Cel7A

Cel7A is the gene encoding cellobiohydrolase I (CBH I), a processive exocellulase in the glycoside hydrolase family 7 (GH7). It is a major cellulase produced by filamentous fungi such as Trichoderma reesei (Hypocrea jecorina) and is a key component of industrial enzyme cocktails used for lignocellulosic biomass saccharification. Cel7A acts on cellulose, cleaving cellobiose units from the reducing ends of cellulose chains and thereby contributing to the breakdown of crystalline and amorphous cellulose.

Structure and domains: The Cel7A protein is secreted and typically exhibits a modular architecture that includes an N-terminal signal peptide, a catalytic GH7 domain, a flexible Ser/Thr-rich linker, and a C-terminal cellulose-binding module (CBM1). The CBM1 enhances binding to insoluble cellulose and increases overall catalytic efficiency on crystalline substrates. Variants lacking the CBM or with altered linkers are studied to understand the contributions of non-catalytic regions to activity and stability.

Mechanism and specificity: Cel7A operates through a processive mechanism, moving along the cellulose chain while hydrolyzing β-1,4-glycosidic bonds to release cellobiose. The catalytic center contains conserved residues, including an aspartate and a glutamate, which participate in acid–base catalysis within a tunnel-like active site that accommodates single cellulose chains.

Regulation and application: Expression of cel7a is induced by cellulose and related substrates, and secretion occurs in standard fungal production systems. The enzyme is susceptible to product inhibition by cellobiose and, to a lesser extent, glucose. In industry, Cel7A is used in combination with other cellulases to optimize lignocellulose hydrolysis, contributing significantly to cellulose deconstruction in biofuel and bioprocessing workflows.