9.A.14.13.16
The P2Y purinoreceptor 2, P2Y2 of 377 aas and 7 TMSs.  Receptor for ATP and UTP coupled to G-proteins that activate a phosphatidylinositol-calcium second messenger system. The affinity range is UTP = ATP > ATP-gamma-S >> 2-methylthio-ATP = ADP.  Plays a role in shedding (Pupovac and Sluyter 2016).  There are eight mammalian P2Y receptor subtypes (P2Y1, P2Y2, P2Y4, P2Y6, P2Y11, P2Y12, P2Y13, and P2Y14), and they play a variety of roles in cell physiology (von Kügelgen and Hoffmann 2016).  The 3-d x-ray structure of a P2Y2 receptor is known (Jacobson et al. 2015).  Antagonists stabilize an ionic lock within the P2T1 receptor, but binding of ADP breaks this ionic lock, forming a continuous water channel that leads to P2Y1 receptor activation (Yuan et al. 2016).