Structural and electronic modulations of lytic polysaccharide monooxygenase (LPMO) upon chitin binding: insights from X-ray spectroscopy

Abstract

Lytic polysaccharide monooxygenases (LPMOs) play a critical role in the depolymerization of recalcitrant polysaccharides, such as chitin, making them of interest in biotechnological applications. These interfacial enzymes are also of great chemical interest because of their unique monocopper catalytic center and their ability to activate high energy C–H bonds. This report investigates the structural and electronic changes at the copper (Cu) site of an LPMO, SmAA10A, upon binding of its chitin substrate, utilizing a suite of spectroscopic and computational methods. Herein, we present the first reported X-ray Absorption (XAS) and Emission (XES) spectroscopic data on substrate-bound LPMO. By comparing the Cu(II) and Cu(I) states of SmAA10A in both the chitin-bound and unbound states, we provide insights into the structural adjustments facilitating substrate specificity and productive catalytic turnover. Our results indicate a substrate binding-induced conformational change in Cu(I) site geometry and concurrent modulations to the electronic structure, which prime the enzyme for targeted C–H activation with an H₂O₂ co-substrate. This work offers an atomistic understanding of interaction dynamics between the LPMO Cu site and the chitin substrate, advancing our knowledge of LPMO functionality and substrate specificity.