PDBsum entry 6rs6

Unknown function

PDB id: 6rs6

Contents

Protein chain

221 a.a.

Ligands

NAG-NAG-BMA

MAN

PEG

GLY ×2

SER

Metals

_CL ×2

Waters ×215

References listed in PDB file

Key reference

• Title: Insights into an unusual auxiliary activity 9 family member lacking the histidine brace motif of lytic polysaccharide monooxygenases.
• Authors: K.E.H.Frandsen, M.Tovborg, C.I.Jørgensen, N.Spodsberg, M.N.Rosso, G.R.Hemsworth, E.F.Garman, G.W.Grime, J.N.Poulsen, T.S.Batth, S.Miyauchi, A.Lipzen, C.Daum, I.V.Grigoriev, K.S.Johansen, B.Henrissat, J.G.Berrin, L.Lo leggio.
• Ref.: J Biol Chem, 2019, 294, 17117-17130. [DOI no: 10.1074/jbc.RA119.009223]
• PubMed id: 31471321

Abstract

Lytic polysaccharide monooxygenases (LPMOs) are redox-enzymes involved in biomass degradation. All characterized LPMOs possess an active site of two highly conserved histidine residues coordinating a copper ion (the histidine brace), which are essential for LPMO activity. However, some protein sequences that belong to the AA9 LPMO family display a natural N-terminal His to Arg substitution (Arg-AA9). These are found almost entirely in the phylogenetic fungal class Agaricomycetes, associated with wood decay, but no function has been demonstrated for any Arg-AA9. Through bioinformatics, transcriptomic, and proteomic analyses we present data, which suggest that Arg-AA9 proteins could have a hitherto unidentified role in fungal degradation of lignocellulosic biomass in conjunction with other secreted fungal enzymes. We present the first structure of an Arg-AA9, LsAA9B, a naturally occurring protein from Lentinus similis The LsAA9B structure reveals gross changes in the region equivalent to the canonical LPMO copper-binding site, whereas features implicated in carbohydrate binding in AA9 LPMOs have been maintained. We obtained a structure of LsAA9B with xylotetraose bound on the surface of the protein although with a considerably different binding mode compared with other AA9 complex structures. In addition, we have found indications of protein phosphorylation near the N-terminal Arg and the carbohydrate-binding site, for which the potential function is currently unknown. Our results are strong evidence that Arg-AA9s function markedly different from canonical AA9 LPMO, but nonetheless, may play a role in fungal conversion of lignocellulosic biomass.