פרופ' דניאל חננשבילי

Associate Professor, Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel Aviv University

Education

Mechanisms, Regulation and Pharmacology of Calcium Transporting NCX Proteins

Calcium (Ca2+) is a major regulator in the living cell. In many cell-types the Na+/Ca2+ exchanger proteins (NCX) represent a major Ca2+ extruding system and thus, play a key role in regulating the Ca2+-dependent events in the cell. Three NCX genes form numerous splice variants, which are expressed in a tissue-specific manner to regulate excitation–contraction coupling in heart, long-term potentiation and learning in brain, blood pressure, immune responses, neurotransmitter and hormone secretion, kidney Ca2+ reabsorption, mitochondrial bioenergetics, etc. Altered expression and regulation of NCX proteins is a chief contributor to Ca2+-driven tissue-remodeling in heart failure, cerebral ischemia, hypertension, diabetes, renal malfunction, muscle dystrophy, etc. For example, in cardiac disease a single isoform/splice variant (NCX1.1) is overexpressed, thereby representing a primary concern for life-threating arrhythmias and contractile malfunction. Selective pharmacological targeting of NCX variants is expected to recover Ca2+ homeostasis in predefined cell types and thus, may improve desired activity of altered tissues/organs.

Since this breakthrough remains challenging our research efforts are focused on two principle issues: a) To resolve structure-activity relationships underlying the function and regulation of diverse NCX variants; b) To develop new experimental approaches for selective pharmacological targeting of tissue-specific NCX variants with a goal of providing new opportunities for preventing and effective treatment of harmful diseases. In this respect we investigate structure-activity relationships in the wild-type and mutated proteins by exploring a wide spectrum of techniques (stopped-flow and ion-flux assays, FRET, SAXS, ITC, X-ray crystallography, confocal microscopy, patch-clamp, etc). In searching the regulatory mechanisms of CBD1 and CBD2 domains we found that the tissue-specific splice segment, located on CBD2, shapes the regulatory specificity of the primary Ca2+ sensor located on CBD1. These findings may allow the identification of drug candidates targeting the disease-related NCX variants.

Publications

Marinelli F, Almagor L, Hiller R, Giladi M, Khananshvili D*, and Faraldo-Gómez JD. Sodium recognition by the Na⁺/Ca²⁺ exchanger in the outward-facing conformation. (*Corresponding Author). Proc Natl Acad Sci USA, 2014, doi:10.1073/pnas.1415751111

Giladi M, Lee S-Y, Hiller R, Chung K-Y, and Khananshvili, D. Structure-dynamic determinants governing a mode of regulatory response and propagation of allosteric signal in splice variants of Na⁺/Ca²⁺ exchange (NCX) proteins. Biochem J, doi:10.1042/BJ20141036

Almagor L, Giladi M, van Dijk L, Buki T, Hiller R, and Khananshvili D. Functional asymmetry of bidirectional ca²⁺-movements in an archaeal sodium-calcium exchanger (NCX_Mj). Cell Calcium 2014, 56:276-284.

Giladi M, Michaely L, Almagor A, Bar-On D, Buki T, Ashery U, Khananshvili, Hirsch JA. The C2B domain is the primary Ca²⁺ sensor in DOC2B: A structural and functional analysis. J Mol Biol, 2013, 425:4629–4641.

Giladi M, Hiller R, Hirsch JA, Khananshvili D. Population shift underlies Ca²⁺-induced regulatory transitions in the sodium-calcium exchanger (NCX). J Biol Chem, 2013, 288:23141-23149.

Giladi, M. and Khananshvili, D. Molecular determinants of allosteric regulation in NCX proteins. Adv Exp Med and Biol, 2013, 961:35-48.

Khananshvili D, Binah O, Attali B. The Ca²⁺-activated K⁺ channel IKCa/SK4: a critical new player in human embryonic cardiac pacemaker. Proc Natl Acad Sci USA, 2013, 110:1685-1694.

Nita II, Hershfinkel M, Fishman D, Ozeri E, Rutter GA, Sensi SL, Khananshvili D, Lewis EC, Sekler I. The mitochondrial Na⁺/Ca²⁺ exchanger upregulates glucose dependent Ca²⁺ signaling linked to insulin secretion. PloS One 2012, 7:e46649.

Giladi M, Friedberg I, Fang X, Hiller R, Wang YX, Khananshvili D. G503 is obligatory for coupling of regulatory domains in NCX proteins. Biochemistry 2012, 51:7313-720.

Giladi, M., Bohbot, H., Buki, T., Schulze, D. H., Hiller, R. and Khananshvili, D. Dynamic features of allosteric Ca²⁺ sensor in tissue-specific NCX variants. Cell Calcium, 51:478-485, 2012.

Giladi M, Sasson Y, Fang X, Hiller R, Buki T, Wang Y-X, Hirsch JA and Khananshvili D. A common Ca²⁺-driven interdomain module governs eukaryotic NCX regulation. PloS One, 7:e39985. 2012

Boyman L, Hagen BM, Giladi M, Hiller R, WJ Lederer and Khananshvili D. Proton-Sensing Ca²⁺ Binding Domains Regulate the Cardiac Na⁺/Ca²⁺ Exchanger. J Biol Chem, 286:28811-28820, 2011. 

Giladi M, Boyman L, Mikhasenko H, Hiller R and Khananshvili D. Essential role of the CBD1-CBD2 linker in slow dissociation of Ca²⁺ from the regulatory two-domain tandem of NCX1. J BiolChem 285:28117–28125, 2010.

Palty R, Silverman WF, Hershfinkel M, Caporale T, Sensi SL, Parnis J, Nolte C, Fishman, D., Shoshan-Barmatz V, Herrmann S, Khananshvili D and Sekler I. NCLX is an essential component of mitochondrial Na⁺/Ca²⁺ exchange. Proc Natl Acad Sci USA 107:436-441, 2010.

Reviews

Khananshvili, D. Sodium-Calcium Exchangers (NCX): Molecular Hallmarks Underlying Tissue-Specific and Systemic Functions, Pflügers Arch (in press)

Khananshvili, D. SLC8 gene family of sodium-calcium exchangers (NCX): Structure, function and regulation in health and disease. Mol Asp Med 34:220-35, 2013.

Giladi, M. and Khananshvili, D. (2013) Molecular determinants of allosteric regulation in NCX proteins. Adv Exp Med Biol 961:35-48.

Boyman L, GSB Williams, Khananshvili D, Sekler I, WJ Lederer. NCLX: The mitochondrial sodium calcium exchanger. J Mol Cell Cardiology 2013, 59:205-213.

Grants

2013-2017       Fields Center of Molecular Cardiology

2010-2015       USA-Israel Binational Science Foundation   

2014-2018       Israeli Science Foundation