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The crystal structure of the 32-kDa catalytic domain of the Streptomyces
lividans xylanase A was solved by molecular isomorphous replacement methods and
subsequently refined at 2.6-A resolution to a conventional crystallographic R
factor of 0.21. This is the first successful structure determination of a member
of the F family of endo-beta-1,4-D-glycanases. Unlike the recently determined
xylanases of the G family (Wakarchuk, W. W., Campbell, R. L., Sung, W. L.,
Davoodi, J., and Yaguchi, M. (1994) Protein Sci. 3, 467-475), where the
catalytic domains have a unique beta-sheet structure, the 32-kDa domain of the
S. lividans xylanase A is folded into a complete (alpha/beta)8 barrel, the first
such fold observed among beta-1,4-D-glycanases. The active site is located at
the carbonyl end of the beta barrel. The crystal structure supports the earlier
assignment of Glu-128 and Glu-236 as the catalytic amino acids (Moreau, A.,
Roberge, M., Manin, C., Shareck, F., Kluepfel, D., and Morosoli, R. (1994)
Biochem. J., in press).
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