Structure of Ps_Cel5A and its structural adaptation for transglycosylation
What is it about?
Some bacterial GH5_5 endoglucanases are endowed with transglycosylation activity while the fungal counterparts are not. Structural adaptations must exist to explain such a difference. We've characterized Ps_Cel5A, a GH5_5 of Pseudomonas stutzeri, and demonstrated its hydrolytic and transglycosylating activities. In addition, we've determined its structure, enabling the comparison with the structures of fungal GH5_5 enzymes. While the negative subsites are well conserved, the positive subsites displayed two major adaptations. Firstly, two positively charged residues, an arginine and a lysine, are present in the positive subsites of Ps_Cel5A. Secondly, a disulfide bridge is absent in Ps_Cel5A, increasing flexibility of the positive subsites.
Why is it important?
Our results show the adaptation of the positive subsites of Ps_Cel5A linked to transglycosylation. They corroborate also our previous study on RBcel1, another bacterial GH5_5 endoglucanase/transglycosylase. Both enzymes have an arginine residue in the +1/+2 subsites. This arginine residue is, however, not conserved indicating a convergent evolution.