Structure-dynamic and functional relationships in a Li+-transporting sodiumcalcium exchanger mutant.
Biochim Biophys Acta Bioenerg
; 1860(3): 189-200, 2019 03 01.
Article
em En
| MEDLINE
| ID: mdl-30414928
ABSTRACT
The cell membrane (NCX) and mitochondrial (NCLX) Na+/Ca2+ exchangers control Ca2+ homeostasis. Eleven (out of twelve) ion-coordinating residues are highly conserved among eukaryotic and prokaryotic NCXs, whereas in NCLX, nine (out of twelve) ion-coordinating residues are different. Consequently, NCXs exhibit high selectivity for Na+ and Ca2+, whereas NCLX can exchange Ca2+ with either Na+ or Li+. However, the underlying molecular mechanisms and physiological relevance remain unresolved. Here, we analyzed the NCX_Mj-derived mutant NCLX_Mj (with nine substituted residues) imitating the ion selectivity of NCLX. Site-directed fluorescent labeling and ion flux assays revealed the nearly symmetric accessibility of ions to the extracellular and cytosolic vestibules in NCLX_Mj (Kintâ¯=â¯0.8-1.4), whereas the extracellular vestibule is predominantly accessible to ions (Kintâ¯=â¯0.1-0.2) in NCX_Mj. HDX-MS (hydrogen-deuterium exchange mass-spectrometry) identified symmetrically rigidified core helix segments in NCLX_Mj, whereas the matching structural elements are asymmetrically rigidified in NCX_Mj. The HDX-MS analyses of ion-induced conformational changes and the mutational effects on ion fluxes revealed that the "Ca2+-site" (SCa) of NCLX_Mj binds Na+, Li+, or Ca2+, whereas one or more additional Na+/Li+ sites of NCLX_Mj are incompatible with the Na+ sites (Sext and Sint) of NCX_Mj. Thus, the replacement of ion-coordinating residues in NCLX_Mj alters not only the ion selectivity of NCLX_Mj, but also the capacity and affinity for Na+/Li+ (but not for Ca2+) binding, bidirectional ion-accessibility, the response of the ion-exchange to membrane potential changes, and more. These structure-controlled functional features could be relevant for differential contributions of NCX and NCLX to Ca2+ homeostasis in distinct sub-cellular compartments.
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Texto completo:
1
Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Transporte de Íons
/
Trocador de Sódio e Cálcio
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Proteínas Mutantes
/
Lítio
Tipo de estudo:
Prognostic_studies
Idioma:
En
Revista:
Biochim Biophys Acta Bioenerg
Ano de publicação:
2019
Tipo de documento:
Article