Simple yet functional Phosphate-loop proteins: evolution of the early protein forms

Short functional peptides are likely to have served as crucial intermediates between a primordial RNA world and the extant protein world. Our working hypothesis is that relics of these ancestral peptides still exist in the form of key motifs in active sites of present-day proteins. One such motif, probably the most obvious one, is the P-loop (Walker A motif) that typically binds the transferred phosphate moiety of ATP. Overall, our results show that P-loop NTPases could have emerged from a relatively short P-loop containing peptide and that self-assembly played a key role in endowing biochemical function despite limited size and complexity.