EglC, a new endoglucanase from Aspergillus niger with major activity towards xyloglucan

A novel gene, eglC, encoding an endoglucanase, was cloned from Aspergillus niger. Transcription of eglC is regulated by XInR, a transcriptional activator that controls the degradation of polysaccharides in plant cell walls. EgIC is an 858-amino-acid protein and contains a conserved C-terminal cellulose-binding domain. EgIC can be classified in glycoside hydrolase family 74. No homology to any of the endoglucanases from Trichoderma reesei was found. In the plant cell wall xyloglucan is closely linked to cellulose fibrils. We hypothesize that the EgIC cellulose-binding domain anchors the enzyme to the cellulose chains while it is cleaving the xyloglucan backbone. By this action it may contribute to the degradation of the plant cell wall structure together with other enzymes, including hemicellulases and cellulases. EgIC is most active towards xyloglucan and therefore is functionally different from the other two endoglucanases from A. niger, EgIA and EgIB, which exhibit the greatest activity towards beta-glucan. Although the mode of action of EgIC is not known, this enzyme represents a new enzyme function involved in plant cell wall polysaccharide degradation by A. niger.