Structural insights into cellulolytic and chitinolytic enzymes revealing crucial residues of insect β-N-acetyl-D-hexosaminidase

PLoS One. 2012;7(12):e52225. doi: 10.1371/journal.pone.0052225. Epub 2012 Dec 27.

Abstract

The chemical similarity of cellulose and chitin supports the idea that their corresponding hydrolytic enzymes would bind β-1,4-linked glucose residues in a similar manner. A structural and mutational analysis was performed for the plant cellulolytic enzyme BGlu1 from Oryza sativa and the insect chitinolytic enzyme OfHex1 from Ostrinia furnacalis. Although BGlu1 shows little amino-acid sequence or topological similarity with OfHex1, three residues (Trp(490), Glu(328), Val(327) in OfHex1, and Trp(358), Tyr(131) and Ile(179) in BGlu1) were identified as being conserved in the +1 sugar binding site. OfHex1 Glu(328) together with Trp(490) was confirmed to be necessary for substrate binding. The mutant E328A exhibited a 8-fold increment in K(m) for (GlcNAc)(2) and a 42-fold increment in K(i) for TMG-chitotriomycin. A crystal structure of E328A in complex with TMG-chitotriomycin was resolved at 2.5 Å, revealing the obvious conformational changes of the catalytic residues (Glu(368) and Asp(367)) and the absence of the hydrogen bond between E328A and the C3-OH of the +1 sugar. V327G exhibited the same activity as the wild-type, but acquired the ability to efficiently hydrolyse β-1,2-linked GlcNAc in contrast to the wild-type. Thus, Glu(328) and Val(327) were identified as important for substrate-binding and as glycosidic-bond determinants. A structure-based sequence alignment confirmed the spatial conservation of these three residues in most plant cellulolytic, insect and bacterial chitinolytic enzymes.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Catalytic Domain
  • Cellulose / analogs & derivatives
  • Cellulose / metabolism*
  • Chitin / metabolism*
  • Conserved Sequence
  • Crystallography, X-Ray
  • Hydrolysis
  • Lepidoptera / enzymology*
  • Models, Molecular
  • Molecular Sequence Data
  • Mutagenesis, Site-Directed
  • Oryza / enzymology
  • Sugar Alcohols / metabolism
  • Tetroses / metabolism
  • beta-Glucosidase / chemistry
  • beta-Glucosidase / metabolism
  • beta-N-Acetylhexosaminidases / chemistry*
  • beta-N-Acetylhexosaminidases / genetics
  • beta-N-Acetylhexosaminidases / metabolism*

Substances

  • Sugar Alcohols
  • TMG-chitotriomycin
  • Tetroses
  • Chitin
  • cellotetraose
  • Cellulose
  • beta-Glucosidase
  • beta-N-Acetylhexosaminidases

Grants and funding

The authors acknowledge the financial support provided by the National Key Project for Basic Research (2010CB126100), the National Natural Science Foundation of China (31070715, 31101671), the National High Technology Research and Development Program of China (2011AA10A204), the National Key Technology R&D Program (2011BAE06B05), and the Fundamental Research Funds for the Central Universities (DUT11ZD113, DUT11RC(3)73). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.