Raman amide bands of type‐II β‐turns in cyclo‐(VPGVG)₃ and poly‐(VPGVG), and implications for protein secondary‐structure analysis

Abstract

The cyclopentadecapeptide, c(VPGVG)3, a model structure for protein type‐II β‐turns [W. J. Cook et al. (1980) J. Am. Chem. Soc. 102, 5502–5505], has been investigated by laser Raman spectroscopy. Data obtained from both normal and deuterated crystals identify amide I, III, I′, and III′ bands characteristic of the β(II)turn. The structurally related polypentapeptide poly(VPGVG) in normal and deuterated forms has also been investigated, and exhibits the same Raman amide bands as c(VPGVG)3. The coacervate of poly(VPGVG), obtained by heating the solution to 40°C, likewise exhibits a Raman spectrum very similar to that of the c(VPGVG)3 crystal. Raman spectra thus indicate closely similar secondary structures for crystalline c(VPGVG)3 and aqueous poly(VPGVG), and provide an empirical basis for interpreting the conformation sensitive amide bands of globular proteins in terms of β(II)turn structures that may be present. An important conclusion from the present findings is that the amide I Raman profile of a protein may not be sufficient in general to distinguish turns from helix and sheet secondary structures, since the major amide I peaks of the β(II)turn at 1676 and 1652 cm−1 overlap, respectively, with amide I profiles generated by β‐sheet and α‐helix conformations.

Structural investigation of the poly(pentapeptide) of elastin, poly(GVGVP), in the solid state

“…Bands of interest for this work are indicated on the figure. The first fact that called our attention was that the spectrum differed only marginally from those found in the literature on aqueous solutions of the polymer 22) . Amide Raman bands, and in general all bands in the whole spectrum, are broad and spread over a wide wavenumber range.…”

“…This group has been already used as reference band elsewhere since its spectral features (area, width, shape, etc.) seem not to be affected by experimental conditions 22) . Changes in the Amide A bandwidth were also observed (Fig.…”

“…The inserted graph shows zooms of the endothermic peak obtained for annealed samples sis nor systematic isotopic substitution has been employed up to date to assign the vibrational, Raman or IR, bands. There is only one work where the Raman spectra of aqueous solutions of this polymer were studied 22) . In this work, a tentative assignment of some bands is given.…”

Conformational Properties of Arenicins: From the Bulk to the Air–Water Interface

“…A weak splitting of this last band shows the presence of a b-turn. [18,19] After approaching the equilibrium state at the air-water interface, the band intensities do not change anymore. Comparison of inten- sities of the amide I band using s-and p-polarized light ( Figure 6) shows that the b-sheet is lying flat at the interface.…”

Mechanochemical coupling in synthetic polypeptides by modulation of an inverse temperature transition.

“…Numerous physical characterizations* have demonstrated this transition to be an inverse temperature transition, in which the order in the polypeptide part of this twocomponent system increases as the temperature is raised through the transition. Those physical characterizations include (i) self-assembly studies, in which the polypeptide is found to assemble into several-micrometer-diameter fibers composed of fibrils that in turn are composed of approximately 50-A-diameter filaments (8-10); (ii) circular dichroism and Raman spectroscopy, in which the polypeptide chains within the coacervate are seen to have a repeating p-turn conformation (11,12); (iii) nuclear Overhauser effect studies, which demonstrate the specific hydrophobic side chain associations (ref. 13, D.W.U., D. K. Chang, R. Krishna, D. H. Huang, T. L. Trapane, and K.U.P., unpublished data); (iv) NMR studies, which show a decrease in backbone mobility as the temperature is raised through the transition under conditions of constant composition (14,15); (v) dielectric relaxation studies, which show the development of an intense, localized, Debye-type relaxation near 10 MHz requiring the development of a regular dynamic backbone conformation (16); (vi) elastomer length studies, in which the elastomer shortens to less than 45% of its low-temperature length when the temperature is raised from 20'C to 40'C (17); and (vii) studies of slow thermal denaturation at 80'C in which the circular dichroism indicates the loss of order (4), composition studies show a dramatic expulsion of water to a new composition of 68% peptide and 32% water by weight (4), and, for the elastomer, there is a decrease in length and loss of elastic modulus (ref.…”