Chen P X, Mathews P M, Good P J, Rossier B C, Geering K
Institute of Pharmacology and Toxicology, University of Lausanne, CH-1005 Lausanne, Switzerland.
Am J Physiol. 1998 Jul;275(1):C139-45. doi: 10.1152/ajpcell.1998.275.1.C139.
The catalytic alpha-subunit of oligomeric P-type ATPases such as Na-K-ATPase and H-K-ATPase requires association with a beta-subunit after synthesis in the endoplasmic reticulum (ER) to become stably expressed and functionally active. In this study, we have expressed the beta-subunit of Xenopus gastric H-K-ATPase (betaHK) in Xenopus oocytes together with alpha-subunits of H-K-ATPase (alphaHK) or Na-K-ATPase (alphaNK) and have followed the biosynthesis, assembly, and cell surface expression of functional pumps. Immunoprecipitations of Xenopus betaHK from metabolically labeled oocytes show that it is well expressed and, when synthesized without alpha-subunits, can leave the ER and become fully glycosylated. Xenopus betaHK can associate with both coexpressed alphaHK and alphaNK, but the alpha-beta complexes formed are degraded rapidly in or close to the ER and do not produce functional pumps at the cell surface as assessed by 86Rb uptake. A possible explanation of these results is that Xenopus betaHK may contain a tissue-specific signal that is important in the formation or correct targeting of functional alpha-beta complexes in the stomach but that cannot be recognized in Xenopus oocytes and in consequence leads to cellular degradation of the alpha-beta complexes in this experimental system.
诸如钠钾ATP酶和氢钾ATP酶等寡聚P型ATP酶的催化α亚基在内质网（ER）中合成后需要与β亚基结合，才能稳定表达并具有功能活性。在本研究中，我们已在非洲爪蟾卵母细胞中共同表达了非洲爪蟾胃氢钾ATP酶的β亚基（βHK）与氢钾ATP酶（αHK）或钠钾ATP酶（αNK）的α亚基，并追踪了功能性泵的生物合成、组装及细胞表面表达。从经代谢标记的卵母细胞中免疫沉淀非洲爪蟾βHK表明其表达良好，并且在没有α亚基的情况下合成时，它可以离开内质网并完全糖基化。非洲爪蟾βHK可以与共表达的αHK和αNK结合，但形成的α-β复合物在内质网内或内质网附近迅速降解，并且如通过86Rb摄取所评估的那样，不会在细胞表面产生功能性泵。这些结果的一个可能解释是，非洲爪蟾βHK可能含有一种组织特异性信号，该信号在胃中功能性α-β复合物的形成或正确靶向中很重要，但在非洲爪蟾卵母细胞中无法被识别，因此导致该实验系统中α-β复合物的细胞降解。
