Statistical Evidence for a Helical Nascent Chain

We investigate the hypothesis that protein folding is a kinetic, non-equilibrium process, in which the structure of the nascent chain is crucial. We compare actual amino acid frequencies in loops, [Formula: see text]-helices and [Formula: see text]-sheets with the frequencies that would arise in the absence of any amino acid bias for those secondary structures. The novel analysis suggests that while specific amino acids exist to drive the formation of loops and sheets, none stand out as drivers for [Formula: see text]-helices. This favours the idea that the [Formula: see text]-helix is the initial structure of most proteins before the folding process begins.