H. Sugano

Prolyl hydroxylation of the polypentapeptide model of elastin impairs fiber formation

Abstract With elastogenesis described as a process dominated by intermolecular hydrophobic interactions and the polypentapeptide, (Val-Pro-Gly)Val-Gly)n, presented as a model for the dominant dynamic elements of the elastic fiber, it is demonstrated that hydroxylation of proline residues of the polypentapeptide unfavorably affects the inverse temperature transition leading to fiber formation such that even with only 10% of the proline residues hydroxylated very little fiber formation occurs at 37°C. Significantly higher temperatures are required. As prolyl hydroxylase, elaborated during a fibrogenic response, hydroxylates elastin, this result raises the question as to whether hydroxylation of the precursor protein of the elastic fiber may similarly impair in vivo fiber formation.

Nuclear magnetic resonance studies on a cyclic dodecapeptide analogue of a repeat hexapeptide of tropoelastin: evaluation of secondary structure.

The cyclododecapeptide, (Ala1-Pro2-Gly3-Val4-Gly5-Val6)2, was synthesized and its secondary structure was evaluated from extensive studies in dimethyl sulphoxide, trifluoroethanol and water using NMR methods. A selective decoupling technique in 13C-NMR has been utilized in order to assign the C=O carbon resonances. Temperature dependence of the peptide NH protons and the solvent perturbation of the peptide NH and C=O resonances show the occurrence in all solvents of a beta-turn (a 10-membered H-bond between the Val4 NH and Ala1 C=O) and a gamma-turn, an 11-membered H-bond between the Gly3 NH and the Gly5 C=O; and a possible 14-membered H-bond between the Ala1 NH and the Val4 C=O in dimethyl sulphoxide and trifluoroethanol. These secondary structural features are compared with the linear polyhexapeptide and found the the beta-turn and the gamma-turn are the common conformational features of these peptide systems.

Conformational study of the cyclic hexapeptide L-Ala-L-Pro-Gly-L-Val-Gly-L-Val, by nuclear magnetic resonance spectroscopy

The cyclohexapeptide [graphic omitted] has been synthesized and its conformational features have been derived from n.m.r. parameters in chloroform. The nuclear Overhauser effect (n.O.e) has been used to distinguish between the two glycine and valine residues in the molecule. 13C Spin–lattice relaxation times (T1) have been measured and an average T1 value of 189 ms with a range of 158–202 ms for the α-carbon atoms has been obtained, which is indicative of a relatively rigid molecule. The n.O.e. and the geminal coupling constants [2J] and 3J(NH–αCH) have been utilized to obtain an estimation of the torison angles ψ and ϕ. Two β-turns, formed between the Ala1 NH and the Val4(CO (type II′) and the Val4 NH and the Ala1 CO (type II), are proposed. The conformational properties of this cyclic molecule are discussed in relation to the conformational features of its linear counterpart.

Nuclear magnetic resonance and conformational energy calculations of repeat peptides of tropoelastin: conformational characterization of the cyclododecapeptide

N.m.r. data obtained in chloroform–dimethyl sulphoxide solutions and conformational-energy calculations are reported which deduce the preferred conformation of the cyclic dodecapeptide, cyclo-(L-Ala1-L-Pro2-Gly3-L-Val4-Gly5-L-Val6)2, having the hexapeptide repeat sequence of tropoelastin. The non-equivalence of the Gly α-CH2 protons and the similarity of α-carbon relaxation times indicate that the molecule is quite rigid. The 1H n.m.r. spectrum of the molecule resembles that of a hexamer, indicating that the molecule possesses two-fold symmetry on the n.m.r. time scale. The possible ranges of backbone torsion angles except ψ(Ala1) are derived from α-CH–NH coupling constants, geminal coupling constants, and nuclear Overhauser effects. From temperature-dependence studies of the peptide NH chemical shift and from the coupling constants, secondary structural features of the molecule are obtained. The valyl α-CH–β-CH coupling constants show that the Val4 side chain is in a gauche conformation, while the Val6 side chain is in the trans-conformation. A static wire model is developed using these data and containing the following solution-derived hydrogen bonds: CO(1)⋯ HN(4)(β-turn), NH(1)⋯ OC(4) and NH(6)⋯ OC(4)(bifurcated 14- and 17-membered rings), and NH(3)⋯ OC(5)(γ-turn). In vacuo conformational-energy calculations are performed to obtain several minimum-energy conformations. The theoretical calculations utilize the Go–Scheraga method for cyclization with exact two-fold symmetry. Only one of the low-energy structures so obtained is consistent with all the experimental data, and this structure is quite similar to the static wire model based on the n.m.r. data.