STRUCTURE/FUNCTION OF CARDIAC SODIUM/CALCIUM EXCHANGE

肌膜Na ~+-Ca ~（2+）交换是主要的Ca ~（2+）外排机制 在心肌细胞中。 因此，交换器在热交换中具有关键作用。 调节心肌收缩力。分子知识 重要的转运蛋白将有助于了解正常和疾病 心中 这项研究的长期目标是阐明 Na+-Ca 2+交换剂的结构和功能，以更好地了解 运输的机制和规则。 为实现这一目标，具体目标如下：1.离子移位。 Na+和Ca 2+通过交换的运动途径 蛋白质将被确定。 半胱氨酸扫描诱变将是 开始分析氨基酸残基在 假设跨膜片段在离子交换中是重要的 易位 巯基作用的系统分析 半胱氨酸突变体上的试剂将有助于确定残基可及性 并将提供有关易位结构的信息 途径（例如，孔隙宽度和深度; α-螺旋度）。 进一步 芳香族残基、含羟基残基的诱变，以及 还计划在交换剂之间保留残基。 变种人将会 在非洲爪蟾卵母细胞中表达，并通过测量45 Ca 2 + 通量和交换电流。2.调控Na+-Ca 2+交换剂是 受到各种复杂的管制。 例如，交换器 通过非转运Ca 2+与高亲和力 胞内位点。 此外，交换器具有自动调节功能， 区域，有一个锚定结合位点，并受到阴离子刺激， 磷脂如PIP 2。 这些现象的分子基础 可以使用蛋白质生物化学、分子生物学、 生物学和电生理学。 3.结构次级方案的各个方面 Na+-Ca 2+交换蛋白的三级结构将是 测定 拓扑将通过各种技术进行评估。 一 利用半胱氨酸诱变和蛋白质结合的项目 生物化学也开始确定α- 膜内的螺旋

The sarcolemmal Na+-Ca2+ exchanger is the dominant Ca2+ efflux mechanism in myocardial cells. Thus, the exchanger has a critical role in the regulation of myocardial contractility. Molecular knowledge of this essential transporter will help understand both normal and diseased hearts. The long-term objective of this research is to elucidate the structure and function of the Na+-Ca2+ exchanger to better understand the mechanism and regulation of transport. Toward this goal, specific aims are as follows: 1. Ion translocation. The pathway for the movement of Na+ and Ca2+ through the exchange protein will be determined. Cysteine-scanning mutagenesis will be initiated to analyze the importance of amino acids residues in transmembrane segments hypothesized to be important in ion translocation. Systematic analysis of the effects of sulfhydryl reagents on cysteine mutants will help determine residue accessibility and will provide information on the structure of the translocation pathway (e.g., pore width and depth; alpha-helicity). Further mutagenesis of aromatic residues, hydroxyl-containing residues, and residues conserved among exchangers is also planned. Mutants will be expressed in Xenopus oocytes and assessed by measurements of 45Ca2+ fluxes and exchange currents. 2. Regulation. The Na+-Ca2+ exchanger is subject to diverse and complex regulation. For example, the exchanger is regulated by the binding of nontransported Ca2+ to a high affinity intracellular site. In addition, the exchanger has an autoregulatory region, has an ankyrin-binding site, and is stimulated by anionic phospholipids such as PIP2. The molecular bases of these phenomena will be determined using a combination of protein biochemistry, molecular biology, and electrophysiology. 3. Structure. Aspects of the secondary and tertiary structure of the Na+-Ca2+ exchange protein will be determined. Topology will be assessed by a variety of techniques. A project using a combination of cysteine mutagenesis and protein biochemistry is also being initiated to determine the packing of alpha- helices within the membrane.