Sandbox Reserved 459: Difference between revisions

To examine the crystal structure of human salivary amylase, X-ray crystallography was used with a resolution of 1.60 Å.  The active site of alpha-amylase contains a trio of acidic groups that do most of the work. Ca2+ is a common <scene name='Sandbox_Reserved_459/Christie_ligand/1'>ligand</scene> for alpha amylase.The Ca2+ ion is bound to Asnl00, Arg158, Asp167, His201 and three water molecules. The Cl- ion is bound to Arg195, Asn298 and Arg337 and one water molecule. The highly mobile glycine-rich loop 304-310 may act as a gateway for substrate binding and be involved in a `trap-release' mechanism in the hydrolysis of substrates. Strategic placement of calcium and chloride ions, as well as histidine and tryptophan residues may play a role in differentiating between the glycone and aglycone ends of the polysaccharide substrates. Salivary amylase also possesses a suitable site for binding to enamel surfaces and provides potential sites for the binding of bacterial adhesins. . Salivary amylase folds into a multidomain structure consisting of three domains, A, B and C. Domain A has a (a/b)8- barrel structure, domain B has no definite topology and domain C has a Greek-key barrel structure. Circular dichroism spectroscopic data revealed the native alpha-amylase to contain 25% <scene name='Sandbox_Reserved_459/Christie_helix/1'>alpha helix</scene>, 21% <scene name='Sandbox_Reserved_459/Christie_beta_sheet/1'>beta sheet</scene>, and 54% random coils. It is generally assumed that in proteins hydrophobic residues are not favorable at solvent-exposed sites, and that amino acid substitutions on the surface have little effect on protein thermostability. Contrary to these assumptions, hyperthermostable variants of alpha amylase have been identified that result from the incorporation of <scene name='Sandbox_Reserved_459/Christie_hydrophobic/1'>hydrophobic residues</scene> at the surface.