Article

Peptide adsorption to lipid bilayers: slow processes revealed by linear dichroism spectroscopy.

Department of Chemistry, University Science Laboratories, Durham, DH1 3LE, United Kingdom.
Biophysical Journal (impact factor: 3.65). 03/2009; 96(4):1399-407. DOI:10.1016/j.bpj.2008.10.039
Source: PubMed

ABSTRACT The adsorption and insertion kinetics for the association of two 34-residue cyclic peptides with phosphocholine membranes have been studied using circular and linear dichroism approaches. The two peptides studied are identical with the exception of two residues, which are both tyrosine in one of the peptides and tryptophan in the other. Both peptides adopt random coil conformations in solution in the absence of membranes and do not aggregate at concentrations below 20 microM. After addition to liposome dispersions, circular dichroism spectroscopy indicated that both peptides undergo an extremely rapid transformation to a beta-conformation that remains unchanged throughout the remainder of the experiment. Linear dichroism (LD) spectroscopy was used to study the kinetics of membrane adsorption and insertion. The data were analyzed by nonlinear least squares approaches, leading to identification of a number of bound states and their corresponding LD spectra. Two pseudo-first order processes could be identified that were common to both peptides. The first occurred with a time constant of the order of 1 min and led to a bound state characterized by weak LD signals, with significant bands corresponding to the transitions of aromatic side chains. The second process occurred with an unusually long time constant of between 75 and 100 min, forming a state with considerably stronger positive LD absorbance in the far-ultraviolet region of the spectrum. For the tyrosine-substituted peptide, a third slow process with a long time constant (76 min) could also be delineated and was attributed to rearrangements of the peptide within the membrane.

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Keywords

1 min
 
34-residue cyclic peptides
 
bound state
 
circular dichroism spectroscopy
 
corresponding LD spectra
 
far-ultraviolet region
 
insertion kinetics
 
linear dichroism approaches
 
membrane adsorption
 
phosphocholine membranes
 
pseudo-first order processes
 
random coil conformations
 
rapid transformation
 
remains unchanged
 
second process
 
significant bands corresponding
 
stronger positive LD absorbance
 
third slow process
 
tyrosine-substituted peptide
 
weak LD signals