Calmodulin is a potent target for new hypothalamic neuropeptides

Structure of hypothalamic coronaro-constrictory peptide factors

The following peptide structure in 3 of 5 coronaro-constrictory peptide factors isolated from bovine hypothalamus was determined by amino acid analysis and Edman degradation: 1) (P1)--Val-Val-Tyr-Pro-Trp; 2) (P2)--Val-Val-Tyr-Pro-Trp-Thr; 3) (P3)--Leu-Val-Val-Tyr-Pro-Trp-Thr. A computer search for these amino acid sequences revealed that these peptides represent fragments 33-37; 33-38; 32-38 of the beta-chain of bovine hemoglobin. Solid phase peptide synthesis of 2 peptides (P2 and P3) was carried out. It was established that synthetic peptides had the properties of coronaro-constrictory peptides. The possibility of the formation of hypothalamic coronaro-constrictory peptides in vivo is discussed.

Effects of calmodulin antagonists on antibody binding to calmodulin. Distinct conformers of calmodulin induced by the binding of drugs

An indirect enzyme-linked immunosorbent assay has been used to study the interactions between calmodulin and two calmodulin antagonists, trifluoperazine and a neuropeptide isolated from the hypothalamus. The binding of a monospecific anti-calmodulin antibody, raised in rabbit against dinitrophenylated calmodulin, to calmodulin was tested at various concentrations of these drugs under equilibrium conditions. Trifluoperazine at low concentrations stimulated, but at relatively high concentrations inhibited, immunocomplex formation. The neuropeptide displaced the antibody from calmodulin at nanomolar concentrations. Enzyme-linked immunosorbent assays were also carried out with the large tryptic fragments of calmodulin. The results suggest that (i) the C-terminal fragment binds the antibody with an affinity which is comparable with that of intact calmodulin; (ii) the neuropeptide can form complexes with both N- and C-terminal fragments, but with two orders of magnitude less activity in case of the C-terminal fragment; and (iii) trifluorperazine does not stimulate antibody binding to the C-terminal fragment. Therefore the tertiary structure of calmodulin must be intact to ensure long-distance interactions between the binding sites of trifluoperazine, the neuropeptide and the antibody. These interactions may produce distinct conformers of calmodulin which may exhibit altered potency, not only for antibody binding but also for stimulation/inhibition of target enzymes.

Quantitative evaluation of indirect ELISA. Effect of calmodulin antagonists on antibody binding to calmodulin

A simple linearization procedure has been developed to determine the apparent dissociation constant of the interaction between antigen and antibody from the data of indirect, non-competitive enzyme-linked immunosorbent assays (ELISA). Applying this dissociation constant the binding constant of ligands to antigen can be determined and the quantitative evaluation of the competitive ELISA experiments makes it possible to analyse the affinity of antibody to antigen on the surface and in solution. The binding of the monospecific anti-calmodulin antibody to calmodulin and to solid-phase bound calmodulin has been tested by non-competitive and competitive assays. We have developed an experimental system where binding of the antibody to the solid-phase bound calmodulin has been studied under equilibrium conditions. Competitive ELISA experiments showed that the affinity of antibody to calmodulin on the surface and in solution was almost the same. The binding constant of a hypothalamic neuropeptide to calmodulin was determined using the quantitative ELISA approach. The neuropeptide was found to be of very high inhibitory potency (Kd = 2 nM) and competed with the antibody for calmodulin binding. This simple and sensitive procedure is suitable for screening molecules with anti-calmodulin activity and comparing their efficacy.