N-terminal truncated analogs of men 10376 as tachykinin NK-2 receptor antagonists.

Three N-terminal fragments of the selective tachykinin NK-2 receptor antagonist MEN 10376 (H-Asp-Tyr-DTrp-Val-DTrp-DTrp-Lys-NH2) have been synthesized and tested in several mammalian tissues in order to establish the minimum length of the peptide chain for maintenance of the antagonist activity. Biological activity has been determined on the rabbit pulmonary artery (RPA) and hamster trachea (HT) preparations, chosen as representative of the NK-2A and NK-2B receptor subtypes, respectively, and on the rabbit bronchus (RB), guinea-pig bronchus (GPB), human urinary bladder (HuUB), human ileum (HuI) and human colon (HuC) preparations to verify the previously described NK-2A character of these tissues. The N-terminal tetrapeptide was inactive in the RPA and HT, while the N-terminal hexa- and penta- peptides maintained antagonist activity in all preparation investigated. The selectivity of the latter two peptides confirms that the receptor expressed in RB, GPB, HuUB, HuC and HuI tissues is of the NK-2A type.     

Loop 2 of limulus myosin III is phosphorylated by protein kinase A and autophosphorylation

Little is known about the functions of class III unconventional myosins although, with an N-terminal kinase domain, they are potentially both signaling and motor proteins. Limulus myosin III is particularly interesting because it is a phosphoprotein abundant in photoreceptors that becomes more heavily phosphorylated at night by protein kinase A. This enhanced nighttime phosphorylation occurs in response to signals from an endogenous circadian clock and correlates with dramatic changes in photoreceptor structure and function. We seek to understand the role of Limulus myosin III and its phosphorylation in photoreceptors. Here we determined the sites that become phosphorylated in Limulus myosin III and investigated its kinase, actin binding, and myosin ATPase activities. We show that Limulus myosin III exhibits kinase activity and that a major site for both protein kinase A and autophosphorylation is located within loop 2 of the myosin domain, an important actin binding region. We also identify the phosphorylation of an additional protein kinase A and autophosphorylation site near loop 2, and a predicted phosphorylation site within loop 2. We show that the kinase domain of Limulus myosin III shares some pharmacological properties with protein kinase A, and that it is a potential opsin kinase. Finally, we demonstrate that Limulus myosin III binds actin but lacks ATPase activity. We conclude that Limulus myosin III is an actin-binding and signaling protein and speculate that interactions between actin and Limulus myosin III are regulated by both second messenger mediated phosphorylation and autophosphorylation of its myosin domain within and near loop 2.     

R7BP, a novel neuronal protein interacting with RGS proteins of the R7 family

The R7 subfamily of the regulators of G protein signaling (RGS) proteins is represented by four members broadly expressed in the mammalian nervous system. Here we report that in the brain all four R7 proteins form tight complexes with a previously unidentified protein, which we call the R7-binding protein or R7BP. We initially identified R7BP as a protein co-precipitating with the R7 protein, RGS9, from extracts obtained from the striatal region of the brain. We further showed that R7BP forms a tight complex with RGS9 in vitro and that this binding occurs via the N-terminal DEP domain of RGS9. R7BP is expressed throughout the entire central nervous system but not in any of the tested non-neuronal tissues. All four R7 RGS proteins co-precipitate with R7BP from brain extracts and recombinant R7 proteins bind recombinant R7BP with high efficiency. The closest homolog of R7BP is R9AP which was previously found to interact with RGS9 in photoreceptors. Both R7BP and R9AP are related to the syntaxin subfamily of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins involved in vesicular trafficking and exocytosis. In photoreceptors R9AP regulates several critical properties of RGS9 including its intracellular targeting, stability and catalytic activity. This suggests that R7BP interactions with R7 proteins in the brain may also bear major functional significance.