STRUCTURAL STUDY OF HUMAN GROWTH HORMONE-RELEASING FACTOR FRAGMENT-(1-29) BY VIBRATIONAL SPECTROSCOPY

The conformational structure of fragment 1-29 of human growth hormone releasing factor, hGHRF (1-29), in aqueous solution and in the solid s tate is investigated by infrared and Raman spectroscopy. The polypepti de backbone is found to be unordered in the solid state. However, the spectra of the peptide prepared as 5% (w/w) aqueous solutions show tha t approximately 28% of the peptide is involved in intermolecular beta- sheet aggregation. The remainder of the peptide exists largely as diso rdered and beta-sheet conformations with a small portion of alpha-heli ces. Tyrosine residues are found to be exposed to the solvent. The sec ondary structures are quantitatively examined through infrared spectro scopy, the conformational percentages being near those obtained by HON DA et al. [Biopolymers 31, 869 (1991)] using circular dichroism. The f ast hydrogen/deuterium exchange in peptide groups and the absence of a ny NMR sign indicative of ordered structure [G. M CLORE ei al., J. Mol ec. Biol. 191, 553 (1986)] support that the solution conformations of the non-aggregated peptide interconvert in dynamic equilibrium. Some p hysiological advantages that may derive from this conformational flexi bility are also discussed.