Download MendeleyCrystal structure and site-directed mutagenesis of Bacillus macerans endo-1,3-1,4-beta-glucanase.
Hahn, M., Olsen, O., Politz, O., Borriss, R., Heinemann, U.(1995) J Biol Chem 270: 3081-3088
- PubMed: 7852389
- DOI: https://doi.org/10.1074/jbc.270.7.3081
- Primary Citation of Related Structures:
1MAC - PubMed Abstract:
In beta-glucans those beta-1,4 glycosidic bonds which are adjacent to beta-1,3 bonds are cleaved by endo-1,3-1,4-beta-glucanases (beta-glucanases). Here, the relationship between structure and activity of the beta-glucanase of Bacillus macerans is studied by x-ray crystallography and site-directed mutagenesis of active site residues. Crystal structure analysis at 2.3-A resolution reveals a jelly-roll protein structure with a deep active site channel harboring the amino acid residues Trp101, Glu103, Asp105, and Glu107 as in the hybrid Bacillus beta-glucanase H(A16-M) (Keitel, T., Simon, O., Borriss, R., and Heinemann, U. (1993) Proc. Natl. Acad. Sci. U.S.A. 90, 5287-5291). Different mutant proteins with substitutions in these residues are generated by site-directed mutagenesis, isolated, and characterized. Compared with the wild-type enzyme their activity is reduced to less than 1%. Several mutants with isosteric substitutions in Glu103 and Glu107 are completely inactive, suggesting a direct role of these residues in glycosyl bond hydrolysis. The kinetic properties of mutant beta-glucanases and the crystal structure of the wild-type enzyme are consistent with a mechanism where Glu103 and Glu107 are the catalytic amino acid residues responsible for cleavage of the beta-1,4 glycosidic bond within the substrate molecule.
Organizational Affiliation:
Forschungsgruppe Kristallographie, Max-Delbrück-Centrum für Molekulare Medizin, Berlin, Federal Republic of Germany.
