PDBsum entry 1q4n

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Hydrolase PDB id
Protein chain
496 a.a. *
Waters ×324
* Residue conservation analysis

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Key reference
Title Structural studies of a phe256trp mutant of human salivary alpha-Amylase: implications for the role of a conserved water molecule in enzyme activity.
Authors N.Ramasubbu, K.Sundar, C.Ragunath, M.M.Rafi.
Ref. Arch Biochem Biophys, 2004, 421, 115-124. [DOI no: 10.1016/]
PubMed id 14678792
In the mechanism of hydrolysis of starch by alpha-amylases, a conserved water molecule bridging two catalytic residues has been implicated. In human salivary alpha-amylase (HSAmy), this water (W641), observed in many alpha-amylase structures, is part of a chain of water molecules. To test the hypothesis that W641 may be involved in the mechanism, Phe256 in the close vicinity was mutated to a Trp residue. X-ray structure of F256W complexed to 2-amino-2-(hydroxyethyl)-1,3-propanediol at 2.1A revealed that the water chain is disrupted. In the F256W structure exhibits a positional shift in His305, characteristic of alpha-amylase complex structures. Kinetic analysis, in comparison with HSAmy, revealed that the mutant exhibited a 70-fold decrease in the specific activity for starch and significantly reduced k(cat) (20-fold) and K(m) (4-fold) for maltoheptaoside. Collectively, these results suggest that W641 and the chain of water molecules may be critical for the alpha-amylase activity.
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