Unidad de Investigación UNAM-INC, Facultad de Medicina, Universidad Nacional Autónoma de México, Mexico City, Mexico.
Departamento de Nefrología y Metabolismo Mineral, Instituto Nacional de Ciencias Médicas y Nutrición Salvador Zubirán, Mexico City, Mexico.
Am J Physiol Cell Physiol. 2023 Oct 1;325(4):C921-C939. doi: 10.1152/ajpcell.00089.2023. Epub 2023 Aug 7.
The solute carrier family 12A (SLC12A) superfamily of membrane transporters modulates the movement of cations coupled with chloride across the membrane. In doing so, these cotransporters are involved in numerous aspects of human physiology: cell volume regulation, ion homeostasis, blood pressure regulation, and neurological action potential via intracellular chloride concentration modulation. Their physiological characterization has been largely studied; however, understanding the mechanics of their function and the relevance of structural domains or specific amino acids has been a pending task. In recent years, single-particle cryogenic electron microscopy (cryo-EM) has been successfully applied to members of the SLC12A family including all K:Cl cotransporters (KCCs), Na:K:2Cl cotransporter NKCC1, and recently Na:Cl cotransporter (NCC); revealing structural elements that play key roles in their function. The present review analyzes the data provided by these cryo-EM reports focusing on structural domains and specific amino acids involved in ion binding, domain interactions, and other important SCL12A structural elements. A comparison of cryo-EM data from NKCC1 and KCCs is presented in the light of the two recent NCC cryo-EM studies, to propose insight into structural elements that might also be found in NCC and are necessary for its proper function. In the final sections, the importance of key coordination residues for substrate specificity and their implication on various pathophysiological conditions and genetic disorders is reviewed, as this could provide the basis to correlate structural elements with the development of novel and selective treatments, as well as mechanistic insight into the function and regulation of cation-coupled chloride cotransporters (CCCs).
溶质载体家族 12A（SLC12A）家族的膜转运蛋白调节阳离子与氯离子跨膜的共同转运。通过这种方式，这些共转运蛋白参与了许多人类生理学方面：细胞体积调节、离子稳态、血压调节和通过细胞内氯离子浓度调节的神经动作电位。它们的生理学特征已经得到了广泛的研究；然而，理解它们功能的机制以及结构域或特定氨基酸的相关性一直是一个悬而未决的任务。近年来，单颗粒低温电子显微镜（cryo-EM）已成功应用于 SLC12A 家族的成员，包括所有 K：Cl 共转运体（KCCs）、Na：K：2Cl 共转运体 NKCC1，以及最近的 Na：Cl 共转运体（NCC）；揭示了在其功能中起关键作用的结构元素。本综述分析了这些 cryo-EM 报告提供的数据，重点关注参与离子结合、结构域相互作用和其他重要 SCL12A 结构元素的结构域和特定氨基酸。根据最近的两项 NCC cryo-EM 研究，对 NKCC1 和 KCCs 的 cryo-EM 数据进行了比较，提出了对结构元素的深入了解，这些结构元素也可能存在于 NCC 中，并且对其正常功能是必要的。在最后几节中，综述了关键配位残基对底物特异性的重要性及其对各种病理生理条件和遗传疾病的影响，这可能为将结构元素与新型和选择性治疗方法的发展以及对阳离子偶联氯离子共转运体（CCCs）的功能和调节的机制性理解联系起来提供基础。
