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Experiments were performed to investigate the synthetic peptides of human apolipoprotein A-I containing tandem amphipathic alpha-helices. Results showed that peptides one to two and nine to ten exhibited significantly higher lipid affinity than other peptides. It was also observed that except for peptides four to five and five to six, all the peptides possess higher lipid affinities compared to constituent helices. However, the lipid affinities of the peptides was neither equal nor higher to the sum of the lipid affinities of the constituent helices.

The N-terminal 43 residues of human apolipoprotein A-I (apo hA-I) are necessary to maintain and stabilize the structure of these amino acids. They also play a crucial role in the conformational switch between the lipid-free and lipid-bound forms. Denaturant-induced unfolding, binding of the fluorescent probe 1-anilinonaphthalene-8-sulfonate, surface balance measurements and far- and near-ultraviolet circular dichroic spectroscopy showed significant structural differences between lipid-free apo (delta)(1-43)A-I and apo hA-I. According to spectral and physical measurements, apo (delta)(1-43)A-I has a folded, tertiary structure, although it is substantially less stable than that of apo hA-I.

Class A exchangeable apolipoproteins and noexchangeable apolipoproteins play vital roles in the transportation of lipid-soluble molecules during lipid metabolism. The A-II, C-I, C-II and C-III apolipoproteins have the highest lipid affinity among exchangeable apolipoproteins due to the presence of amphipathic helices. Class Y helices also exhibit higher lipid affinity compared to class A1 helices. Interfacial lysine residues increase lipid affinity and assist in the anchoring of the amphipathic helix to the lipid bilayer.

An 18-residue peptide (AspTrpLeuLysAlaPheTyrAspLysValAlaGluLysLeu- LysGluAlaPhe), 18A, binds phospholipds due to its class A amphipathic helix and its NMR spectra shows that these helices prefer antiparallel arrangements even if they are not covalently linked. The Lys present in the polar head of the amphipathic helix are noninteracting and are fully hydrated while those in the Ac-18A-NH2 exist in different microenvironments. The location of the Lys residues with respect to the polar-nonpolar interface of the helix determines their titration behaviour. The NMR spectra is discussed.

Magainins lyse only bacterial cells because they contain a Glu residue that interacts with the cholesterol in eukaryotic cells to prevent the formation of a peptide wedge that lyses cell membranes. Experiments with three synthetic class L peptides showed that hemolysis was inhibited by peptides that contained a Glu residue. Many class L venoms are structurally similar to magainins, which are natural antibiotics. But venoms lack the Glu residue and so are able to lyse eukaryotic cells.

The melanocortin-5 receptor (MC5R) is a subtype receptor of the melanocortin receptor (MCR) family, which is expressed centrally, as well as in a variety of peripheral tissues. MC5R has been implicated in many different physiological fields such as lipid metabolism and exocrine function. However, the specific molecular determinants of MC5R responsible for ligand binding and receptor signaling are currently unknown. The aim of this study is to determine the molecular basis of human MC5R (hMC5R) responsible for ligand binding and receptor signaling. Twenty-four single mutations of hMC5R were created and tested. Our results indicate that (l) substituting charged amino acid residue E92 in transmembrane domain 2 (TM2), aspartic acid 115 (D115) and D119 in TM3, and histidine (H) 257 in TM6 with alanine dramatically reduced NDP-α-MSH binding affinity and receptor signaling and (2) substituting aromatic amino acids phenylalanine (F) 195 in TM5, F254 in TM6, and H276 in TM7 with alanine also significantly decreased NDP-α-MSH binding and receptor activity. Combining pharmacological results and computer modeling, our results suggest that D115 and D119 in TM3, F195 in TM5, and F254 in TM6 may form a binding pocket for NDP-α-MSH binding. Our results provide important information about the structural aspects of hMCSR responsible for ligand binding and receptor signaling. [ABSTRACT FROM AUTHOR]

Provides information on a study investigating the synthetic peptides of human apolipoprotein A-I containing tandem amphipathic ...-helixes. Methodology and materials used to conduct the study; Information on the interaction of peptides with phospholipid monolayers; Findings of the study.