Chitin-binding mechanism of a CBM73 module derived from a lytic polysaccharide monooxygenase from Vibrio campbellii

A lytic polysaccharide monooxygenase from Vibrio campbellii (VhLPMO10A) consists of four functional domains including an N-terminal AA10 catalytic domain (CatD) and a C-terminal CBM73 carbohydrate-binding domain. Phylogenetic analysis of CBM73s from AA10 LPMO and GH18/GH19 chitinases revealed that CBM73 from VhLPMO10A (VhCBM73) belongs a clade different from that of a well-studied CBM73 from Cellvibrio japonicus AA10 LPMO (CjCBM73, Madland et al., J. Biol. Chem. 297 (2021) 101084). A recombinant VhCBM73 protein did not bind chitooligosaccharides, but it almost equally bound colloidal chitins prepared from squid pen/crab shell. Mutations of Tyr437, Trp441, and Trp456 of VhCBM73 to alanine (Y437A, W441A, and W456A) revealed that the effects were most intensive in Y437A, moderate in W441A, but insignificant in W456A. We concluded that a single chitin chain more hydrated interact with the binding path spanning from Tyr437 to Trp441 of VhCBM73, while multiple chitin chains (chitin surface) interact with a wider binding surface of CjCBM73. VhCBM73 and CjCBM73 may have differently evolved to acquire different binding strategies for enhancing the LPMO function.