DISSOCIATION ACTION OF CATIONIC PEPTIDES WITH HYDROPHOBIC RADICALS ON FUNCTIONAL COUPLING
BETWEEN SERPENTINE TYPE RECEPTORS AND GTP-BINDING PROTEINS
A. O. Shpakov 1, I. A. Gurjanov 2, V. I. Vorobjev 3,
E. V. Avdeeva 3, L. A. Kuznetsova 1, S. A. Plesneva 1, N. M. Chubey 1 M. N. Pertseva 1, G. P. Vlasov 2
1 I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry RAS, 2
Institute of Macromolecular Compounds RAS, and 3 Institute of Cytology RAS, St. Petersburg, Russia;
e-mail: shpakov@hormone.ief.spb.su
The coupling of hormone-activated receptor and heterotrimeric G protein is an important step of the signal transduction
through adenylyl cyclase signal system (ACS). The numerous literature data and own results show that G protein-interacting regions,
that are localized in cytoplasmic loops of receptors, have considerable positive charge, can form amphiphilic a-helices and are tightly
associated with the membrane. We studied the influence of model cationic peptides on both basal and stimulated by hormones and
nonhormonal agents adenylyl cyclase (AC) activity and on GTP binding activity of heterotrimeric G proteins in skeletal muscles of rats and
smooth muscles of mollusc Anodonta cygnea. Peptides with hydrophobic radicals of caprinoyl acid (C10):
Lys(C10)-His-Glu-Lys-Lys-(C10)-His-Glu-Lys-Lys(C10)-His-Glu-Lys-Lys(C10)-His-Glu-Lys-Ala-amide (peptide I),
Cys-Lys(C10)-X-Tyr-Lys-Ala-Lys7-Trp-Lys-amide (II),
Cys-X-Trp-Lys-Lys(C10)-Lys2-Lys(C10)-Lys3-Lys(Ñ10)-Òóã-Lys-Lys(Ñ10)-Lys-Lys-amide (III),
where X - ε-aminocaproyl acid residue, were synthesized by solid-phase methodology. IC50 values for inhibiting the
influence of peptides on serotonin- (molluscs) and isoproterenol-stimulated (rats) AC activity were: for peptide I - 56 and 70 mkM, for
peptide II - 32 and 47 mkM, for peptide III - 22 and 28 mkM, respectively. At the same time the peptides weakly decreased AC activity
stimulated by nonhormonal agents (NaF, Gpp[NH]p, forskolin). Peptides I-III stimulated basal activity of the enzyme in both investigated
tissues. The maximum stimulating effects (28-52 %) of the peptides were observed at their concentration 10 mkM. Peptides (10-100 mkM)
increased Gpp[NH]p binding in plasma membranes of mollusc and rat muscles and strongly decreased the influence of the hormones
on the binding. Based on the obtained data we supposed that cationic peptides with hydrophobic radicals mimic G protein-binding regions
of the receptors and can be involved in the regulation of functional coupling between the receptors and G proteins.
Key words: adenylyl cyclase, heterotrimeric G protein, GTP-binding, guanine nucleotides, isoproterenol, mollusc
Anodonta cygnea, serotonin, cationic peptide
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