A molecular coupling mechanism for the oxaloacetate decarboxylase Na+ pump as inferred from mutational analysis.
A molecular coupling mechanism for the oxaloacetate decarboxylase Na+ pump as inferred from mutational analysis.
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DOI：
10.1021/bi992261v
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发表时间：
2000-03
期刊：
影响因子：
2.9
通讯作者：
P. Jockel;M. Schmid;J. Steuber;P. Dimroth
中科院分区：
文献类型：
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作者：
P. Jockel;M. Schmid;J. Steuber;P. Dimroth
草酰乙酸脱羧酶Na+泵由α、β和γ亚基组成，并含有生物素作为辅基。膜结合的亚基β催化羧基生物素的脱羧耦合Na+易位，并消耗周质衍生的质子。跨膜螺旋VIII的保守氨基酸的定点诱变表明残基N373、G377、S382和R389在功能上是重要的。这些氨基酸的极性侧基可以与D2O3一起构成可电离基团的网络，其促进Na+和相反取向的H+跨膜的移位。有证据表明，两个Na+离子结合的亚基β在运输过程中与D203和S382作为结合位点。钠离子从细胞质结合到这两个网站elanimated脱羧的羧基生物素，和构象开关暴露的结合Na+离子朝向周质。在Na+解离和H+结合后，细胞质暴露的构象恢复。
The oxaloacetate decarboxylase Na+ pump consists of subunits alpha, beta, and gamma, and contains biotin as the prosthetic group. Membrane-bound subunit beta catalyzes the decarboxylation of carboxybiotin coupled to Na+ translocation, and consumes a periplasmically derived proton. Site-directed mutagenesis of conserved amino acids of transmembrane helix VIII indicated that residues N373, G377, S382, and R389 are functionally important. The polar side groups of these amino acids may constitute together with D203 a network of ionizable groups which promotes the translocation of Na+ and the oppositely oriented H+ across the membrane. Evidence is presented that two Na+ ions are bound simultaneously to subunit beta during transport with D203 and S382 acting as binding sites. Sodium ion binding from the cytoplasm to both sites elicits decarboxylation of carboxybiotin, and a conformational switch exposes the bound Na+ ions toward the periplasm. After dissociation of Na+ and binding of H+, the cytoplasmically exposed conformation is regained.