Disulfide Bond Dihedral Angles from Raman Spectroscopy

Abstract

Raman spectra of several compounds containing the CS-SC moiety were obtained (in the solid phase) from 450-800 cm-' to investigate the S-S and C-S stretching behavior. The S-S stretching frequency varied linearly with the CS-SC dihedral angle (obtained from either x-ray or neutron diffraction or ultraviolet absorption) for compounds whose CC-SS dihedral angles were not very different. The ratio of the intensities of the S-S and C-S stretching bands exhibited no recognizable correlation with either the CS-SC dihedral angle or the CSS bond angle, probably because this ratio is sesisitive to the crystalline environment. The linear dependence of the S-S stretching frequency on dihedral angle leads to a dihedral angle for the plant hormone, malformin A, that is in excellent agreement with that estimated from the longest wavelength CS-SC ultraviolet absorption band.The disulfide bond is an important structural feature of many important biological molecules. The CS-SC moiety occurs in antibiotics such as gliotoxin, sporidesmin, and acetylaranotin in the form of an S-S bridged piperazinedione system in which the CS-SC dihedral angle is severely restricted by ring closure (1, 2). Hormones, such as oxytocin (3), vasopressin (4), and malformin (5), contain disulfide bonds (cystine) that can assume conformations with widely varying dihedral angle, depending upon ring size and other structural constraints. In globular proteins, such as ribonuclease, chymotrypsin, lysozyme, carboxypeptidase, etc., packing requirements may result in dihedral angles that vary substantially from the widely accepted value (6) of about 900 for L-cystine in aqueous solution. In chymotrypsin, for example, this angle varies from 87°-126°(7). It is, therefore, of considerable importance to have a method that can provide information about this dihedral angle both in solid state and in aqueous solution. Raman spectroscopy appears to be a suitable technique for this purpose, since the Raman spectra of compounds containing disulfide bonds usually show welldefined bands that arise from C-S and S-S stretching modes (8,9), and these vibrations might be sensitive to the CS-SC dihedral angle.Absorption spectra can also be used to obtain information about CS-SC dihedral angles, since the relationship between this dihedral angle and the longest-wavelength CS-SC absorption frequency in the ultraviolet is well established both theoretically (10) and experimentally (see references cited in ref. 10). However, this method for determining CS-SC dihedral angles is limited to simple systems in which the UV absorption spectrum is free from nondisulfide-related transitions from about 250 to 380 nm. Many systems (proteins for example, which contain aromatic residues) have nondisulfide chromophores that absorb in this region, and thus prevent study of the CS-SC absorption bands. On the other hand, as t To whom requests for reprints should be addressed. 2619has been pointed out (8, 9), these compounds (including proteins) exhibit S-S and C-S stretching bands in a reg...

Role of ionic liquids in protein refolding: native/fibrillar versus treated lysozyme

“…43,44 As shown in Fig. 3, the four S-S bridges in native lysozyme give rise to three Raman bands at 507, 526 and 540 cm -1 indicating that the intra-molecular S-S bonds in native lysozyme are in GGG, GGT and TGT conformations,45 in agreement with the results of Van Wart et al 29 After fibril formation, the intensities of υ(S-S) vibrations near 530 and 540 cm -1 disappeared, clearly indicating a distortion of the dihedral angles with respect to the native structure. On the other side, the C-C-N stretching peaks are centered around 930 cm -1 when the protein structure is mainly α helix and at higher frequencies (around 960-980 cm -1 ) when it is mainly in a β sheet conformation (see the vertical dashed lines in Fig.…”

Stable conformations of aliphatic disulfides: influence of 1,4 interactions involving sulfur atoms.

“…This is confirmed by the results of x-ray crystallographic studies (summarized in refs. 4,6, and 7), and by gas phase electron diffraction (9,10) (1). The value of v(S-S) observed for strained disulfides can be used to estimate the value of lx(CS-SC)I (7,8).…”

“…In a recent series of papers (1)(2)(3)(4)(5)(6)(7)(8) from this laboratory, various experimental and theoretical techniques were used to study the conformations of aliphatic disulfides structurally related to cystine. On the basis of these studies, it was suggested that there exist weak attractive interactions between CH groups and S atoms that are separated by three intervening single bonds.…”

Enhancing protein stability with extended disulfide bonds

“…There has been considerable success in the use of structure-based design to engineer disulfide bonds into proteins for both biopharmaceutical and industrial applications (10,11). However, the sites in proteins that can be cross-linked by a cystine disulfide are typically constrained to a distance between the two β-carbons of ∼5.5 Å (10) and a near 90°dihedral angle for the disulfide bond (12). Thus, the relatively long distances that might be required to bridge distinct protein domains or subunits, or steric constraints at specific sites may preclude the introduction of a natural disulfide bond.…”