S100A1 is a member of the S100 family of proteins expressed in cardiac muscle, skeletal muscle, and the brain,[7] with the highest density at Z-lines and the sarcoplasmic reticulum.[8] In its dimerized form, S100A1 contains four EF-handcalcium-binding motifs,[9] and can exist as either a heterodimer or a homodimer. The homodimer is a high-affinity complex (nanomolar range or tighter) stabilized by hydrophobic packing within an X-type four-helix bundle formed by helices 1, 1′, 4, and 4′.
Protein nuclear magnetic resonance spectroscopy shows that each monomer is helical and contains two EF-hand loops: one in the N-terminus and a canonical EF-hand in the C-terminus. The C-terminal site has higher calcium affinity, with a dissociation constant of about 20 µM. The two EF-hands are positioned adjacent to each other in three-dimensional space and are linked by a short beta sheet (residues 27–29 and 68–70). Calcium binding triggers a conformational change in helix 3, which reorients from being nearly antiparallel to helix 4 to being roughly perpendicular. This mechanism is atypical among EF-hand proteins because the entering helix moves rather than the exiting one. The rearrangement exposes a large hydrophobic pocket between helices 3, 4, and the hinge region, which mediates most calcium-dependent target interactions.
These structural features are generally conserved across the S100 family, although helices 3, 4, and the hinge region are the most divergent areas. Sequence variation in these regions likely fine-tunes calcium-dependent target binding specificity.[10]S-Nitrosylation of Cys85 further modifies the protein by reorganizing the C-terminal helix and the linker connecting the two EF-hands.[11] The most accurate high-resolution solution structure of human apo-S100A1 (PDB accession code: 2L0P) was determined by NMR spectroscopy in 2011.[12]
In addition to Ca²⁺, S100A1 also binds Zn²⁺. Mass spectrometry and isothermal titration calorimetry show up to four Zn²⁺ ions per monomer, with two high-affinity sites located within the EF-hands and two lower-affinity sites outside them. Zn²⁺ competes with Ca²⁺ at the EF-hands, producing mixed 2Ca²⁺:S100A1:2Zn²⁺ species under saturating conditions. QM/MM modeling suggests that the N-terminal EF-hand favors Zn²⁺, while the C-terminal site can accommodate both metals. Functionally, Ca²⁺ binding increases thermal stability, whereas excess Zn²⁺ destabilizes the protein and promotes aggregation. Despite this, S100A1 remains dimeric across all tested metal concentrations.[13]
During development, S100A1 is expressed in the primitive heart at embryonic day 8 at similar levels in both atria and ventricles. By embryonic day 17.5, expression becomes enriched in the ventricular myocardium and reduced in atrial tissue.[14]
In humans, reduced myocardial S100A1 expression has been linked to cardiomyopathies.[27] Importantly, left ventricular assist device therapy does not restore myocardial S100A1 levels in patients with end-stage heart failure.[28]
S100A1 regulates endothelial cell function, where its deficiency impairs post-ischemic angiogenesis. Downregulation has been observed in hypoxic tissue from patients with limb ischemia.[29][30] In melanocytic cells, S100A1 expression may also be regulated by MITF.[31]
Therapeutic potential
Therapeutic strategies have investigated S100A1 gene transfer. In a rat model of myocardial infarction, intracoronary adenoviral delivery of S100A1 restored Ca2+ handling, normalized intracellular sodium, reversed fetal gene expression, preserved contractility, reduced hypertrophy, and improved inotropic reserve.[32][33] Similarly, transgenic overexpression of S100A1 in mice subjected to infarction preserved contractility, Ca2+ cycling, and β-adrenergic signaling, while preventing hypertrophy, apoptosis, and progression to heart failure, ultimately improving survival.[34][35] Gene transfer to engineered heart tissue has also been shown to enhance contractile performance of tissue grafts, suggesting potential applications in regenerative therapy.[36]
Biomarker potential
S100A1 has also been studied as a diagnostic and prognostic biomarker. Plasma levels rise early during acute myocardial ischemia, with a distinct timecourse compared to creatine kinase, CKMB, and troponin I.[37] After ischemic injury, S100A1 is released from cardiomyocytes and can signal through Toll-like receptor 4 to modulate myocardial damage.[38] Extracellular S100A1 also protects neonatal murine cardiomyocytes against apoptosis through ERK1/2-dependent pathways, suggesting that release from injured cells may function as an intrinsic survival mechanism.[39] Elevated S100A1 has also been observed during cardiopulmonary bypass, both in infants with cyanotic heart disease undergoing uncontrolled hyperoxic reoxygenation[40] and in adults undergoing cardiac surgery.[41]
S100A1 has emerged as a promising therapeutic target in heart failure research. Preclinical studies in large animal models and experiments on failing human cardiomyocytes have demonstrated that restoring S100A1 expression can reverse contractile dysfunction, normalize Ca2+ signalling, and improve overall myocardial performance.[42] In a large-animal model of post-ischemic heart failure, cardiac-specific delivery of S100A1 via an AAV9 vector restored contractile reserve and prevented adverse remodeling.[43] These findings highlight the translational potential of S100A1-based therapy.
