Reverse turn conformation

E. Hisl 11 and Alai 17 Interaction May Enhance Reverse-Turn Conformation... 

Bond, J. P., Deverin, S. P., Inouye, H., el-Agnaf, O. M., Teeter, M. M., and Kirschner, D. A. (2003). Assemblies of Alzheimer s peptides A beta 25—35 and A beta 31-35 Reverse-turn conformation and side-chain interactions revealed by X-ray diffraction./. Struct. Biol. 141, 156-170. 

Figure 1. Schematic representation of a proposed reverse turn conformation of a-MSH at the frog skin receptor. Reproduced with permission from Ref. 50. Copyright 1982, Zoological Society.

Antibodies to the principal neutralizing determinant in the HIV gpl20 V3 loop prevent infection. The -Gly-Pro-Gly-Arg- sequence from residues 312 to 315 is found in 85-90% of HIV isolates and is believed to exist in reverse-turn conformation.1117 To determine the optimum construction of our B-cell epitope, a small library of restricted-turn constructs was screened against the V3 directed MAb 50.1. Based upon our previous analysis, both the B (before binding) and A (after binding) type constructions (Scheme 50) were incorporated into the constrained B-cell epitope library. 

One important insight derived from these structures is that, residues beyond, especially carboxyl terminal to, the core motifs, may also directly contact TRAFS and play an additional energetic and functional role in TRAFS interaction (Fig. 7A, B). In the TRAFS complex with CD40 and LT/3R, the peptides assume a reverse turn conformation that folds back onto the side of the TRAF domain. In the TRAFS complex with TANK the... 

Chauhan and colleagues have studied extensively the impact of incorporation of dehydroamino acids, such as dehydrophenylalanine (APhe), on the backbone conformation ofpeptides (77-80). In general, reverse-turn conformations are preferred in shorter peptides (81, 82) while longer peptides induce 310-helices (83). APhe is planar with no chiral a-carbon and can be incorporated into both right- and left-handed helices. The most favorable conformation of APhe residues are (cp, yc) approximately (-60°, -30°), (-60°, 150°), (80°, 0°), or their mirror images (80). 

Proline has long been known to help a peptide adopt a reverse-turn conformation (71). For example, the classic type VI turn was defined as having a cm-amide bond between residues i + 1 and i + 2, which proline facilitates in the i + 2 position due to its disubstituted amide nitrogen. The sequence d-Pro-l-Pro in particular has been found to adopt a reverse-turn conformation (84-86) and alternating d/l amino acid sequences facilitate cycli-zation of small peptides as discussed in a review of cyclization of peptides and depsipeptides by Davies (87). Particular difficulties in cyclization of linear tetrapeptides containing residues of the same chirality have been found (88). Durani has discussed designing small folded proteins based on an alphabet of d- and L-amino acids (89). 

Two-dimensional representation of the reverse turn conformation of a-MSH. The shaded area represents the messenger sequence or active site. Replacement of MeMand Gly-10 by oxidatively coupled Cys residues results in [CyiVCys °]-a-MSH, a superpotent MSH. 

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