RRP17 (red) binds CAPS1 (green) to help the heart pump out hormones.
Rybkin et al. deal with matters of the heart. In a search for novel heart-specific signaling proteins that might regulate functions such as heart rate, they previously found one that was similar to the signal-transducing small G-protein, Ras. They called the newbie RRP17, for Ras-related protein on human chromosome 17.
RRP17 binds to a protein called CAPS1, which enhances neurotransmitter vesicle release. The team now shows that CAPS1 levels rise in heart cells in response to cardiac stress. RRP17 levels did not increase during the stress, but what was already there promoted CAPS1 to drive the release of secretory vesicles containing a blood pressure–reducing hormone.
Mice lacking RRP17 secreted less of the hormone and consequently had higher blood pressure. Although RRP17, like CAPS1, was also abundant in the brain, the team has yet to observe any neurological impairment in the mice lacking the protein. Although the mice function just fine in their cage, explain the authors, whether they would perform normally in cognitive tests remains to be determined. 
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