S100A1 is a multifaceted therapeutic target that bridges basic cardiac physiology and clinical application.[44][45][46][47] Collectively, these works propose that S100A1 modulates multiple aspects of cardiac physiology, including excitation–contraction coupling, β-adrenergic signaling, and mitochondrial energy metabolism.
Because of these pleiotropic effects, S100A1 gene therapy has been positioned as a potentially safer and more durable alternative to conventional heart failure drugs, which often target single signaling pathways. Preclinical data suggest that viral-mediated S100A1 delivery not only enhances contractility but also prevents maladaptive hypertrophy, apoptosis, and progression to heart failure.[48] Current expert consensus places S100A1-based therapy “on the verge” of early clinical trials, with the potential to become part of a new generation of gene-based strategies for treating advanced heart failure.[49][50]
↑ Morii K, Tanaka R, Takahashi Y, Minoshima S, Fukuyama R, Shimizu N, etal. (February 1991). "Structure and chromosome assignment of human S100 alpha and beta subunit genes". Biochemical and Biophysical Research Communications. 175 (1): 185–191. Bibcode:1991BBRC..175..185M. doi:10.1016/S0006-291X(05)81218-5. PMID1998503.
↑ Engelkamp D, Schäfer BW, Erne P, Heizmann CW (October 1992). "S100 alpha, CAPL, and CACY: molecular cloning and expression analysis of three calcium-binding proteins from human heart". Biochemistry. 31 (42): 10258–10264. doi:10.1021/bi00157a012. PMID1384693.
↑ Marenholz I, Heizmann CW, Fritz G (October 2004). "S100 proteins in mouse and man: from evolution to function and pathology (including an update of the nomenclature)". Biochemical and Biophysical Research Communications. 322 (4): 1111–1122. Bibcode:2004BBRC..322.1111M. doi:10.1016/j.bbrc.2004.07.096. PMID15336958.
↑ Remppis A, Most P, Löffler E, Ehlermann P, Bernotat J, Pleger S, etal. (2002). "The small EF-hand Ca2+ binding protein S100A1 increases contractility and Ca2+ cycling in rat cardiac myocytes". Basic Research in Cardiology. 97 Suppl 1 (7): I56 –I62. doi:10.1007/s003950200031. PMID12479236. S2CID25461816.
↑ Kettlewell S, Most P, Currie S, Koch WJ, Smith GL (December 2005). "S100A1 increases the gain of excitation-contraction coupling in isolated rabbit ventricular cardiomyocytes". Journal of Molecular and Cellular Cardiology. 39 (6): 900–910. doi:10.1016/j.yjmcc.2005.06.018. PMID16236309.
↑ Völkers M, Loughrey CM, Macquaide N, Remppis A, DeGeorge BR, Wegner FV, etal. (February 2007). "S100A1 decreases calcium spark frequency and alters their spatial characteristics in permeabilized adult ventricular cardiomyocytes". Cell Calcium. 41 (2): 135–143. doi:10.1016/j.ceca.2006.06.001. PMID16919727.
↑ Tsoporis JN, Marks A, Zimmer DB, McMahon C, Parker TG (January 2003). "The myocardial protein S100A1 plays a role in the maintenance of normal gene expression in the adult heart". Molecular and Cellular Biochemistry. 242 (1–2): 27–33. doi:10.1023/A:1021148503861. PMID12619862. S2CID12957638.
↑ Remppis A, Pleger S, Most P, Lindenkamp J, Ehlermann P, Schweda C, etal. (April 2004). "S100A1 gene transfer: a strategy to strengthen engineered cardiac grafts". The Journal of Gene Medicine. 6 (4): 387–394. doi:10.1002/jgm.513. PMID15079813. S2CID30629576.
↑ Kiewitz R, Acklin C, Minder E, Huber P, Schäfer B, Heizmann C (11 August 2000). "S100A1, a new marker for acute myocardial ischemia". Biochemical and Biophysical Research Communications. 274 (3): 865–871. Bibcode:2000BBRC..274..865K. doi:10.1006/bbrc.2000.3229. PMID10924368.
↑ Matheis G, Abdel-Rahman U, Braun S, Wimmer-Greinecker G, Esmaili A, Seitz U, etal. (October 2000). "Uncontrolled reoxygenation by initiating cardiopulmonary bypass is associated with higher protein S100 in cyanotic versus acyanotic patients". The Thoracic and Cardiovascular Surgeon. 48 (5): 263–268. doi:10.1055/s-2000-7879. PMID11100757. S2CID260335126.
