Block poly(Ala)-poly(Lys). A water-soluble model for intrinsic membrane proteins?

Solubilization of hydrophobic peptides by reversible cysteine PEGylation

"PEG-a-Cys" reagent, synthesized by the esterification of monomethoxy-poly(ethylene glycol) (avg. MW = 5 kDa) to Ellman's reagent [5,5'-dithiobis(2-nitrobenzoic acid)], is shown to "PEGylate" reversibly the cysteine residue of a 25-residue synthetic hydrophobic peptide (H2N-REAAALAAAAALAAWAALCPARRRR-CO2H) designed to model a transmembrane segment of a membrane protein. A mixed disulfide bond was formed between the reagent and the peptide that was readily cleaved with the mild reducing agent tricarboxyethylphosphine hydrochloride (TCEP.HCl). Carboxypeptidase B digestion of the charged carboxyl terminus of the peptide through to the Ala residue--which mimics the enzymatic cleavage of a TM segment from a fusion protein--releases a highly hydrophobic peptide. A time-dependent decrease in the amplitude of the digested peptide circular dichroism (CD) spectra was attributed to the aggregation and/or precipitation of the peptide. While PEGylation of the peptide with PEG-a-Cys had a negligible effect on conformation, it inhibited the loss of CD amplitude in both intact and digested peptides, suggesting that it was effective in solubilization of hydrophobic peptides.

Investigation on the interactions of peptides in the assembly of liposome and peptide by fluorescence

The peptide-lipid and the peptide-peptide interactions of hydrophobic linear dipeptides containing tryptophan in liposome were investigated by fluorescence. The linear dipeptides were buried into the hydrophobic region of liposome to induce blue-shift of the fluorescence. With the addition of various anthracene derivatives to liposome, the energy transfer from tryptophan to anthryl group took place, which increased as the temperature decreased below the phase-transition temperature of the membrane. This phenomenon was explained in terms of the phase separation of the membrane, in which crystalline regions without the probes and the domains containing high concentrations of probes are intermixed. The energy-transfer efficiency was larger in the case of peptide acceptors than lipid acceptors. This suggests the presence of special interactions between donor peptide and acceptor peptide.