Synthesis of peptides and glycopeptides with polyproline II helical topology as potential antifreeze molecules.

A library of peptides and glycopeptides containing (4R)-hydroxy-L-proline (Hyp) residues were designed with a view to providing stable polyproline II (PPII) helical molecules with antifreeze activity. A library of dodecapeptides containing contiguous Hyp residues or an Ala-Hyp-Ala tripeptide repeat sequence were synthesized with and without α-O-linked N-acetylgalactosamine and α-O-linked galactose-ß-(1→3)-N-acetylgalactosamine appended to the peptide backbone. All (glyco)peptides possessed PPII helical secondary structure with some showing significant thermal stability. The majority of the (glyco)peptides did not exhibit thermal hysteresis (TH) activity and were not capable of modifying the morphology of ice crystals. However, an unglycosylated Ala-Hyp-Ala repeat peptide did show significant TH and ice crystal re-shaping activity suggesting that it was capable of binding to the surface of ice. All (glyco)peptides synthesized displayed some ice recrystallization inhibition (IRI) activity with unglycosylated peptides containing the Ala-Hyp-Ala motif exhibiting the most potent inhibitory activity. Interestingly, although glycosylation is critical to the activity of native antifreeze glycoproteins (AFGPs) that possess an Ala-Thr-Ala tripeptide repeat, this same structural modification is detrimental to the antifreeze activity of the Ala-Hyp-Ala repeat peptides studied here.

Synthesis and protein binding studies of a peptide fragment of clathrin assembly protein AP180 bearing an O-linked ß-N-acetylglucosaminyl-6-phosphate modification.

A novel post-translational modification of threonine, ß-N-acetylglucosaminyl-phosphate, was recently discovered on assembly protein AP180, a protein which plays a crucial role in clathrin coated vesicle formation in synaptic vesicle endocytosis (SVE). Herein, we report studies aimed at probing the effect of this modification on binding to proteins in rat brain lysate using pull down experiments with peptide fragments of AP180.