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KMID : 0380020040190020159
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Korean Journal of Biotechnology and Bioengineering
2004 Volume.19 No. 2 p.159 ~ p.163
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Structure and Ca2+-ion effects on the Function of α-cyclodextrin Glucanotransferase from B. macerans: An X-ray study
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Choi Hee-Wook
Hong Soon-Gang
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Abstract
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The X-ray structure of the cydodextrin-glucanotransferase of Bacillus macerans was solved by molecular replacement at 2.0 resolution. The refined structure has a crystallographic R-factor of 16.6%, (Rfree/ = 20.5%). A new metal binding site occupied by two Ca2+/-ions was found at an accession channel of the active site. There is a large accumulation of negative charges that bind these Ca2+/-ions, thereby connecting segment 13-G (residue 254-276) to the main body of domain A (at H, residue 283-297). The segment 313-G contains the catalytic residue Glu258 between subsite 1 and -1 and Tyr260 (subsite 2) which is located at the entrance of the active site. The Ca2＋/-site 3a,b may have a major role for the activity and specificity of this CGTase, although it is not even conserved for the a-subclass of CGTases.
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KEYWORD
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X-ray, CGTase, crystal, molecular replacement, Ca2+-ion
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