The evolution of human SIRT1 for multi-specificity is enabled by active-site adaptation

Many enzymes that catalyze protein post translational modifications (PTM) can recognize multiple target proteins to facilitate the modification of specific residues. However, little is known regarding the molecular basis and evolution of multi-specificity in PTM catalyzing enzymes. Here, we used a combined bioinformatics-experimental approach to investigate the molecular basis for multi-specificity in human SIRT1 deacetylase. Guided by bioinformatics analysis of SIRT1 orthologues and substrate repertoire expansion, we constructed and thoroughly examined hSIRT1 variants containing two and four mutations located at the vicinity of the enzyme active site that originate from distantly related SIRT1 orthologues. We found that while these mutants maintain high activity toward conserved histone substrates, they exhibit a dramatic reduction in activity toward acetylated p53 protein that appeared late in evolution. These results demonstrate that active site substitutions in SIRT1 are essential to enable the inclusion of new substrates shedding light on on how PTM catalyzing enzymes evolve to efficiently recognize a growing number of cellular substrates.