Chemistry Reference
In-Depth Information
in phosphate buffer (pH 7.4) and dimethylsulfoxide (DMSO) were tested for the
formation of long fibers. Gel permeation chromatography analysis determined that
polymerization of (Pro-Hyp-Gly)
5
and (Pro-Hyp-Gly)
10
at a concentration of 2.5
mg/mL in DMSO resulted in the formation of high molecular weight products
exceeding 10000 kDa. However, the same peptides yielded products of low
molecular weights when the reactions were carried out in phosphate buffer. Of
interest, polymerization of Pro-Hyp-Gly at a high concentration (50 mg/mL) in phos-
phate buffer produced polypeptides with molecular weights over 10000 kDa. CD
analysis showed that (Pro-Hyp-Gly)
5
and (Pro-Hyp-Gly)
10
formed more stable
triple helices in less polar solvent than in phosphate buffer, whereas Pro-Hyp-Gly
did not self-assemble into triple helices in either solvents. This result suggests
that preorganization prior to the polymerization lowers the activation energy of the
reaction. Polycondensation of Pro-Hyp-Gly only proceeds at high concentration,
because the probability of head-tail intermolecular polycondensation significantly
increases. Under TEM, poly(Pro-Hyp-Gly)
10
displayed nanofibers microns in
length with a 10-nm diameter, which corresponds to a bundle of about 30 aggregated
triple helical chains (Fig. 14.12).
Our group demonstrated an approach involving covalently coupling short peptides
to create extended collagen-like peptide polymers by native chemical ligation
(Paramonov et al. 2005). Native chemical ligation features the ability to couple
two unprotected peptides with a thioester at the C-terminus and a cysteine at the
N-terminus. Thioester linkage and subsequent intramolecular reaction forms a
native peptide bond between the two peptides. Three peptides were synthesized;
each was 30 amino acids long with a Pro-Hyp-Gly repeat and cysteine at the
N-terminus followed by the conversion of the C-terminus into an activated thioester.
Figure 14.12 Fibers formed by polycondensation of (Pro-Hyp-Gly)
10
. Reprinted from
Kishimoto et al. (2005). Copyright 2005 Wiley InterScience.
