SYNTHETIC PEPTIDES CORRESPONDING TO THE CALMODULIN-BINDING DOMAINS OFSKELETAL-MUSCLE MYOSIN LIGHT-CHAIN KINASE AND HUMAN ERYTHROCYTE CA2-MEMBRANES( PUMP INTERACT WITH AND PERMEABILIZE LIPOSOMES AND CELL)

Synthetic calmodulin-binding (CaM-binding) peptides (CBPs) representin g CaM-binding domains of Ca2+/CaM-dependent enzymes have been reported to interfere with the activity of the melanocyte-stimulating hormone (MSH) receptor function in melanoma cells [Gerst, J. E., & Salomon, Y. (1988) J. Biol. Chem. 263, 7073-7078]. We postulated that membrane li pids may play an important role in the mode of action of CBPs on cells . We therefore tested the ability of CBPs to interact with membrane bi layers. Using artificial phospholipid vesicles, or M2R melanoma cells and cell membranes derived therefrom, as models, we report here that s ynthetic peptides representing the CaM-binding domains of skeletal mus cle myosin light chain kinase (M5) and the human erythrocyte calcium p ump (C28W), as well as other CBPs, interact with lipid bilayers and ce ll membranes. Significant interactions of CBPs with the lipid bilayer were detected in both model systems. M5 and C28W were found to partiti on into the lipid bilayer of melanoma cell membranes and soybean lecit hin vesicles, and surface partition constants obtained (for the liposo me model) were in the range 10(3)-10(4) M-1. In addition, C28W and its N-modified NBD derivative were found to inhibit [I-125]iodo-[Nle4,D-P he7]alphaMSH binding to cultured M2R melanoma cells. These and other C BPs were also found to induce the release of cations and calcein from liposomes, suggesting that the interaction of CBPs with the lipid bila yer increases membrane permeability. Nonrelevant peptides used as cont rols were found ineffective. Melittin, a bee venom derived CBP, and pa rdaxin, a shark-repellent neurotoxin, both membrane-permeating peptide s, were in comparison more potent than the enzyme-derived CBPs that we re not lytic when applied to cells. It is proposed that the tested CBP s act as permeators that partition into the lipid bilayer of the cell membrane, thereby also promoting their interaction with hydrophobic do mains of membrane proteins such as the MSH receptor, consequently elic iting the observed cellular responses.