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Structure of an LPMO expressed in E.coli (LsAA9A) at 7.00x10^4 Gy
Structural highlights
FunctionLP9A_PANSI Lytic polysaccharide monooxygenase (LPMO) that depolymerizes crystalline and amorphous polysaccharides via the oxidation of scissile alpha- or beta-(1-4)-glycosidic bonds, yielding C1 or C4 oxidation product (PubMed:26928935, PubMed:29057953, PubMed:32818374). Catalysis by LPMOs requires the reduction of the active-site copper from Cu(II) to Cu(I) by a reducing agent and H(2)O(2) or O(2) as a cosubstrate (PubMed:26928935, PubMed:29057953). Is able to cleave phosphoric acid swollen cellulose (PASC) in the presence of a reducing agent, yielding a range of cellooligosaccharides dominated by cellobiose and cellotriose (PubMed:26928935). Activity is less sensitive to the reducing agent potential when cleaving xylan, suggesting that distinct catalytic mechanisms exist for xylan and glucan cleavage (PubMed:29057953).[1] [2] [3] Publication Abstract from PubMedLytic polysaccharide monooxygenases (LPMOs) are copper-dependent enzymes classified into the auxiliary activity (AA) families of the CAZy database. They oxidatively cleave glycosidic bonds in recalcitrant polysaccharides, playing a key role in biomass degradation and contributing to the virulence of some pathogens. The redox state of the active-site copper and its coordination geometry are central to LPMO catalysis, yet the subtle structural consequences of redox and substrate-binding transitions remain insufficiently resolved. In previous work, a comparative X-ray crystallographic analysis of a model AA9 LPMO (LsAA9A) was conducted under four distinct conditions at 100 K: Cu(II), Cu(I) and the corresponding saccharide-bound states, with the Cu(I) state generated by X-ray photoreduction. In this study, LsAA9A crystals were chemically reduced with or without saccharide substrate prior to low-dose X-ray data collection to minimize radiation damage. Copper-coordination distances and angles were determined precisely through triplicate structure determinations (each from an independent crystal) for each condition, revealing small but reproducible geometry differences across key states in the LPMO catalytic pathway. In order to identify the most significant differences, statistical evaluation using one-way analysis of variance (ANOVA), followed by Tukey-Kramer post hoc tests and pairwise t-tests, was carried out. Within the assumptions made, statistically significant differences in the coordinated Cu-His1 N(delta1) and Cu-Tyr O(eta) distances, and in the coordination angles theta(2), theta(3) and theta(T), are observed across the four states and are discussed in terms of the mechanism and in relation to our previous study. To complement cryogenic data, multi-crystal data sets at increasing X-ray dose were collected at room temperature to track photoreduction of the copper site, with the specific aim of detecting the transition of Cu(II) to fully reduced Cu(I). This could not finally be achieved due to the onset of global radiation damage; however, a subset of the reduction-linked geometric changes were detectable, indicating that a partial transition may have occurred. Experimental estimation of copper-site geometry reproducibility in biologically relevant redox and saccharide-bound states of a model lytic polysaccharide monooxygenase.,Huang Z, Wei Q, Nan J, Norholm MHH, Liu Z, Hernandez-Rollan C, Johansen KS, Lo Leggio L Acta Crystallogr D Struct Biol. 2026 Aug 1;82(Pt 8):886-899. doi: , 10.1107/S2059798326005966. Epub 2026 Jul 17. PMID:42466526[4] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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