2QPS

"Sugar tongs" mutant Y380A in complex with acarbose

Summary for 2QPS

• Entry DOI: 10.2210/pdb2qps/pdb
• Related: 1AMY 1HT6 1P6W 1RP8 1RP9 1RPK 2QPU
• Descriptor: Alpha-amylase type A isozyme, CALCIUM ION (3 entities in total)
• Functional Keywords: beta alpha 8 barrel, sugar tongs complex, calcium, carbohydrate metabolism, germination, glycosidase, hydrolase, metal-binding, secreted
• Biological source: Hordeum vulgare
• Cellular location: Secreted, extracellular space: P00693
• Total number of polymer chains: 1
• Total formula weight: 44668.19

Authors

Aghajari, N.,Jensen, M.H.,Tranier, S.,Haser, R. (deposition date: 2007-07-25, release date: 2008-02-12, Last modification date: 2023-08-30)

Primary citation

Bozonnet, S.,Jensen, M.T.,Nielsen, M.M.,Aghajari, N.,Jensen, M.H.,Kramhoft, B.,Willemoes, M.,Tranier, S.,Haser, R.,Svensson, B.
The 'pair of sugar tongs' site on the non-catalytic domain C of barley alpha-amylase participates in substrate binding and activity
Febs J., 274:5055-5067, 2007

PubMed Abstract: Some starch-degrading enzymes accommodate carbohydrates at sites situated at a certain distance from the active site. In the crystal structure of barley alpha-amylase 1, oligosaccharide is thus bound to the 'sugar tongs' site. This site on the non-catalytic domain C in the C-terminal part of the molecule contains a key residue, Tyr380, which has numerous contacts with the oligosaccharide. The mutant enzymes Y380A and Y380M failed to bind to beta-cyclodextrin-Sepharose, a starch-mimic resin used for alpha-amylase affinity purification. The K(d) for beta-cyclodextrin binding to Y380A and Y380M was 1.4 mm compared to 0.20-0.25 mm for the wild-type, S378P and S378T enzymes. The substitution in the S378P enzyme mimics Pro376 in the barley alpha-amylase 2 isozyme, which in spite of its conserved Tyr378 did not bind oligosaccharide at the 'sugar tongs' in the structure. Crystal structures of both wild-type and S378P enzymes, but not the Y380A enzyme, showed binding of the pseudotetrasaccharide acarbose at the 'sugar tongs' site. The 'sugar tongs' site also contributed importantly to the adsorption to starch granules, as Kd = 0.47 mg.mL(-1) for the wild-type enzyme increased to 5.9 mg.mL(-1) for Y380A, which moreover catalyzed the release of soluble oligosaccharides from starch granules with only 10% of the wild-type activity. beta-cyclodextrin both inhibited binding to and suppressed activity on starch granules for wild-type and S378P enzymes, but did not affect these properties of Y380A, reflecting the functional role of Tyr380. In addition, the Y380A enzyme hydrolyzed amylose with reduced multiple attack, emphasizing that the 'sugar tongs' participates in multivalent binding of polysaccharide substrates.

PubMed: 17803687
DOI: 10.1111/j.1742-4658.2007.06024.x

Experimental method

X-RAY DIFFRACTION (2.2 Å)