Short alanine-based peptides may form 310-helices and not α-helices in aqueous solution

A Microscopic View of Helix Propagation: N and C-terminal Helix Growth in Alanine Helices

“…Millhauser (1995) suggests that, because helix formation may not be driven to completion in short peptides, short pieces of 3 10 -helix should be found at the end of a-helices. This proposal is consistent with the ESR studies of his group (Fiori et al, 1993;Miick et al, 1992Miick et al, , 1993, and with the experimental and theoretical (Nemethy et al, 1967) work of others.…”

“…Recent experimental work (Fiori et al, 1993;Miick et al, 1992Miick et al, , 1993 has suggested that polyalanine helices may form 3 10 -helices rather then a-helices, especially at the ends. Both the 3 10 -helix and the a-helix occupy approximately the same region of conformational space.…”

“…Thus, the combined composition has often been labelled as helical. In an effort to distinguish between these two helical types, Millhauser and co-workers (Fiori et al, 1993;Miick et al, 1992Miick et al, , 1993 used double label electron spin resonance (ESR) spectroscopy to study peptide sequences similar to the synthetic helices previously studied by Baldwin and co-workers (Marqusee et al, 1989). Based on an analysis of the distances between spin labels, they concluded that there were significant regions of 3 10 -helix at the ends of helices that had previously been thought to be entirely a-helical.…”

The thermal unfolding of the ribosome-inactivating protein saporin-S6 characterized by infrared spectroscopy

“…The assignment of the band at 1671 cm − 1 is less certain but it can be related to highfrequency β-sheet indicating its antiparallel orientation [43,44] with the contribution of β-turns. Finally, the contribution of the three 3 10 -helices could be displayed by the band at 1646 cm −1 [45] where also unordered structures absorb, and it is also expected to overlap the band at 1662 cm − 1 [46,47]. The peaks below 1620 cm − 1 are due to the amino acid side chain absorption [48] except for the band close to 1550 cm −1 that is due to the residual amide II band, i.e.…”

Characterization of Alanine-Rich Peptides, Ac-(AAKAA)n-GY-NH2(n= 1−4), Using Vibrational Circular Dichroism and Fourier Transform Infrared. Conformational Determination and Thermal Unfolding

“…While considerable data have arisen with regard to various factors that stabilize such helical formation in water, including length effects (Scholtz et al, 1991a;Rohl et al, 1992), it remained clear that these peptides were exceptionally stable, particularly with respect to the helix stability predictions of Zimm-Bragg theory using parameters determined from "host-guest" experiments (Scholtz et al, 1992;Zimm & Bragg, 1959). More recently, the field was given a new twist in a series of papers from Millhauser and co-workers (Hanson et al, 1996a,b;Millhauser, 1995;Fiori et al, 1993;Miick et al, 1991Miick et al, , 1992Miick et al, , 1995 which provided evidence of the possibility of some of these peptides being at least partially in a 3 10 -helical conformation, particularly the shorter ones (Millhauser, 1995;Miick et al, 1992Miick et al, , 1995. Additionally, even longer peptides were proposed to undergo an R-helix to 3 10 -helix transformation as they were heated before eventually assuming a high-temperature coil form (Millhauser, 1995;Miick et al, 1995).…”