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Reverse Turns (reverse + turn)

Distribution by Scientific Domains

Chemistry	75%

Selected Abstracts

Folding Control in Cyclic Peptides through N-Methylation Pattern Selection: Formation of Antiparallel ,-Sheet Dimers, Double Reverse Turns and Supramolecular Helices by 3,,, Cyclic Peptides

CHEMISTRY - A EUROPEAN JOURNAL, Issue 7 2008
Manuel Amorín Dr.
Abstract Peptide foldamers constitute a growing class of nanomaterials with potential applications in a wide variety of chemical, medical and technological fields. Here we describe the preparation and structural characteristics of a new class of cyclic peptide foldamers (3,,,-CPs) that, depending on their backbone N-methylation patterns and the medium, can either remain as flat rings that dimerize through arrays of hydrogen bonds of antiparallel ,-sheet type, or can fold into twisted double reverse turns that, in the case of double ,-turns, associate in nonpolar solvents to form helical supramolecular structures. A 3,,,-CP consists of a number of multiples of a repeat unit made up of four amino acid residues of alternating chirality: three corresponding to ,-amino acids and one to a ,-amino acid (a cis -3-aminocycloalkanecarboxylic acid). [source]

Engineering Metal Complexes of Chiral Pentaazacrowns as Privileged Reverse-turn Scaffolds

CHEMICAL BIOLOGY & DRUG DESIGN, Issue 2 2007
Ye Che
Reverse turns are common structural motifs and recognition sites in protein/protein interactions. The design of peptidomimetics is often based on replacing the amide backbone of peptides by a non-peptidic scaffold while retaining the biologic mode of action. This study evaluates the potential of metal complexes of chiral pentaazacrowns conceptually derived by reduction of cyclic pentapeptides as reverse-turn mimetics. The possible conformations of metal complexes of chiral pentaazacrown scaffolds have been probed by analysis of 28 crystal structures complexed with six different metals (Mn, Fe, Co, Ni, Cu, and Zn). The solvated structures as well as the impact of complexation with different metals/oxidation states have been examined with density functional theory (DFT) calculation as explicitly represented by interactions with a single water molecule. The results suggest that most reverse-turn motifs seen in proteins could be mimicked effectively with a subset of metal complexes of chiral pentaazacrown scaffolds with an RMSD of approximately 0.3 Å. Due to the relatively fixed orientation of the pendant chiral side groups in these metal complexes, one can potentially elicit information about the receptor-bound conformation of the parent peptide from their binding affinities. The presence of 20 H-atoms on the pentaazacrown ring that could be functionalized as well as the conformational perturbations available from complexation with different metals offer a desirable diversity to probe receptors for reverse-turn recognition. [source]

Physical-chemical determinants of turn conformations in globular proteins

PROTEIN SCIENCE, Issue 8 2007
Timothy O. Street
Abstract Globular proteins are assemblies of ,-helices and ,-strands, interconnected by reverse turns and longer loops. Most short turns can be classified readily into a limited repertoire of discrete backbone conformations, but the physical,chemical determinants of these distinct conformational basins remain an open question. We investigated this question by exhaustive analysis of all backbone conformations accessible to short chain segments bracketed by either an ,-helix or a ,-strand (i.e., ,-segment-,, ,-segment-,, ,-segment-,, and ,-segment-,) in a nine-state model. We find that each of these four secondary structure environments imposes its own unique steric and hydrogen-bonding constraints on the intervening segment, resulting in a limited repertoire of conformations. In greater detail, an exhaustive set of conformations was generated for short backbone segments having reverse-turn chain topology and bracketed between elements of secondary structure. This set was filtered, and only clash-free, hydrogen-bond,satisfied conformers having reverse-turn topology were retained. The filtered set includes authentic turn conformations, observed in proteins of known structure, but little else. In particular, over 99% of the alternative conformations failed to satisfy at least one criterion and were excluded from the filtered set. Furthermore, almost all of the remaining alternative conformations have close tolerances that would be too tight to accommodate side chains longer than a single ,-carbon. These results provide a molecular explanation for the observation that reverse turns between elements of regular secondary can be classified into a small number of discrete conformations. [source]

Folding Control in Cyclic Peptides through N-Methylation Pattern Selection: Formation of Antiparallel ,-Sheet Dimers, Double Reverse Turns and Supramolecular Helices by 3,,, Cyclic Peptides