Gw. Harris et al., REFINED CRYSTAL-STRUCTURE OF THE CATALYTIC DOMAIN OF XYLANASE-A FROM PSEUDOMONAS-FLUORESCENS AT 1.8 ANGSTROM RESOLUTION, Acta crystallographica. Section D, Biological crystallography, 52, 1996, pp. 393-401
Citations number
41
Categorie Soggetti
Crystallography,"Biochemical Research Methods",Biology
The three-dimensional structure of native xylanase A from Pseudomonas
fluorescens subspecies cellulosa has been refined at 1.8 Angstrom reso
lution. The space group is P2(1)2(1)2(1) with four molecules in the as
ymmetric unit. The final model has an R factor of 0.166 for 103 749 re
flections with the four molecules refined independently. The tertiary
structure consists of an eightfold beta/alpha-barrel, the so-called TI
M-barrel fold. The active site is in an open cleft at the carboxy-term
inal end of the beta/alpha-barrel, and the active-site residues are a
pair of glutamates, Glu127 on strand 4 and Glu246 on strand 7. Both th
ese catalytic glutamate residues are found on beta-bulges. An atypical
ly long loop after strand 7 is stabilized by calcium. Unusual features
include a non-proline cis-peptide residue Ala80 which is found on a b
eta-bulge at the end of beta-strand 3. The three beta-bulge type disto
rtions occurring on beta-strands 3, 4 and 7 are functionally significa
nt as they serve to orient important active-site residues. The active-
site residues are further held in place by an extensive hydrogen-bondi
ng network of active-site residues in the catalytic site of xylanase A
. A chain of well ordered water molecules occupies the substrate-bindi
ng cleft, some or all of which are expelled on binding of the substrat
e.