Evaluation of Porcine and Aspergillus oryzae alpha-Amylases as Possible Model for the Human Enzyme

alpha-amylases are ubiquitous enzymes belonging to the glycosyl hydrolase (GH13) family, whose members share a high degree of sequence identity, even between distant organisms. To understand the determinants of catalytic activity of alpha-amylases throughout evolution, and to investigate the use of homologous enzymes as a model for the human one, we compared human salivary alpha-amylase, Aspergillus oryzae alpha-amylase and pancreatic porcine alpha-amylase, using a combination of in vitro and in silico approaches. Enzyme sequences were aligned, and structures superposed, whereas kinetics were spectroscopically studied by using commercial synthetic substrates. These three enzymes show strikingly different activities, specifically mediated by different ions, despite relevant structural homology. Our study confirms that the function of alpha-amylases throughout evolution has considerably diverged, although key structural determinants, such as the catalytic triad and the calcium-binding pocket, have been retained. These functional differences need to be carefully considered when alpha-amylases, from different organisms, are used as a model for the human enzymes. In this frame, particular focus is needed for the setup of proper experimental conditions.