1KWG

Crystal structure of Thermus thermophilus A4 beta-galactosidase

Summary for 1KWG

• Entry DOI: 10.2210/pdb1kwg/pdb
• Descriptor: BETA-GALACTOSIDASE, CHLORIDE ION, ACETATE ION, ... (6 entities in total)
• Functional Keywords: tim barrel, glycoside hydrolase family 42, trimer, hydrolase
• Biological source: Thermus thermophilus
• Total number of polymer chains: 1
• Total formula weight: 73364.22

Authors

Hidaka, M.,Fushinobu, S.,Ohtsu, N.,Motoshima, H.,Matsuzawa, H.,Shoun, H.,Wakagi, T. (deposition date: 2002-01-29, release date: 2002-09-18, Last modification date: 2024-03-13)

Primary citation

Hidaka, M.,Fushinobu, S.,Ohtsu, N.,Motoshima, H.,Matsuzawa, H.,Shoun, H.,Wakagi, T.
Trimeric Crystal Structure of the Glycoside Hydrolase Family 42 beta-Galactosidase from Thermus thermophilus A4 and the Structure of its Complex with Galactose
J.MOL.BIOL., 322:79-91, 2002

PubMed Abstract: The beta-galactosidase from an extreme thermophile, Thermus thermophilus A4 (A4-beta-Gal), is thermostable and belongs to the glycoside hydrolase family 42 (GH-42). As the first known structures of a GH-42 enzyme, we determined the crystal structures of free and galactose-bound A4-beta-Gal at 1.6A and 2.2A resolution, respectively. A4-beta-Gal forms a homotrimeric structure resembling a flowerpot. Each monomer has an active site located inside a large central tunnel. The N-terminal domain of A4-beta-Gal has a TIM barrel fold, as predicted from hydrophobic cluster analysis. The putative catalytic residues of A4-beta-Gal (Glu141 and Glu312) superimpose well with the catalytic residues of Escherichia coli beta-galactosidase. The environment around the catalytic nucleophile (Glu312) is similar to that in the case of E.coli beta-galactosidase, but the recognition mechanism for a substrate is different. Trp182 of the next subunit of the trimer constitutes a part of the active-site pocket, indicating that the trimeric structure is essential for the enzyme activity. Structural comparison with other glycoside hydrolases revealed that many features of the 4/7 superfamily are conserved in the A4-beta-Gal structure. On the basis of the results of 1H NMR spectroscopy, A4-beta-Gal was determined to be a "retaining" enzyme. Interestingly, the active site was similar with those of retaining enzymes, but the overall fold of the TIM barrel domain was very similar to that of an inverting enzyme, beta-amylase.

PubMed: 12215416
DOI: 10.1016/S0022-2836(02)00746-5

Experimental method

X-RAY DIFFRACTION (1.6 Å)