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Optimization of Synthetic Proteins: Identification of Interpositional Dependencies Indicating Structurally and/or Functionally Linked Residues
Published on: July 14, 2015
Aib residues in peptaibiotics and synthetic sequences: analysis of nonhelical conformations
Subrayashastry Aravinda1, Narayanaswamy Shamala, Padmanabhan Balaram
1Department of Physics, Indian Institute of Science, Bangalore 560012, India.
Abstract:
The alpha-aminoisobutyric (Aib) residue has generally been considered to be a strongly helicogenic residue as evidenced by its ability to promote helical folding in synthetic and natural sequences. Crystal structures of several peptide natural products, peptaibols, have revealed predominantly helical conformations, despite the presence of multiple helix-breaking Pro or Hyp residues. Survey of synthetic Aib-containing peptides shows a preponderance of 3(10)-, alpha-, and mixed 3(10)/alpha-helical structures. This review highlights the examples of Aib residues observed in nonhelical conformations, which fall 'primarily' into the polyproline II (P(II)) and fully extended regions of conformational space. The achiral Aib residue can adopt both left (alpha(L))- and right (alpha(R))-handed helical conformations. In sequences containing chiral amino acids, helix termination can occur by means of chiral reversal at an Aib residue, resulting in formation of a Schellman motif. Examples of Aib residues in unusual conformations are illustrated by surveying a database of Aib-containing crystal structures.
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