Amphipathic polyproline peptides stimulate cholesterol efflux by the ABCA1 transporter

Abstract

ApoA-I mimetics are short synthetic peptides that contain an amphipathic αα-helix and stimulate cholesterol efflux by the ABCA1 transporter in a detergent-like extraction mechanism. We investigated the use of amphipathic peptides with a polypro helix for stimulating cholesterol efflux by ABCA1. Polypro peptides were synthesized with modified prolines, containing either a hydrophobic phenol group (Prop) or a polar N-acetylgalactosamine (Prog) attached to the pyrrolidine ring and were designated as either PP-2, 3, 4, or 5, depending on the number of 3 amino acid repeat units (Prop - Prog - Prop). Based on molecular modeling, these peptides were predicted to be relatively rigid and to bind to a phospholipid bilayer. By CD spectroscopy, PP peptides formed a Type-II polypro helix in an aqueous solution. PP-2 was inactive in promoting cholesterol efflux, but peptides with more than 2 repeat units were active. PP-4 showed a similar Vmax as a much longer amphipathic α-αhelical peptide, containing 37 amino acids, but had a Km that was approximately 20-fold lower. PP peptides were specific in that they did not stimulate cholesterol efflux from cells not expressing ABCA1 and were also non-cytotoxic. Addition of PP-3, 4 and 5 to serum promoted the formation of smaller size HDL species (7 nM) and increased its capacity for ABCA1-dependent cholesterol efflux by approximately 20-35% (p<0.05). Because of their relatively small size and increased potency, amphipathic peptides with a polypro helix may represent an alternative structural motif for the development of apoA-I mimetic peptides.

Structural properties of apolipoprotein A-I mimetic peptides that promote ABCA1-dependent cholesterol efflux

“…As Fig. 5a shows, both hyd and neu are effective in promoting cholesterol efflux and their apparent Vmax of 35–40%/18 h is similar to previously described apoA-I mimetic peptides 30 , 37 , 40 . Neu, however, is slightly less potent than hyd and at higher concentrations the rate of efflux appears to decrease, which has been previously described for other apoA-I mimetic peptides possibly due to either cytotoxicity or peptide aggregation 36 .…”

“…Hyd was the most helical peptide in both solvents. A potential explanation for these findings is that the peptides form oligomers in the aqueous buffer by the association of their hydrophobic faces similar to other apoA-I mimetic peptides 36 , 37 . This hypothesis was tested by cross-linking free peptides when dissolved in aqueous buffer.…”

Apolipoprotein Mimetic Peptides: Potential New Therapies for Cardiovascular Diseases

“…These structural changes also make these peptides resistant to proteolysis [ 49 , 50 ]. Other newer apoA-I mimetics use a different backbone, such as polyproline [ 51 ], which forms a very stable left-handed helix [ 52 ]. To the proline ring, hydrophobic and polar groups were attached so that it forms an amphipathic helix and short polypro peptides containing as few as nine residues were shown to be effective for removing cholesterol from cells by the ABCA1 transporter [ 51 ].…”

“…Other newer apoA-I mimetics use a different backbone, such as polyproline [ 51 ], which forms a very stable left-handed helix [ 52 ]. To the proline ring, hydrophobic and polar groups were attached so that it forms an amphipathic helix and short polypro peptides containing as few as nine residues were shown to be effective for removing cholesterol from cells by the ABCA1 transporter [ 51 ]. Short self-assembling cyclic d,l-α-peptides have also been described to promote cellular cholesterol efflux from cells and to increase plasma levels of pre-β HDL in animal models [ 53 ].…”

ATP‑binding cassette transporter A1: A promising therapy target for prostate cancer (Review)

“…This may be explained by the use of lipid as an energy source during growth and metastasis of prostate cancer cells. ABCA1 has been shown to play a critical role in the synthesis of HDL particles by exporting cellular cholesterol (19,20). Considering these findings, further investigation into ABCA1 as a tumor suppressor in prostate cancer is required.…”