Molecular characterization of α-amylase from Staphylococcus aureus

Staphylococcus aureus is one of the prominent Gram positive human pathogen secretes many surface and secretary proteins including various enzymes and pathogenic factors that favour the successful colonization and infection of host tissue. α-amylase is one of the enzymes secreted by S. aureus which catalyses the breakdown of complex sugars to monosaccharides, which are required for colonization and survival of this pathogen in any anatomical locales. In the present study we have cloned, sequenced, expressed and characterized α-amylase gene from S. aureus ATCC12600. The recombinant enzyme has a molecular weight of 58kDa and the kinetics showed Vmax 0.0208±0.033 (mg/ml)/mg/min and Km 10.633±0.737mg/ml. The multiple sequence analysis showed α-amylase of S. aureus exhibited large differences with Bacillus subtilis and Streptococcus bovis. As the crystal structure of S. aureus α-amylase was unavailable, we used homology modelling method to build the structure. The built structure was validated by Ramachandran plot which showed 90% of the residues in the allowed region while no residue was found in the disallowed region and the built structure was close to the crystal structure with Z-Score: -6.85. The structural superimposition studies with α-amylases of Bacillus subtilis and Streptococcus bovis showed distinct differences with RMSD values of 18.158 and 7.091 respectively which correlated with enzyme kinetics, indicating α-amylase is different among these bacteria.