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Conformational and structural analysis of the equilibrium between single- and double-strand beta-helix of a D,L-alternating oligonorleucine.

Abstract：

:Alternating sequences of D and L residues in peptides are directly related to the formation of several kinds of regular helical conformations usually called beta-helices. The major feature of these structures is that they can be associated with the transmembrane ion-conducting channel activity in some natural antibacterial peptides. The study of alternating D,L synthetic peptides is critical to understand how factors such as surrounding media, main chain length, type of side chain and terminal groups, among others, can determine the adoption of a specific kind of beta-helix. Early studies pointed out that the peptides Boc-(D-NLeu-L-NLeu)(6)-D-MeNLe-L-Nl-D-Nl-L-Nl-OMe (Boc: tert-butyloxycarbonyl) and Boc-L-Nle-(D-Nle-L-Nle)(5)-D-MeNle-L-Nle-D-Nle-L-Nle-OMe adopt in chloroform a unique detectable conformation single beta(4.4)- and double beta(5.6) upward arrow downward arrow -helix, respectively. The influence of terminal groups on the final stable conformation of N-formylated peptides has been studied in this work. The initial basic NMR data analysis of a synthetic alternating D,L-oligopeptide with ten norleucines, N-methylated on the residue 7 and having HCO- and -OMe as terminal groups clearly indicates the coexistence of two different conformations in equilibrium. NMR data and molecular dynamics calculations point to a dimeric antiparallel beta-helix structure beta(5.6) upward arrow downward arrow for the main conformation. On the other hand, NMR data suggest a single beta-helix structure beta(4.4) for the second conformation. Finally, a thermodynamic analysis of the equilibrium between both conformations has been carried out by one-dimensional NMR measurements at ten different temperatures. The temperature at which 50% of dimer conformation is dissociated is 319 K. In addition, the dimer-monomer equilibrium curve obtained shows a DeltaG>0 for the whole range of studied temperatures, and its behavior can be considered similar to the thermodynamic denaturation protein processes.

journal_name

Biopolymers

journal_title

Biopolymers

authors

Navarro E,Fenude E,Celda B

doi

10.1002/bip.10549

subject

Has Abstract

pub_date

2004-02-05 00:00:00

pages

229-41

issue

eissn

0006-3525

issn

1097-0282

journal_volume

pub_type

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Conformational and structural analysis of the equilibrium between single- and double-strand beta-helix of a D,L-alternating oligonorleucine.