Conopressin-T from Conus tulipa Reveals an Antagonist Switch in Vasopressin-like Peptides

Abstract

We report the discovery of conopressin-T, a novel bioactive peptide isolated from Conus tulipa venom. Conopressin-T belongs to the vasopressin-like peptide family and displays high sequence homology to the mammalian hormone oxytocin (OT) and to vasotocin, the endogenous vasopressin analogue found in teleost fish, the cone snail's prey. Conopressin-T was found to act as a selective antagonist at the human V 1a receptor. All peptides in this family contain two conserved amino acids within the exocyclic tripeptide (Pro 7 and Gly 9 ), which are replaced with Leu 7 and Val 9 in conopressin-T. Whereas conopressin-T binds only to OT and V 1a receptors, an L7P analogue had increased affinity for the V 1a receptor and weak V 2 receptor binding. Surprisingly, replacing Gly 9 with Val 9 in OT and vasopressin revealed that this position can function as an agonist/antagonist switch at the V 1a receptor. NMR structures of both conopressin-T and L7P analogue revealed a marked difference in the orientation of the exocyclic tripeptide that may serve as templates for the design of novel ligands with enhanced affinity for the V 1a receptor.The vasopressin (AVP) 3 and oxytocin (OT) peptides were originally discovered and identified as neurohypophysial hormones in mammals (1). In humans, AVP acts via three vasopressin receptors (vascular V 1a R, pituitary V 1b R, and renal V 2 R), whereas OT acts via one OT receptor (OTR). All targets are members of the G protein-coupled receptor family (2). Peripherally, they regulate water balance, the control of blood pressure, and contraction of uterine smooth muscle and mammary myoepithelium (3). Centrally, these peptides affect levels of aggression, depression, and young parent bonding (4 -6). Endogenous analogues of OT and AVP have been reported in nonmammalian vertebrates, annelids, molluscs, and insects, suggesting an old lineage for these peptides (7). Surprisingly, two variants were also found in the venom of predatory cone snails. The original discovery of these two AVP analogues, named conopressins, was based on the characteristic "scratching" effect observed upon intracerebral injection into mice (8). Although the sequences of conopressins are similar to vasopressin itself, they have an additional positive charge in position 4, which is only found in two other endogenous vasopressin analogues, cephalotocin (Octopus vulgaris) and annetocin (Eisenia foetida). Conopressin-S was isolated from Conus striatus, whereas conopressin-G was first isolated from Conus geographus venom but later found in Conus imperialis venom as well as in tissue extracts of the nonvenomous snails Lymnea stagnalis and Aplysia californica and the leech Erpobdella octoculata (9 -11).Molluscs of the genus Conus produce bioactive peptides in a combinatorial fashion. As demonstrated for the snake toxins (12), most conotoxins or conopeptides are believed to be derived from an endogenous structural template (13). Because conopressin-G is widely distributed, it may represent the endogenous hormone in Gastropods and Annelid...

Functional Hypervariability and Gene Diversity of Cardioactive Neuropeptides

“…5). Similar cases have been reported for other related peptides such as conopressins, oxytocin, and vasopressin in which changes in amino acids at position 7, 8, and 9 define their affinity to the oxytocin and vasopressin 1a and 2 type receptors and ultimately their physiological effects (9).…”

Oxytocic plant cyclotides as templates for peptide G protein-coupled receptor ligand design

“…At a more general level, our work provides a proof of concept that naturally occurring peptides serve as templates for GPCR ligand design (25,32). Cyclotides represent a natural combinatorial peptide library, and they probe a chemical space that is difficult to target by using small organic molecules that have been created by various synthetic strategies.…”

Conus Venom Peptide Pharmacology

“…Vasopressin and oxytocin receptors belong to the GPCR family A and apparently bind vasopressins and conopressins in a pocket formed by the arrangement of the seven transmembrane domains (Mouillac et al, 1995;Dutertre et al, 2008). On the basis of extracellular domain exchanges between and oxytocin receptor, it has been proposed that the three extracellular loops are also important for agonist binding (Postina et al, 1996).…”

“…Therefore, conopressin-G was proposed to represent the endogenous vasopressin homolog in these invertebrates. However, novel conopressins have since been discovered from other cone snail species, supporting a role in envenomation (Möller and Marí, 2007;Dutertre et al, 2008;Ueberheide et al, 2009). We were surprised that conopressin-T acted as a V 1 -vasopressin receptor-selective antagonist, with partial agonist activity at the oxytocin receptor and replacing Gly9 with Val9 also switched the activity of vasopressin and oxytocin from agonist to antagonist .…”