Department of Physiology, David Geffen School of Medicine at UCLA, Los Angeles, California 90095-1751, USA.
J Biol Chem. 2012 Mar 9;287(11):8652-9. doi: 10.1074/jbc.M111.331280. Epub 2012 Jan 27.
The superfamily of cation/Ca(2+) exchangers includes both Na(+)/Ca(2+) exchangers (NCXs) and Na(+)/Ca(2+),K(+) exchangers (NCKX) as the families characterized in most detail. These Ca(2+) transporters have prominent physiological roles. For example, NCX and NCKX are important in regulation of cardiac contractility and visual processes, respectively. The superfamily also has a large number of members of the YrbG family expressed in prokaryotes. However, no members of this family have been functionally expressed, and their transport properties are unknown. We have expressed, purified, and characterized a member of the YrbG family, MaX1 from Methanosarcina acetivorans. MaX1 catalyzes Ca(2+) uptake into membrane vesicles. The Ca(2+) uptake requires intravesicular Na(+) and is stimulated by an inside positive membrane potential. Despite very limited sequence similarity, MaX1 is a Na(+)/Ca(2+) exchanger with kinetic properties similar to those of NCX. The availability of a prokaryotic Na(+)/Ca(2+) exchanger should facilitate structural and mechanistic investigations.
阳离子/Ca(2+)交换器超家族包括 Na(+)/Ca(2+)交换器 (NCX) 和 Na(+)/Ca(2+),K(+)交换器 (NCKX)，这两个家族是研究最详细的家族。这些 Ca(2+)转运蛋白具有重要的生理作用。例如，NCX 和 NCKX 在心脏收缩和视觉过程的调节中分别起着重要作用。该超家族还在原核生物中有大量 YrbG 家族成员。然而，该家族的成员尚未被功能表达，其转运特性尚不清楚。我们已经表达、纯化并表征了 Methanosarcina acetivorans 中的 YrbG 家族成员 MaX1。MaX1 催化 Ca(2+)进入膜囊泡的摄取。Ca(2+)摄取需要囊内 Na(+)，并且受膜内正电势的刺激。尽管序列相似性非常有限，但 MaX1 是一种 Na(+)/Ca(2+)交换器，其动力学特性与 NCX 相似。原核 Na(+)/Ca(2+)交换器的可用性应有助于结构和机制的研究。
