ISSN:
0739-4462
Keywords:
apoLp-III
;
amino acid residues
;
lipid binding activity
;
M. sexta
;
Chemistry
;
Food Science, Agricultural, Medicinal and Pharmaceutical Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Biology
Notes:
Chemical modification procedures were employed to neutralize charged amino acid side chains of apolipophorin III (apoLp-III). Glutamate plus aspartate carboxylate side chains were amidated while, in other experiments, the ε-amino groups of lysine residue side chains were acetylated. Circular dichroism (CD) spectroscopy was performed to assess the effect of chemical modification on the secondary structure of apoLp-III. Compared to control, unmodified apoLp-III, both amidated and acetylated apoLp-IIIs possessed significantly diminished levels of α-helical structure. A similarly significant amount of α-helix structure could be induced in both modified apoLp-IIIs, however, by the addition of 50% trifluoroethanol, a helix inducing solvent, indicating that the proteins have retained their capacity to form helical secondary structures. The lipid binding interactions of chemically modified apoLp-IIIs were also examined in lipoprotein binding assays. Whereas control, unmodified apoLp-III displayed lipid binding activity, neither modified apoLp-III was capable of interaction with the substrate lipid surface. In phospholipid binding assays using the model compound, dimyristoylphosphatidylcholine, acetylated apoLp-III failed to interact while amidated apoLp-III showed limited interaction. When sodium dodecyl sulfate (SDS) micelles were employed as a model lipid surface, interaction of the modified apoLp-IIIs was observed. To characterize the relative stability of the interaction of control and modified apoLp-IIIs with SDS micelles, urea denaturation studies were performed. These experiments showed that, while control and amidated apoLp-IIIs were relatively resistant to urea induced denaturation, acetylated apoLp-III was susceptible. Taken as a whole, the results suggest that charged amino acid residues play an important role in stabilization of the lipid-free helix bundle conformation of apoLp-III and may promote stabilization of the lipid bound state through charge-charge interactions with lipoprotein surface components. © 1995 Wiley-Liss, Inc.
Additional Material:
6 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/arch.940300210
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