Papineni Rao V L, O'Connell Kristen M S, Zhang Hongwei, Dirksen Robert T, Hamilton Susan L
Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, Texas 77030, USA.
J Biol Chem. 2002 Dec 20;277(51):49167-74. doi: 10.1074/jbc.M209564200. Epub 2002 Oct 2.
Apocalmodulin and Ca(2+) calmodulin bind to overlapping sites on the ryanodine receptor skeletal form, RYR1, but have opposite functional effects on channel activity. Suramin, a polysulfonated napthylurea, displaces both forms of calmodulin, leading to an inhibition of activity at low Ca(2+) and an enhancement of activity at high Ca(2+). Calmodulin binding motifs on RYR1 are also able to directly interact with the carboxy-terminal tail of the transverse tubule dihydropyridine receptor (DHPR) (Sencer, S., Papineni, R. V., Halling, D. B., Pate, P., Krol, J., Zhang, J. Z., and Hamilton, S. L. (2001) J. Biol. Chem. 276, 38237-38241). Suramin binds directly to a peptide that corresponds to the calmodulin binding site of RYR1 (amino acids 3609-3643) and blocks the interaction of this peptide with both calmodulin and the carboxyl-terminal tail of the DHPR alpha(1)-subunit. Suramin, added to the internal solution of voltage-clamped skeletal myotubes, produces a concentration-dependent increase in the maximal magnitude of voltage-gated Ca(2+) transients without significantly altering L-channel Ca(2+) channel conducting activity. Together, these results suggest that an interaction between the carboxyl-terminal tail of the DHPR alpha(1)-subunit with the calmodulin binding region of RYR1 serves to limit sarcoplasmic reticulum Ca(2+) release during excitation-contraction coupling and that suramin-induced potentiation of voltage-gated Ca(2+) release involves a relief of this inhibitory interaction.
载脂蛋白钙调蛋白和Ca(2+)钙调蛋白与兰尼碱受体骨骼肌型（RYR1）上的重叠位点结合，但对通道活性具有相反的功能作用。苏拉明是一种多磺酸化萘脲，可取代两种形式的钙调蛋白，导致在低Ca(2+)浓度下抑制活性，而在高Ca(2+)浓度下增强活性。RYR1上的钙调蛋白结合基序也能够直接与横管二氢吡啶受体（DHPR）的羧基末端尾部相互作用（森瑟，S.，帕皮尼尼，R.V.，哈林，D.B.，佩特，P.，克罗尔，J.，张，J.Z.，和汉密尔顿，S.L.（2001年）《生物化学杂志》276，38237 - 38241）。苏拉明直接与对应于RYR1钙调蛋白结合位点的肽（氨基酸3609 - 3643）结合，并阻断该肽与钙调蛋白以及DHPRα(1)亚基羧基末端尾部的相互作用。将苏拉明添加到电压钳制的骨骼肌管内溶液中，会使电压门控Ca(2+)瞬变的最大幅度产生浓度依赖性增加，而不会显著改变L型通道Ca(2+)通道的传导活性。总之，这些结果表明，DHPRα(1)亚基的羧基末端尾部与RYR1的钙调蛋白结合区域之间的相互作用在兴奋 - 收缩偶联过程中限制了肌浆网Ca(2+)的释放，并且苏拉明诱导的电压门控Ca(2+)释放增强涉及这种抑制性相互作用的解除。
