Long-Range Allosteric Regulation of Pumps and Transporters: What Can We Learn from Mammalian NCX Antiporters?

摘要: The Ca2+-dependent allosteric regulation of ion-channels, pumps, and transporters is still a subject multidisciplinary research due to its fundamental significance. mammalian Na+/Ca2+ exchangers (NCX1–3) their splice-variants are expressed in tissue-specific manner extrude Ca2+ diverse cell types. Since NCX proteins involved regulating numerous physiological pathophysiological events, selective pharmacological targeting long-wanted objective, although this intervention remains challenging our poor understanding the underlying mechanisms. Eukaryotic NCXs strongly regulated by cytosolic [Ca2+] oscillations, where interacts with regulatory domains, CBD1 CBD2. Recent evidence suggests that CBD1–CBD2 interface controls Ca2+driven tethering CBDs, which associated occlusion (and slow dissociation) at primary sensor (Ca3–Ca4 sites), thereby driving dynamic coupling CBDs. This mechanism seems be common for all isoform/splice variants. on highly conserved among variants, whereas “tissue-specific” splicing segment located CBD2 modifies not only affinity kinetic properties Ca3–Ca4 sites but also essence signal, resulting either activation, inhibition, or no response given variant. By using hydrogen-deuterium exchange mass-spectrometry (HDX-MS), small-angle X-ray scattering (SAXS), equilibrium 45Ca2+ binding, stopped-flow techniques, we found binding rigidifies backbone flexibility (but CBD1), stabilizes apo-CBD1 structure. extent strength rigidification splice-variant dependent, spans from up tip (>50 A), alternatively, it stops helix splice variant exhibiting inhibitory Ca2+. These findings provide structure-dynamic basis alternative diversifies responses propagation signals over long distances.