Polyproline, β‐turn helices. Novel secondary structures proposed for the tandem repeats within rhodopsin, synaptophysin, synexin, gliadin, RNA polymerase II, hordein, and gluten

Publisher Website
Google Scholar
Abstract
Seven proteins each contain 8 to 52 tandem repeats of a unique class of oligopeptide. The consensus peptide for each is rhodopsin Tyr Pro Pro Gln Gly synapto‐physin Tyr Gly Pro Gln Gly synexin Tyr Pro Pro Pro Pro Gly gliadin Tyr Pro Pro Pro Gln Pro RNA polymerase II Tyr Ser Pro Thr Ser Pro Ser hordein Phe Pro Gln Gln Pro Gln Gln Pro gluten Tyr Pro Thr Ser Pro Gln Gn Gly Tyr Although there is obvious variations of sequence and of length, the penta‐to nonapeptides share an initial Tyr(or Phe) and have high Pro contents and abundant Gly, Gln, and Ser. We have evaluated helical models that both recognize the uniqueness of these sequence repeats and accommodate variations on the basic theme. We have developed a group of related heical model for these proteins with about three oligopeptide repeats per turn of 10–20 Å. These models share several common features: Most of the ϕ dihedral angels are −54°, to accommodate Pro at all positions expect the first (Tyr). Except for the β‐turns, most ψ dihedral angles are near +140° as found in polyproline. Each oligopeptide has at least one β‐turn; several have two. Some contains a cis‐Tyr, Pro peptide bond; a few have a cis‐bond plus one β‐turn. Tyr side chains vary from totally exposed to buried within the helices and could mode to accommodate either external hydrophobic interactions or phosphorylation. The several related structures seem to be readily interconverted without major change in the overall helical parameters, and therein may lie the key to their functions.