The Ant-Pro Reverse-Turn Motif. Structural Features and Conformational Characteristics

• Published in: European journal of organic chemistry Vol. 2013; no. 17; pp. 3529 - 3542
• Main Authors: Thorat, Vijaykumar H., Ingole, Tukaram S., Vijayadas, Kuruppanthara N., Nair, Roshna V., Kale, Sangram S., Ramesh, Veera V. E., Davis, Hilda C., Prabhakaran, Panchami, Gonnade, Rajesh G., Gawade, Rupesh L., Puranik, Vedavati G., Rajamohanan, Pattuparambil R., Sanjayan, Gangadhar J.
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 01-06-2013; WILEY‐VCH Verlag; Wiley Subscription Services, Inc
• Subjects: Amino acids; Bacteriology; Hydrogen bonds; Peptides; Peptidomimetics; Protein folding; Protein structures
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.201201739

This article details the characteristic conformational features of the Ant‐Pro reverse turn ― a folded pseudo β‐turn motif that displays a closed nine‐membered‐ring hydrogen‐bonded network involving just two amino acid residues, namely anthranilic acid (Ant; a constrained β‐amino acid), and proline (Pro; a constrained α‐amino acid). The results from the extensive investigation of ten crystal structures and their NMR conformations in the solution state provide a clear idea about the conformational characteristics of the Ant‐Pro reverse turn. The Ant and Pro residues, which form the turn segment, maintain a perfect antiperiplanar orientation throughout, leaving little possibility for the formation of the otherwise possible six‐membered hydrogen‐bonding that requires a coplanar disposition of the two amino acid residues, as clearly evident from investigation of several crystal structures. The closed hydrogen‐bonded network observed in the Ant‐Pro reverse turn motif, formed in the forward direction of the sequence (1→2 amino acid interactions) involving only two amino acid residues, is in stark contrast to the native β‐turns that involve four residues to form hydrogen‐bonded network featuring backward 1←4 amino acid interactions. The readily available two‐residue Ant‐Pro motif raises the possibility of a practical utility, particularly in the application of rigidifying flexible peptide backbones by inserting the robust Ant‐Pro reverse turn motifs into their backbone.
Characteristic conformational features of the Ant‐Pro reverse turn ― a folded pseudo β‐turn motif with a closed nine‐membered‐ring H‐bonded network involving just two amino acid residues ― are described. The results were obtained from the investigation of ten crystal structures and their NMR conformations in the solution state.