Structural highlights
Publication Abstract from PubMedChitin, a beta-1,4-linked homopolysaccharide of N-acetyl-d-glucosamine (GlcNAc), is one of the most abundant biopolymers on Earth. Paenibacillus sp. str. FPU-7 produces several different chitinases and converts chitin into N,N'-diacetylchitobiose ((GlcNAc)2) in the culture medium. However, the mechanism by which the Paenibacillus species imports (GlcNAc)2 into the cytoplasm and divides it into the monomer GlcNAc remains unclear. The gene encoding Paenibacillus beta-N-acetyl-d-glucosaminidase (PsNagA) was identified in the Paenibacillus sp. str. FPU-7 genome using an expression cloning system. The deduced amino acid sequence of PsNagA suggests that the enzyme is a part of the glycoside hydrolase family 3 (GH3). Recombinant PsNagA was successfully overexpressed in Escherichia coli and purified to homogeneity. As assessed by gel permeation chromatography, the enzyme exists as a 57-kDa monomer. PsNagA specifically hydrolyses chitin oligosaccharides, (GlcNAc)2-4, 4-nitrophenyl N-acetyl beta-d-glucosamine (pNP-GlcNAc) and pNP-(GlcNAc)2-6, but has no detectable activity against 4-nitrophenyl beta-d-glucose, 4-nitrophenyl beta-d-galactosamine and colloidal chitin. In this study, we present a 1.9 A crystal structure of PsNagA bound to GlcNAc. The crystal structure reveals structural features related to substrate recognition and the catalytic mechanism of PsNagA. This is the first study on the structural and functional characterization of a GH3 beta-N-acetyl-d-glucosaminidase from Paenibacillus sp. Structural and functional characterization of a glycoside hydrolase family 3 beta-N-acetylglucosaminidase from Paenibacillus sp. str. FPU-7.,Itoh T, Araki T, Nishiyama T, Hibi T, Kimoto H J Biochem. 2019 Dec 1;166(6):503-515. doi: 10.1093/jb/mvz072. PMID:31501879[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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