標題: Exploration of glycosyl hydrolase family 75, a chitosanase from Aspergillus fumigatus
作者: Cheng, CY
Chang, CH
Wu, YJ
Li, YK
交大名義發表
應用化學系
National Chiao Tung University
Department of Applied Chemistry
公開日期: 10-二月-2006
摘要: A powerful endo-chitosanase ( CSN) previously described for a large scale preparation of chito-oligosaccharides ( Cheng, C.-Y., and Li, Y.-K. ( 2000) Biotechnol. Appl. Biochem. 32, 197 - 203) was cloned from Aspergillus fumigatus and further identified as a member of glycosyl hydrolase family 75. We report here a study of gene expression, functional characterization, and mutation analysis of this enzyme. Gene cloning was accomplished by reverse transcription-PCR and inverse PCR. Within the 1382-bp Aspergillus gene ( Gen-Bank (TM) accession number AY190324), two introns ( 67 and 82 bp) and an open reading frame encoding a 238-residue protein containing a 17-residue signal peptide were characterized. The recombinant mature protein was overexpressed as an inclusion body in Escherichia coli, rescued by treatment with 5 M urea, and subsequently purified by cation exchange chromatography. A time course H-1 NMR study on the enzymatic formation of chito-oligosaccharides confirmed that this A. fumigatus CSN is an inverting enzyme. Tandem mass spectrum analysis of the enzymatic hydrolysate revealed that the recombinant CSN can cleave linkages of GlcNAc-GlcN and GlcN-GlcN in its substrate, suggesting that it is a subclass I chitosanase. In addition, an extensive site-directed mutagenesis study on 10 conserved carboxylic amino acids of glycosyl hydrolase family 75 was performed. This showed that among these various mutants, D160N and E169Q lost nearly all activity. Further investigation using circular dichroism measurements of D160N, E169Q, wild-type CSN, and other active mutants showed similar spectra, indicating that the loss of enzymatic activity in D160N and E169Q was not because of changes in protein structure but was caused by loss of the catalytic essential residue. We conclude that Asp(160) and Glu(169) are the essential residues for the action of A. fumigatus endo-chitosanase.
URI: http://dx.doi.org/10.1074/jbc.M512506200
http://hdl.handle.net/11536/149068
ISSN: 0021-9258
DOI: 10.1074/jbc.M512506200
期刊: JOURNAL OF BIOLOGICAL CHEMISTRY
Volume: 281
起始頁: 3137
結束頁: 3144
顯示於類別:期刊論文