Structural and functional characterization of a promiscuous feruloyl esterase (Est1E) from the rumen bacterium Butyrivibrio proteoclasticus

Abstract

The release of polysaccharide from the plant cell wall is a key process to release the stored energy from plant biomass. Within the ruminant digestive system, a host of commensal microorganisms speed the breakdown of plant cell matter releasing fermentable sugars. The presence of phenolic compounds, most notably ferulic acid (FA), esterified within the cell wall is thought to pose a significant impediment to the degradation of the plant cell wall. The structure of a FA esterase from the ruminant bacterium Butyrivibrio proteoclasticus has been determined in two different space groups, in both the apo-form, and the ligand bound form with FA located in the active site. The structure reveals a new lid domain that has no structural homologues in the PDB. The flexibility of the lid domain is evident by the presence of three different conformations adopted by different molecules in the crystals. In the FA-bound structures, these conformations show sequential binding and closing of the lid domain over the substrate. Enzymatic activity assays demonstrate a broad activity against plant-derived hemicellulose, releasing at least four aromatic compounds including FA, coumaric acid, coumarin-3-carboxylic acid, and cinnamic acid. The rumen is a complex ecosystem that efficiently degrades plant biomass and the genome of B. proteoclasticus contains greater than 130 enzymes, which are potentially involved in this process of which Est1E is the first to be well characterized.

Cellulosilyticum ruminicola , a Newly Described Rumen Bacterium That Possesses Redundant Fibrolytic-Protein-Encoding Genes and Degrades Lignocellulose with Multiple Carbohydrate- Borne Fibrolytic Enzymes

“…Although acetyl xylan esterases are produced extensively by the ruminal bacteria and fungi, only a very limited number of described rumen bacterial species produce phenolic acid esterases. To date, feruloyl esterase activity associated with ruminal bacteria has only been confirmed for F. succinogenes, B. proteoclasticus, and P. ruminicola (15,20,30). Importantly, strain H1 produces ferulic acid esterase and three homologue genes are screened in the genome, making it one of the rare phenolic acid esterase-producing rumen bacterium identified.…”

Expression, characterization and structural modelling of a feruloyl esterase from the thermophilic fungus Myceliophthora thermophila

“…The crystal structures of FAEs, a type A AnFaeA from A. niger (PDB_ID: 1UWC, 1USW, 1UZA, 2BJH, 2IX9, 2HL6), Butyrivibrio proteoclasticus (PDB_ID: 2WTM, 2WTN) and FAE domains, XynY (PDB_ID: 1GKL) and XynZ (PDB_ID: 1JT2) of the cellulosomal enzymes included in the cellulosome complex from Clostridium thermocellum have been determined. These FAEs have a common α/ β-hydrolase fold and a catalytic triad (Ser-His-Asp) shown also in lipases (Hermoso et al 2004;Goldstone et al 2010). Type B and C FAEs have a higher level of sequence identity with AXEs and tannases, respectively (Crepin et al 2004a), which might help us understand their structure and function when crystal structures are obtained.…”

Three Feruloyl Esterases in Cellulosilyticum ruminicola H1 Act Synergistically To Hydrolyze Esterified Polysaccharides

“…On the basis of their primary sequences and substrate specificity against four model substrates, methyl ferulate (MFA), methyl caffeate (MCA), methyl p-coumarate (MpCA), and methyl sinapate (MSA), Faes are classified as types A, B, C, and D (8,36). Despite having various primary amino acid sequences, Faes share similar three-dimensional structures, with an ␣/␤-hydrolase having a serine, histidine, and aspartic acid catalytic triad (22,26,38).…”