3vtr
Crystal Structure of insect beta-N-acetyl-D-hexosaminidase OfHex1 E328A complexed with TMG-chitotriomycin
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 PubMedThe chemical similarity of cellulose and chitin supports the idea that their corresponding hydrolytic enzymes would bind beta-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 A, 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 beta-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. Structural insights into cellulolytic and chitinolytic enzymes revealing crucial residues of insect beta-N-acetyl-D-hexosaminidase.,Liu T, Zhou Y, Chen L, Chen W, Liu L, Shen X, Zhang W, Zhang J, Yang Q PLoS One. 2012;7(12):e52225. doi: 10.1371/journal.pone.0052225. Epub 2012 Dec 27. PMID:23300622[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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