrates a significant reduction in flexibility. Finally, MD simulations at different pHs were performed in order to understand the drastic drop (> 50%) in the catalytic activity of this chimera in acidic environments, and, thus, to aggregate information to increase its resistance in such conditions. Solvent accessible surface (SAS) data indicate that acid environments decrease about ten times the SAS of one of the catalytic glutamates required to occur in the substrate breaking reaction. Therefore, there is no possibility of xylan approximation due to this shielding, reflecting in the experimental data of catalytic activity. The thesis reinforces the descriptive and predictive capacities of the MD simulations in the biotechnological development of GH11 xylanases.
MEMBROS DA BANCA:
Presidente - 1959889 - DAVI SERRADELLA VIEIRA
Interno - 1859346 - MIGUEL ANGELO FONSECA DE SOUZA
Externo ao Programa - 1893445 - EUZEBIO GUIMARAES BARBOSA
Externo à Instituição - GUSTAVO DE MIRANDA SEABRA - UFPE
Externo à Instituição - GUTTO RAFFYSON SILVA DE FREITAS - IFRN