Z. lysine (D12K) and cysteine (D12C). As expected, wild-type PLM significantly slows channel activation and deactivation and 1,2-Dipalmitoyl-sn-glycerol 3-phosphate enhances voltage-dependent inactivation (VDI). We were surprised to find that amino acid substitutions at Thr-10 and Asp-12 significantly enhanced the ability of PLM to modulate CaV1.2 gating. T10A exhibited a twofold enhancement of PLM-induced slowing of activation, whereas D12K and D12C dramatically enhanced PLM-induced increase of VDI. The PLM-induced slowing of channel closing was abrogated by D12A and D12C, whereas D12K and T10A failed to impact this effect. These studies demonstrate that this PFXYD motif is not necessary for the association of PLM with CaV1.2. Instead, since altering the chemical and/or physical properties of the PFXYD segment alters the relative magnitudes of opposing PLM-induced effects on CaV1.2 channel gating, PLM appears to play an important role in fine tuning the gating kinetics of cardiac calcium channels and likely plays an important role in shaping the cardiac action potential and regulating Ca2+dynamics in the heart. Keywords:FXYD1, Cav1.2, activation, deactivation, inactivation the fxyd familyof ion 1,2-Dipalmitoyl-sn-glycerol 3-phosphate transport regulators were first defined by Sweadner and Rael (29) based on an invariant peptide Mouse monoclonal to CD105 sequence known as the FXYD motif. The FXYD motif is localized around the NH2-termini of these single membrane spanning proteins and consists of five amino acids (Pro-Phe-X-Tyr-Asp). Seven users of the FXYD family (FXYD1 through FXYD7) have been recognized in mammals and are widely distributed in tissues that perform fluid and solute transport (kidney, colon, breast/mammary gland, pancreas, prostate, liver, lung, and placenta) and in electrically excitable tissues (nervous system and muscle mass). One role of the FXYD family of ion transport regulators is to act as tissue-specific auxiliary subunits of Na-K-ATPase (NKA), which is the principal enzyme regulating the distribution of Na+and K+concentration across cell membranes (6,8,12,29). FXYD1, also known as phospholemman (PLM), consists of a single transmembrane segment flanked by 17 amino acid extracellular NH2-terminal and 36 amino acid intracellular COOH-terminal domains (21). PLM is usually abundantly expressed in the cardiac sarcolemma, where it has been shown to modulate NKA (7,10,15,27,37) and the Na+/Ca2+exchanger (NCX) (1,19,28,31,32,36,38). We recently exhibited that PLM associates with and alters the gating behavior of L-type calcium channels (33). Ca2+access through L-type calcium channels is an important first step that leads to myocardial contraction. The dysregulation of this process can lead to severe cardiac pathologies such as Long QT syndrome (35). The modulation of L-type calcium channels by signaling pathways and associated 1,2-Dipalmitoyl-sn-glycerol 3-phosphate proteins is important for many physiological and pathophysiological processes (5,20,25). Their importance in maintaining normal heart function is further exhibited by their value as drug targets for the treatment of heart disease (14,24). The cardiac L-type calcium channel is a heteromultimeric complex consisting of 1-, -, and 2-subunits (18) and the ubiquitous Ca2+-sensing protein calmodulin (22). The 1-subunit (CaV1.2) contains the major pore-forming and gating domains required for its function, the – and 2-subunits are involved in trafficking the channel to the plasma membrane and modulation of certain gating functions (5,18), and calmodulin is important for promoting Ca2+-dependent changes in gating such as Ca2+-dependent facilitation and Ca2+-dependent inactivation (22). Thus CaV1.2-associated proteins such as PLM represent an important mechanism by which the cardiac action potential and Ca2+influx during the cardiac action potential and cardiac function can be regulated. The high degree of conservation of the PFXYD motif among all its family members in a wide range of species indicates that selective pressure has prevented this motif from undergoing spontaneous mutations. This rationale 1,2-Dipalmitoyl-sn-glycerol 3-phosphate is usually supported by structural studies of the NKA //FXYD10 complex that 1,2-Dipalmitoyl-sn-glycerol 3-phosphate suggest aromatic residues in the FXYD motif may play a role in stabilizing the association between NKA – and -subunits (26). With each other, these observations.