0 avis
Structure-Function characterization of a GH43 enzyme found in a Polysaccharide Utilization Locus of termite gut microbiota Authors
Archive ouverte
Edité par CCSD -
International audience. Xylosidases (EC 3.2.1.37) are involved in the final step of hemicelluloses deconstructionby microorganisms, catalyzing the hydrolysis of xylooligosaccharides resulting fromxylanases action. Xylosidases belong to the GH43 family according to the CAZyclassification, one of the largest GH families. It is divided into 37 sub-families accordingto the structure and the substrate specificity. Members of this family showed anenzymatic inverting mechanism [1]. Based on crystal structure and molecular modelinganalysis, previous work suggested the crucial role of divalent ions in optimal hydrolysisactivity of GH43, especially calcium ions [2]. In this work, we describe an atypical GH43enzyme (Pm21) found in Pseudacanthotermes militaris termite gut metagenome [3].This enzyme belongs to a xylan utilization system, encoding three xylanases (two GH10and one GH11), a carbohydrate esterase (CE1), a glucuronidase (GH115) and axylosidase (Pm21). Phylogenetic analysis showed that Pm21 is distantly related topreviously characterized GH43 subfamily1 enzymes. Moreover, amino acids involved inmetal binding are weakly conserved in Pm21. Biochemical characterization showed thatthe enzyme favors magnesium over calcium for its activity. Indeed, magnesium iscrucial for the enzyme activity and leads to a high improvement of the catalytic activitywhile decreasing its melting temperature. The enzyme displayed an optimal activity at30°C and pH 7.0 and the catalytic efficiency values (kcat/KM) for pNP-xylopyranosideand xylobiose were 427.6 and 2742.5 min-1.mM-1, respectively. Compared to othersGH43 subfamily 1 enzymes, Pm21 is the most efficient enzyme described in thissubfamily [4,5]. In addition to the biochemical characterization, we present the structureof Pm21 solved with xylose molecule in the active site and magnesium ions in the metalbinding site. Altogether, our results suggest that the destabilization of the protein leads118to improve its activity. To our knowledge, this unusual behaviour was not reported beforein the Family GH43.
Consulter en ligne
Suggestions
Du même auteur
