RESUMO
The cold-adapted xylanases can catalyze at low temperature and hold great potential in food industry applications. Here we describe the first crystal structure of a cold-adapted glycoside hydrolase (GH) family 10 xylanase XynGR40 and its complex with xylobiose at 2.15 and 2.50Å resolution. The enzyme folds into a typical GH10 (ß/α)8 TIM-barrel, with E132 and E243 serving as the catalytic residues. The xylobiose was observed to occupy the -1 and -2 subsites. Structural comparison with a thermophilic GH10 xylanase highlighting various parameters that may explain the cold adaptation features were analyzed. Synergistic effects of the increased exposure of hydrophobic residues, the higher flexibility of substrate-binding residues, more flexible loops, and the ratios of special amino acid residues, may result in the cold adaptation of XynGR40.
Assuntos
Adaptação Fisiológica , Dissacarídeos/química , Endo-1,4-beta-Xilanases/química , Conformação Proteica , Sítios de Ligação , Catálise , Temperatura Baixa , Cristalografia por Raios X , Dissacarídeos/metabolismo , Endo-1,4-beta-Xilanases/genética , Endo-1,4-beta-Xilanases/metabolismo , Microbioma Gastrointestinal , Interações Hidrofóbicas e Hidrofílicas , Especificidade por SubstratoRESUMO
Structures of the iridoid synthase nepetalactol synthase in the presence of NAD(+) , NADPH or NAD(+) /10-oxogeranial were solved. The 10-oxogeranial substrate binds in a transoid-O1-C3 conformation and can be reduced by hydride addition to form the byproduct S-10-oxo-citronellal. Tyr178 Oζ is positioned 2.5â Å from the substrate O1 and provides the second proton required for reaction. Nepetalactol product formation requires rotation about C1-C2 to form the cisoid isomer, leading to formation of the cis-enolate, together with rotation about C4-C5, which enables cyclization and lactol production. The structure is similar to that of progesterone-5ß-reductase, with almost identical positioning of NADP, Lys146(147), Tyr178(179), and F342(343), but only Tyr178 and Phe342 appear to be essential for activity. The transoid 10-oxogeranial structure also serves as a model for ß-face hydride attack in progesterone 5ß-reductases and is of general interest in the context of asymmetric synthesis.