Turning G Proteins On and Off Using Peptide Ligands

Intracellular Gα subunits represent potential therapeutic targets for a number of diseases. Here we describe three classes of new molecules that modulate G protein signaling by direct targeting of Gα. Using messenger RNA display, we have identified unique peptide sequences that bind Gα_(i1). Functionally, individual peptides were found that either enhance or repress basal levels of G protein-activated inwardly rectifying potassium (GIRK) channel signaling, a downstream effector of G protein activation, indicating that the peptides directly turn G proteins on or off in vivo. A third functional class acts as a signaling attenuator; basal GIRK channel activity is unaffected but responses to repeated G protein activation are reduced. These data demonstrate that G protein-directed ligands can achieve physiological effects similar to those resulting from classical receptor targeting and may serve as leads for developing new classes of therapeutics

The voltage sensitive Lc-type Ca(2+) channel is functionally coupled to the exocytotic machinery

Although N- and P-type Ca(2+) channels predominant in fast-secreting systems, Lc-type Ca(2+) channels (C-class) can play a similar role in certain secretory cells and synapses. For example, in retinal bipolar cells, Ca(2+) entry through the Lc channels triggers ultrafast exocytosis, and in pancreatic β-cells, evoked secretion is highly sensitive to Ca(2+). These findings suggest that a rapidly release pool of vesicles colocalizes with the Ca(2+) channels to allow high Ca(2+) concentration and a tight coupling of the Lc channels at the release site. In binding studies, we show that the Lc channel is physically associated with synaptotagmin (p65) and the soluble N-ethylmaleimide-sensitive attachment proteins receptors: syntaxin and synaptosomal-associated protein of 25 kDa. Soluble N-ethylmaleimide-sensitive attachent proteins receptors coexpressed in Xenopus oocytes along with the Lc channel modify the kinetic properties of the channel. The modulatory action of syntaxin can be overcome by coexpressing p65, where at a certain ratio of p65/syntaxin, the channel regains its unaltered kinetic parameters. The cytosolic region of the channel, Lc(753–893), separating repeats II–III of its α1C subunit, interacts with p65 and “pulls” down native p65 from rat brain membranes. Lc(753–893) injected into single insulin-secreting β-cell, inhibits secretion in response to channel opening, but not in response to photolysis of caged Ca(2+), nor does it affect Ca(2+) current. These results suggest that Lc(753–893) competes with the endogenous channel for the synaptic proteins and disrupts the spatial coupling with the secretory apparatus. The molecular organization of the Lc channel and the secretory machinery into a multiprotein complex (named excitosome) appears to be essential for an effective depolarization evoked exocytosis

Additional file 1: Table S1. of Does the transfer of a poor quality embryo together with a good quality embryo affect the In Vitro Fertilization (IVF) outcome?

Regression model for live birth rate. (DOC 35 kb