3nsm | pdb_00003nsm
Crystal Structure of insect beta-N-acetyl-D-hexosaminidase OfHex1 from Ostrinia furnacalis
Structural highlights
FunctionHEXC_OSTFU Hydrolyzes one beta-GlcNAc unit at a time from the non-reducing ends of substrates, with a preference for shorter substrates. The 2-acetamido group and the beta-glycoside bond linkage in the substrate are required for its activity. Active with p-nitrophenyl (pNP)-beta-GlcNAc, pNP-beta-GalNAc and chitooligosaccharides (degree of polymerization from 2 to 6), but not with the complex N-glycan substrate (GlcNAcbeta-1,2Manalpha-1,6)(GlcNAcbeta-1,2Manalpha-1,3)Manbeta-1,4GlcNAcbeta-1,4GlcNAc-PA (GnGn-PA), pNP-alpha-GlcNAc or with the long polymer colloidal chitin. Involved in chitin catabolism (PubMed:18959754). Involved in the degradation of old cuticle during the pupation stage (PubMed:21106526).[1] [2] Publication Abstract from PubMedbeta-N-Acetyl-d-hexosaminidase has been postulated to have a specialized function. However, the structural basis of this specialization is not yet established. OfHex1, the enzyme from the Asian corn borer Ostrinia furnacalis (one of the most destructive pests) has previously been reported to function merely in chitin degradation. Here the vital role of OfHex1 during the pupation of O. furnacalis was revealed by RNA interference, and the crystal structures of OfHex1 and OfHex1 complexed with TMG-chitotriomycin were determined at 2.1 A. The mechanism of selective inhibition by TMG-chitotriomycin was related to the existence of the +1 subsite at the active pocket of OfHex1 and a key residue, Trp(490), at this site. Mutation of Trp(490) to Ala led to a 2,277-fold decrease in sensitivity toward TMG-chitotriomycin as well as an 18-fold decrease in binding affinity for the substrate (GlcNAc)(2). Although the overall topology of the catalytic domain of OfHex1 shows a high similarity with the human and bacterial enzymes, OfHex1 is distinguished from these enzymes by large conformational changes linked to an "open-close" mechanism at the entrance of the active site, which is characterized by the "lid" residue, Trp(448). Mutation of Trp(448) to Ala or Phe resulted in a more than 1,000-fold loss in enzyme activity, due mainly to the effect on k(cat). The current work has increased our understanding of the structure-function relationship of OfHex1, shedding light on the structural basis that accounts for the specialized function of beta-N-acetyl-d-hexosaminidase as well as making the development of species-specific pesticides a likely reality. Structural Determinants of an Insect {beta}-N-Acetyl-D-hexosaminidase Specialized as a Chitinolytic Enzyme.,Liu T, Zhang H, Liu F, Wu Q, Shen X, Yang Q J Biol Chem. 2011 Feb 11;286(6):4049-58. Epub 2010 Nov 24. PMID:21106526[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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