ИСТИНА

Cholesterol is an integral component of an animal cell plasma membrane required for its normal functioning. Some pathogenic bacteria and viruses employ cholesterol dependent mechanisms for cell invasion. One of the hypothesis explaining protein cholesterol interactions suggests the existence of the Cholesterol Recognition Amino acid Consensus (CRAC) motifs characterized by a certain amino acid sequence with a polar, aromatic, and positively charged side groups. One of the ways to verify the significance of CRAC motifs in membrane proteins for cholesterol-dependent cell functions is to analyze the impact of CRACcontaining peptides on cholesterol dependent processes. In this context we studied the effects of synthetic peptides derived from influenza virus A protein M1, which contains several α-helices exposing CRAC motifs, on cholesterol-dependent interaction of cultured macrophages IC-21 with test 2-micron particles. Of four CRAC-containing peptides studied, peptide RTKLWEMLVELGNMDKAVKLWRKLKR (P4) containing two CRAC motifs was most efficient; in a micromolar concentration range it dose-dependently modulated the activity of macrophages and at 20–50 μM produced a cytotoxic effect. Extraction of membrane cholesterol by methyl-β-cyclodextrin lowered the toxic concentration of P4. Peptide obtained by substitution by serine of all CRAC-forming amino acids in P4 did not produce any effect at 0.5–50 μM. Neither was effective peptide with substituted aromatic amino acids in CRAC motifs. Peptide STKLWEMLVELGNMDKAVKLWRKLSR with substitution of cationic amino acids in the CRAC was as efficient as P4. Peptide EWGMAVLWERNRKLKKDLKVLKMLRT composed of the same amino acids as P4 but in a random order (“scramble”) and possessing one CRAC motif was not toxic at 50 μM. Our results suggest an important role of CRAC motifs in the mechanisms of the peptide induced modulations of cholesterol dependent cell functions. Possibly viral proteins affect host cell functions in a similar way. CRAC peptides may provide new tools for regulation the activity of cholesterol-dependent proteins and for the design of antimicrobial and immunomodulating drugs.