↑ Brett W, Mandinova A, Remppis A, Sauder U, Rüter F, Heizmann C, etal. (15 June 2001). "Translocation of S100A1(1) calcium binding protein during heart surgery". Biochemical and Biophysical Research Communications. 284 (3): 698–703. Bibcode:2001BBRC..284..698B. doi:10.1006/bbrc.2001.4996. PMID11396958.
↑ Rohde D, Brinks H, Ritterhoff J, Qui G, Ren S, Most P (May 2011). "S100A1 gene therapy for heart failure: a novel strategy on the verge of clinical trials". Journal of Molecular and Cellular Cardiology. 50 (5): 777–784. doi:10.1016/j.yjmcc.2010.08.012. PMID20732326.
↑ Yang Q, O'Hanlon D, Heizmann CW, Marks A (February 1999). "Demonstration of heterodimer formation between S100B and S100A6 in the yeast two-hybrid system and human melanoma". Experimental Cell Research. 246 (2): 501–509. doi:10.1006/excr.1998.4314. PMID9925766.
1 2 Kiewitz R, Acklin C, Schäfer BW, Maco B, Uhrík B, Wuytack F, etal. (June 2003). "Ca2+ -dependent interaction of S100A1 with the sarcoplasmic reticulum Ca2+ -ATPase2a and phospholamban in the human heart". Biochemical and Biophysical Research Communications. 306 (2): 550–557. doi:10.1016/s0006-291x(03)00987-2. PMID12804600.
↑ Most P, Boerries M, Eicher C, Schweda C, Völkers M, Wedel T, etal. (January 2005). "Distinct subcellular location of the Ca2+-binding protein S100A1 differentially modulates Ca2+-cycling in ventricular rat cardiomyocytes". Journal of Cell Science. 118 (Pt 2): 421–431. doi:10.1242/jcs.01614. PMID15654019. S2CID33063596.
Schäfer BW, Heizmann CW (April 1996). "The S100 family of EF-hand calcium-binding proteins: functions and pathology". Trends in Biochemical Sciences. 21 (4): 134–140. doi:10.1016/S0968-0004(96)80167-8. PMID8701470.
Engelkamp D, Schäfer BW, Erne P, Heizmann CW (October 1992). "S100 alpha, CAPL, and CACY: molecular cloning and expression analysis of three calcium-binding proteins from human heart". Biochemistry. 31 (42): 10258–10264. doi:10.1021/bi00157a012. PMID1384693.
Morii K, Tanaka R, Takahashi Y, Minoshima S, Fukuyama R, Shimizu N, etal. (February 1991). "Structure and chromosome assignment of human S100 alpha and beta subunit genes". Biochemical and Biophysical Research Communications. 175 (1): 185–191. Bibcode:1991BBRC..175..185M. doi:10.1016/S0006-291X(05)81218-5. PMID1998503.
Kato K, Kimura S (October 1985). "S100ao (alpha alpha) protein is mainly located in the heart and striated muscles". Biochimica et Biophysica Acta (BBA) - General Subjects. 842 (2–3): 146–150. doi:10.1016/0304-4165(85)90196-5. PMID4052452.
Schäfer BW, Wicki R, Engelkamp D, Mattei MG, Heizmann CW (February 1995). "Isolation of a YAC clone covering a cluster of nine S100 genes on human chromosome 1q21: rationale for a new nomenclature of the S100 calcium-binding protein family". Genomics. 25 (3): 638–643. doi:10.1016/0888-7543(95)80005-7. PMID7759097.
Treves S, Scutari E, Robert M, Groh S, Ottolia M, Prestipino G, etal. (September 1997). "Interaction of S100A1 with the Ca2+ release channel (ryanodine receptor) of skeletal muscle". Biochemistry. 36 (38): 11496–11503. doi:10.1021/bi970160w. PMID9298970.
Mandinova A, Atar D, Schäfer BW, Spiess M, Aebi U, Heizmann CW (July 1998). "Distinct subcellular localization of calcium binding S100 proteins in human smooth muscle cells and their relocation in response to rises in intracellular calcium". Journal of Cell Science. 111 ( Pt 14) (14): 2043–2054. doi:10.1242/jcs.111.14.2043. PMID9645951.
Osterloh D, Ivanenkov VV, Gerke V (August 1998). "Hydrophobic residues in the C-terminal region of S100A1 are essential for target protein binding but not for dimerization". Cell Calcium. 24 (2): 137–151. doi:10.1016/S0143-4160(98)90081-1. PMID9803314.
Garbuglia M, Verzini M, Donato R (September 1998). "Annexin VI binds S100A1 and S100B and blocks the ability of S100A1 and S100B to inhibit desmin and GFAP assemblies into intermediate filaments". Cell Calcium. 24 (3): 177–191. doi:10.1016/S0143-4160(98)90127-0. PMID9883272.
1k2h: Three-dimensional Solution Structure of apo-S100A1.
1zfs: Solution structure of S100A1 bound to calcium
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