Biochemical and structural features of diverse bacterial glucuronoyl esterases facilitating recalcitrant biomass conversion
Artikel i vetenskaplig tidskrift, 2018

Background
Lignocellulose is highly recalcitrant to enzymatic deconstruction, where the recalcitrance primarily results from chemical linkages between lignin and carbohydrates. Glucuronoyl esterases (GEs) from carbohydrate esterase family 15 (CE15) have been suggested to play key roles in reducing lignocellulose recalcitrance by cleaving covalent ester bonds found between lignin and glucuronoxylan. However, only a limited number of GEs have been biochemically characterized and structurally determined to date, limiting our understanding of these enzymes and their potential exploration.
Results
Ten CE15 enzymes from three bacterial species, sharing as little as 20% sequence identity, were characterized on a range of model substrates; two protein structures were solved, and insights into their regulation and biological roles were gained through gene expression analysis and enzymatic assays on complex biomass. Several enzymes with higher catalytic efficiencies on a wider range of model substrates than previously characterized fungal GEs were identified. Similarities and differences regarding substrate specificity between the investigated GEs were observed and putatively linked to their positioning in the CE15 phylogenetic tree. The bacterial GEs were able to utilize substrates lacking 4-OH methyl substitutions, known to be important for fungal enzymes. In addition, certain bacterial GEs were able to efficiently cleave esters of galacturonate, a functionality not previously described within the family. The two solved structures revealed similar overall folds to known structures, but also indicated active site regions allowing for more promiscuous substrate specificities. The gene expression analysis demonstrated that bacterial GE-encoding genes were differentially expressed as response to different carbon sources. Further, improved enzymatic saccharification of milled corn cob by a commercial lignocellulolytic enzyme cocktail when supplemented with GEs showcased their synergistic potential with other enzyme types on native biomass.
Conclusions
Bacterial GEs exhibit much larger diversity than fungal counterparts. In this study, we significantly expanded the existing knowledge on CE15 with the in-depth characterization of ten bacterial GEs broadly spanning the phylogenetic tree, and also presented two novel enzyme structures. Variations in transcriptional responses of CE15-encoding genes under different growth conditions suggest nonredundant functions for enzymes found in species with multiple CE15 genes and further illuminate the importance of GEs in native lignin–carbohydrate disassembly.

Carbohydrate esterase

Biomass conversion

Carbohydrate-active enzyme

Glucuronoyl esterase

CE15

Lignin–carbohydrate complexes

Xylan

Författare

Jenny Arnling Bååth

Chalmers, Biologi och bioteknik, Industriell bioteknik

Scott Mazurkewich

Chalmers, Biologi och bioteknik, Industriell bioteknik

Rasmus Meland Knudsen

University of Copenhagen

Jens-Christian N Poulsen

University of Copenhagen

Lisbeth Olsson

Chalmers, Biologi och bioteknik, Industriell bioteknik

Leila Lo Leggio

University of Copenhagen

Johan Larsbrink

Chalmers, Biologi och bioteknik, Industriell bioteknik

Biotechnology for Biofuels

1754-6834 (eISSN)

Vol. 11 213

Struktur-funktionstudier av enzymer som klyver bindningar mellan lignin och kolhydrater

Interreg Öresund-Kattegat-Skagerrak, 2016-12-01 -- 2017-05-31.

Interreg Öresund-Kattegat-Skagerrak, 2017-10-01 -- 2018-03-31.

Novo Nordisk Fonden, 2018-01-01 -- 2020-12-31.

Drivkrafter

Hållbar utveckling

Ämneskategorier

Biokemi och molekylärbiologi

Mikrobiologi

Strukturbiologi

Styrkeområden

Energi

Livsvetenskaper och teknik

Fundament

Grundläggande vetenskaper

DOI

10.1186/s13068-018-1213-x

Mer information

Senast uppdaterat

2018-08-31