Characterization of two family AA9 LPMOs from Aspergillus tamarii with distinct activities on xyloglucan reveals structural differences linked to cleavage specificity.

Antonielle V Monclaro,Edivaldo X F Filho,Marcos M C Costa,Glaucia E O Midorikawa,Vincent G H Eijsink,Anikó Várnai,Gabriel S C Alves,Robert N G Miller,Dejan M Petrović,Jean-Guy Berrin

doi:10.1371/journal.pone.0235642

Abstract

Aspergillus tamarii grows abundantly in naturally composting waste fibers of the textile industry and has a great potential in biomass decomposition. Amongst the key (hemi)cellulose-active enzymes in the secretomes of biomass-degrading fungi are the lytic polysaccharide monooxygenases (LPMOs). By catalyzing oxidative cleavage of glycoside bonds, LPMOs promote the activity of other lignocellulose-degrading enzymes. Here, we analyzed the catalytic potential of two of the seven AA9-type LPMOs that were detected in recently published transcriptome data for A. tamarii, namely AtAA9A and AtAA9B. Analysis of products generated from cellulose revealed that AtAA9A is a C4-oxidizing enzyme, whereas AtAA9B yielded a mixture of C1- and C4-oxidized products. AtAA9A was also active on cellopentaose and cellohexaose. Both enzymes also cleaved the β-(1→4)-glucan backbone of tamarind xyloglucan, but with different cleavage patterns. AtAA9A cleaved the xyloglucan backbone only next to unsubstituted glucosyl units, whereas AtAA9B yielded product profiles indicating that it can cleave the xyloglucan backbone irrespective of substitutions. Building on these new results and on the expanding catalog of xyloglucan- and oligosaccharide-active AA9 LPMOs, we discuss possible structural properties that could underlie the observed functional differences. The results corroborate evidence that filamentous fungi have evolved AA9 LPMOs with distinct substrate specificities and regioselectivities, which likely have complementary functions during biomass degradation.

Highlights

The genome of A. tamarii CBS 117626 has only recently been published, and it contains nine predicted proteins annotated as AA9 lytic polysaccharide monooxygenases (LPMOs) [54]
Comparison of the C-terminus of AtAA9C with the C-termini of proteins sharing >90% identity, which were all LPMOs from Aspergillus species, indicated that, in the AtAA9C sequence derived from the RNA-seq data, this domain lacks ca. 50 amino acids (S1B Fig in S1 Appendix)
Transcriptome analysis of A. tamarii growing on sugarcane bagasse as a carbon source revealed expression of seven AA9 LPMOs [39]

Summary

Introduction

243663) for DMP, VGHE and AV and Bio4Fuels All funders provided support in the form of salaries for authors but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of the authors are articulated in the ‘Author contributions’ section

Methods

Results

Conclusion