Functional Hypervariability and Gene Diversity of Cardioactive Neuropeptides

Abstract

Crustacean cardioactive peptide (CCAP) and related peptides are multifunctional regulatory neurohormones found in invertebrates. We isolated a CCAP-related peptide (conoCAP-a, for cone snail CardioActive Peptide) and cloned the cDNA of its precursor from venom of Conus villepinii. The precursor of conoCAP-a encodes for two additional CCAP-like peptides: conoCAP-b and conoCAP-c. This multi-peptide precursor organization is analogous to recently predicted molluscan CCAP-like preprohormones, and suggests a mechanism for the generation of biological diversification without gene amplification. While arthropod CCAP is a cardio-accelerator, we found that conoCAP-a decreases the heart frequency in Drosophila larvae, demonstrating that conoCAP-a and CCAP have opposite effects. Intravenous injection of conoCAP-a in rats caused decreased heart frequency and blood pressure in contrast to the injection of CCAP, which did not elicit any cardiac effect. Perfusion of rat ventricular cardiac myocytes with conoCAP-a decreased systolic calcium, indicating that conoCAP-a cardiac negative inotropic effects might be mediated via impairment of intracellular calcium trafficking. The contrasting cardiac effects of conoCAP-a and CCAP indicate that molluscan CCAP-like peptides have functions that differ from those of their arthropod counterparts. Molluscan CCAP-like peptides sequences, while homologous, differ between taxa and have unique sequences within a species. This relates to the functional hypervariability of these peptides as structure activity relationship studies demonstrate that single amino acids variations strongly affect cardiac activity. The discovery of conoCAPs in cone snail venom emphasizes the significance of their gene plasticity to have mutations as an adaptive evolution in terms of structure, cellular site of expression, and physiological functions.

In the picture: disulfide-poor conopeptides, a class of pharmacologically interesting compounds

“…ConoCAPs or cardioactive peptides from cone snails are described by Möller et al [26]. The conoCAPs (a, b, c, Table 3) reported in this work have up to 78 % of sequence homology with crustacean cardioactive peptides (CCAP, amino acid sequence PFCNAFTGC * ).…”

“…The reduction in HR was lost when the Cys residues were substituted by Ala or when they were S-methylated. On the other hand, less significant changes were observed when intracystine amino acids were replaced by Ala [26]. …”

Molecular Phylogeny, Classification and Evolution of Conopeptides

“…1 as the B and C superfamilies, respectively (the C superfamily has been previously defined by Jimenez et al (2007)); two conoCAP sequences (FN868446.1 and FN868447.1-named X1 in the Fig. 1 and appendix 1) described by Möller et al (2010); and sequences putatively annotated (FJ237364.1, named X2) or without annotation in GenBank (DQ359922.1, EF493183.1/EF493184.1 and DQ359921.1, named respectively X3, X4, and X5). In the Clustal alignment, two other groups of sequences, FJ375238.1/FJ375239.1/FJ375240.1 and EF208033.1 clustered in the superfamily A and O1, respectively with long branches, but corresponded to the independent lineages in the Muscle alignment (X6 and X7, respectively).…”

Conotoxin Gene Superfamilies

“…ConoCAP-a, a short peptide with a single disulphide, was isolated from the venom of Conus villipenii [ 158 ]. It displayed 78% sequence identity to the crustacean cardioactive peptide (CCAP), a multifunctional neurohormone found in invertebrates and nanomolar ligand of a GPCR in D rosophila .…”