Controls exerted by the Aib residue: Helix formation and helix reversal

• Published in: Biopolymers 2001, Vol.60 (5), p.351-365
• Main Author: Karle, Isabella L.
• Format: Article
• Language: English
• Subjects: 6 → 1 type hydrogen bonds; Amino Acid Motifs; Aminocaproates - chemistry; Aminoisobutyric Acids - chemistry; crystal structure analyses; helix perturbations; Hydrogen Bonding; Models, Molecular; Protein Conformation; Protein Structure, Secondary; reversals in ambidextrous helices; solvated helix reversals
• ISSN: 0006-3525; 1097-0282
• DOI: 10.1002/1097-0282(2001)60:5<351::AID-BIP10174>3.0.CO;2-U

The helix forming properties of the achiral α‐amino isobutyric residue (Aib) have been demonstrated by numerous crystal structure analyses of designed and naturally occurring peptides containing one or more Aib residues in the sequence. Experimental and computational results concerning the type of helix obtained, whether the 310‐helix with 4 → 1 type hydrogen bonds or the α‐helix with 5 → 1 hydrogen bonds or mixtures of the two, have been published. This paper deals with residues that, if inserted into a sequence, could perturb the helix‐forming propensity afforded by the presence of Aib residues. Examples of structures will be presented in which Pro, Hyp, Gly–Gly, d‐Ala–Gly, and Lac have been centrally placed in the sequence. In addition to the formation of helices, detailed experimentally obtained conformation information is presented for the role of the Aib residue in reversing the sense of the helix (the Schellman motif) with the consequent formation of the 6 → 1 type hydrogen bond or a solvated 6 → 1 hydrogen bond. Data are presented for 13 molecules with helix reversals at the C‐terminus or near the center of the sequence. Published 2002 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 60: 351–365, 2001