Crystal structure of a bacterial chitinase at 2.3 A resolution.
BACKGROUND
Chitinases cleave the beta-1-4-glycosidic bond between the N-acetyl-D-glucosamine units of which chitin is comprised. Chitinases are present in plants, bacteria and fungi, but whereas structures are available for two prototypic plant enzymes, no structure is available for a bacterial or fungal chitinase.


RESULTS
To redress this imbalance, the structure of native chitinase A from Serratia marcescens has been solved by multiple isomorphous replacement and refined at 2.3 A resolution, resulting in a crystallographic R-factor of 16.2%. The enzyme comprises three domains: an all beta-strand amino-terminal domain, a catalytic alpha/beta-barrel domain, and a small alpha+beta-fold domain. There are several residues with unusual geometries in the structure. Structure determination of chitinase A in complex with N,N',N",N"'-tetra-acetylo-chitotetraose, together with biochemical and sequence analysis data, enabled the positions of the active-site and catalytic residues to be proposed.


CONCLUSIONS
The reaction mechanism seems to be similar to that of lysozyme and most other glycosylhydrolases, i.e. general acid-base catalysis. The role of the amino-terminal domain could not be identified, but it has similarities to the fibronectin III domain. This domain may possibly facilitate the interaction of chitinase A with chitin.
Perrakis
A
A
European Molecular Biology Laboratory, Hamburg, Germany.
Tews
I
I
Dauter
Z
Z
Oppenheim
A B
AB
Chet
I
I
Wilson
K S
KS
Vorgias
C E
CE
D000595:Amino Acid Sequence; D001483:Base Sequence; D001665:Binding Sites; D002688:Chitinases / Q000737:chemistry*; D004269:DNA, Bacterial; D004583:Electrons; D008969:Molecular Sequence Data; D011487:Protein Conformation; D016415:Sequence Alignment; D012706:Serratia marcescens / Q000201:enzymology*
D004269:DNA, Bacterial; D002688:Chitinases