3TTY: Crystal Structure Of Beta-galactosidase From Bacillus Circulans Sp. Alkalophilus In Complex With Galactose

Crystal structures of native and alpha-D-galactose-bound Bacillus circulans sp. alkalophilus beta-galactosidase (Bca-beta-gal) were determined at 2.40 and 2.25 A resolutions, respectively. Bca-beta-gal is a member of family 42 of glycoside hydrolases, and forms a 460 kDa hexameric structure in crystal. The protein consists of three domains, of which the catalytic domain has an (alpha/beta)(8) barrel structure with a cluster of sulfur-rich residues inside the beta-barrel. The shape of the active site is clearly more open compared to the only homologous structure available in the Protein Data Bank. This is due to the number of large differences in the loops that connect the C-terminal ends of the beta-strands to the N-terminal ends of the alpha-helices within the (alpha/beta)(8) barrel. The complex structure shows that galactose binds to the active site as an alpha-anomer and induces clear conformational changes in the active site. The implications of alpha-D-galactose binding with respect to the catalytic mechanism are discussed. In addition, we suggest that beta-galactosidases mainly utilize a reverse hydrolysis mechanism for synthesis of galacto-oligosaccharides.
PDB ID: 3TTYDownload
MMDB ID: 98154
PDB Deposition Date: 2011/9/15
Updated in MMDB: 2013/06
Experimental Method:
x-ray diffraction
Resolution: 2.25  Å
Source Organism:
Similar Structures:
Biological Unit for 3TTY: hexameric; determined by author
Molecular Components in 3TTY
Label Count Molecule
Proteins (6 molecules)
Molecule annotation
Chemicals (12 molecules)
* Click molecule labels to explore molecular sequence information.

Citing MMDB