Mahmmoud Y A, Vorum H, Cornelius F
Department of Biophysics and Medical Biochemistry, University of Aarhus, DK-8000 Aarhus C, Denmark.
J Biol Chem. 2000 Nov 17;275(46):35969-77. doi: 10.1074/jbc.M005168200.
The Na,K-ATPase provides the driving force for many ion transport processes through control of Na(+) and K(+) concentration gradients across the plasma membranes of animal cells. It is composed of two subunits, alpha and beta. In many tissues, predominantly in kidney, it is associated with a small ancillary component, the gamma-subunit that plays a modulatory role. A novel 15-kDa protein, sharing considerable homology to the gamma-subunit and to phospholemman (PLM) was identified in purified Na,K-ATPase preparations from rectal glands of the shark Squalus acanthias, but was absent in pig kidney preparations. This PLM-like protein from shark (PLMS) was found to be a substrate for both PKA and PKC. Antibodies to the Na, K-ATPase alpha-subunit coimmunoprecipitated PLMS. Purified PLMS also coimmunoprecipitated with the alpha-subunit of pig kidney Na, K-ATPase, indicating specific association with different alpha-isoforms. Finally, PLMS and the alpha-subunit were expressed in stoichiometric amounts in rectal gland membrane preparations. Incubation of membrane bound Na,K-ATPase with non-solubilizing concentrations of C(12)E(8) resulted in functional dissociation of PLMS from Na,K-ATPase and increased the hydrolytic activity. The same effects were observed after PKC phosphorylation of Na,K-ATPase membrane preparations. Thus, PLMS may function as a modulator of shark Na,K-ATPase in a way resembling the phospholamban regulation of the Ca-ATPase.
钠钾ATP酶通过控制动物细胞质膜两侧的钠（Na⁺）和钾（K⁺）浓度梯度，为许多离子转运过程提供驱动力。它由α和β两个亚基组成。在许多组织中，主要是在肾脏中，它与一个小的辅助成分γ亚基相关联，γ亚基起调节作用。在姥鲨直肠腺纯化的钠钾ATP酶制剂中鉴定出一种与γ亚基和磷酸受磷蛋白（PLM）具有相当同源性的新型15 kDa蛋白，但在猪肾制剂中不存在。发现这种来自鲨鱼的类PLM蛋白（PLMS）是蛋白激酶A（PKA）和蛋白激酶C（PKC）的底物。抗钠钾ATP酶α亚基的抗体共免疫沉淀了PLMS。纯化的PLMS也与猪肾钠钾ATP酶的α亚基共免疫沉淀，表明与不同的α同工型有特异性关联。最后，PLMS和α亚基在直肠腺膜制剂中以化学计量的量表达。用非增溶浓度的辛基葡糖苷（C₁₂E₈）孵育膜结合的钠钾ATP酶，导致PLMS与钠钾ATP酶功能解离，并增加水解活性。在钠钾ATP酶膜制剂进行PKC磷酸化后也观察到相同的效果。因此，PLMS可能以类似于磷酸受磷蛋白对钙ATP酶的调节方式，作为姥鲨钠钾ATP酶的调节剂发挥作用。
