Structure of the catalytic core module of the Chaetomium thermophilum family GH6 cellobiohydrolase Cel6A

TY - JOUR

T1 - Structure of the catalytic core module of the Chaetomium thermophilum family GH6 cellobiohydrolase Cel6A

AU - Thompson, Andrew J.

AU - Heu, Tia

AU - Shaghasi, Tarana

AU - Benyamino, Romil

AU - Jones, Aubrey

AU - Friis, Esben P.

AU - Wilson, Keith S.

AU - Davies, Gideon J.

PY - 2012/8

Y1 - 2012/8

N2 - Cellulases, including cellobiohydrolases and endoglucanases, are important enzymes involved in the breakdown of the polysaccharide cellulose. These catalysts have found widescale industrial applications, particularly in the paper and textile industries, and are now finding use in 'second-generation' conversion of biomass to biofuels. Despite this considerable biotechnological application, and undoubted future potential, uncertainty remains as to the exact reaction mechanism of the inverting cellulases found in the GH6 family of carbohydrate-active enzymes. In order to gain additional understanding as to how these societally beneficial biocatalysts function, the crystal structure of a GH6 cellobiohydrolase from Chaetomium thermophilum, CtCel6A, has been solved. This structure reveals a distorted alpha/beta-barrel fold comprising a buried tunnel-like active site quite typical of Cel6A enzymes. Analysis of an enzyme-product complex (cellobiose in the -3 and -2 subsites and cellotetraose in subsites +1 to +4) supports the hypothesis that this group of enzymes act via an atypical single-displacement mechanism. Of particular note in this analysis is an active-centre metal ion, Li+, the position of which matches the position of the positively charged anomeric carbon of the oxocarbenium-ion-like transition state.

AB - Cellulases, including cellobiohydrolases and endoglucanases, are important enzymes involved in the breakdown of the polysaccharide cellulose. These catalysts have found widescale industrial applications, particularly in the paper and textile industries, and are now finding use in 'second-generation' conversion of biomass to biofuels. Despite this considerable biotechnological application, and undoubted future potential, uncertainty remains as to the exact reaction mechanism of the inverting cellulases found in the GH6 family of carbohydrate-active enzymes. In order to gain additional understanding as to how these societally beneficial biocatalysts function, the crystal structure of a GH6 cellobiohydrolase from Chaetomium thermophilum, CtCel6A, has been solved. This structure reveals a distorted alpha/beta-barrel fold comprising a buried tunnel-like active site quite typical of Cel6A enzymes. Analysis of an enzyme-product complex (cellobiose in the -3 and -2 subsites and cellotetraose in subsites +1 to +4) supports the hypothesis that this group of enzymes act via an atypical single-displacement mechanism. Of particular note in this analysis is an active-centre metal ion, Li+, the position of which matches the position of the positively charged anomeric carbon of the oxocarbenium-ion-like transition state.

KW - CRYSTALLINE CELLULOSE

KW - CARBOHYDRATE-BINDING MODULES

KW - MOLECULAR-GRAPHICS

KW - HUMICOLA-INSOLENS

KW - TRICHODERMA-REESEI

KW - THERMOSTABLE ENZYMES

KW - HYDROLYSIS

KW - TRANSITION-STATE ANALOGS

KW - CELLULASES

KW - ACTIVE-SITE

UR - http://www.scopus.com/inward/record.url?scp=84864867397&partnerID=8YFLogxK

U2 - 10.1107/S0907444912016496

DO - 10.1107/S0907444912016496

M3 - Article

SN - 0907-4449

VL - 68

SP - 875

EP - 882

JO - Acta Crystallographica. Section D, Biological Crystallography

JF - Acta Crystallographica. Section D, Biological Crystallography

IS - 8

ER -