Abstract
The relative ease of introducing a paramagnetic species onto a protein, and advances in electron paramagnetic resonance (EPR) over the past two decades, have established spin labeling as a vital structural biology technique for revealing the functional workings of the troponin muscle regulatory complex—an ~80 kDa heterotrimeric protein switch for turning on striated muscle contraction. Through the site-directed spin labeling (SDSL) of cysteine residues at key sites in troponin, a molecular-level understanding of the troponin muscle regulatory system across all levels of structural hierarchy has been achieved. Through the application of EPR, mobility and accessibility trends in the EPR signals of the spin labels attached to consecutive residues can reveal the secondary structure of troponin elements and also help map the interaction between subunits. Distance restraints calculated from the interspin interactions between spin label pairs have helped with building a structural model of the troponin complex. Further, when SDSL is paired with NMR, paramagnetic relaxation enhancement (PRE)-NMR has been used to obtain high-resolution structural detail for both intra- and interdomain interactions in troponin and revealed details of protein conformational changes and dynamics accompanying troponin function. In this review, we provide an overview of the SDSL labeling methodology and its application towards building a dynamic structural model of the multi-subunit troponin complex which details the calcium-induced conformational changes intimately linked to muscle regulation. We also describe how the SDSL method, in conjunction with EPR or NMR, can be used to obtain insights into structural perturbations to troponin caused by disease-causing mutations.
Similar content being viewed by others
References
Abe J, Ueki S, Yamauchi S, Arata T, Ohba Y (2018) Double quantum coherence EPR reveals the structure–function relationships of the cardiac troponin C–troponin I complex regulated by Ca2+ ions and a phosphomimetic. Appl Magn Reson 49:893–910
Aihara T, Ueki S, Nakamura M, Arata T (2006) Calcium-dependent movement of troponin I between troponin C and actin as revealed by spin-labeling EPR. Biochem Biophys Res Commun 340:462–468
Aihara T, Nakamura M, Ueki S, Hara H, Miki M, Arata T (2010) Switch action of troponin on muscle thin filament as revealed by spin labeling and pulsed EPR. J Biol Chem 285:10671–10677
Altenbach C, Flitsch SL, Khorana HG, Hubbell WL (1989) Structural studies on transmembrane proteins. 2. Spin labeling of bacteriorhodopsin mutants at unique cysteines. Biochemistry 28:7806–7812
Altenbach C, Marti T, Khorana HG, Hubbell WL (1990) Transmembrane protein structure: spin labeling of bacteriorhodopsin mutants. Science 248:1088–1092
Arata T, Aihara T, Ueda K, Nakamura M, Ueki S (2007) Calcium structural transition of troponin in the complexes, on the thin filament, and in muscle fibres, as studied by site-directed spin-labelling EPR. Adv Exp Med Biol 592:125–135
Banham JE, Baker CM, Ceola S, Day IJ, Grant GH, Groenen EJ, Rodgers CT, Jeschke G, Timmel CR (2008) Distance measurements in the borderline region of applicability of CW EPR and DEER: a model study on a homologous series of spin-labelled peptides. J Magn Reson 191:202–218
Battiste JL, Wagner G (2000) Utilization of site-directed spin labeling and high-resolution heteronuclear nuclear magnetic resonance for global fold determination of large proteins with limited nuclear Overhauser effect data. Biochemistry 39:5355–5365
Behrmann E, Muller M, Penczek PA, Mannherz HG, Manstein DJ, Raunser S (2012) Structure of the rigor actin-tropomyosin-myosin complex. Cell 150:327–338
Blumenschein TM, Stone DB, Fletterick RJ, Mendelson RA, Sykes BD (2005) Calcium-dependent changes in the flexibility of the regulatory domain of troponin C in the troponin complex. J Biol Chem 280:21924–21932
Bodor GS, Oakeley AE, Allen PD, Crimmins DL, Ladenson JH, Anderson PA (1997) Troponin I phosphorylation in the normal and failing adult human heart. Circulation 96:1495–1500
Borbat PP, McHaourab HS, Freed JH (2002) Protein structure determination using long-distance constraints from double-quantum coherence ESR: study of T4 lysozyme. J Am Chem Soc 124:5304–5314
Bordignon E, Bleicken S (2018) New limits of sensitivity of site-directed spin labeling electron paramagnetic resonance for membrane proteins. Biochim Biophys Acta Biomembr 1860:841–853
Brown LJ, Sale KL, Hills R, Rouviere C, Song L, Zhang X, Fajer PG (2002) Structure of the inhibitory region of troponin by site directed spin labeling electron paramagnetic resonance. Proc Natl Acad Sci U S A 99:12765–12770
Chatani S, Nakamura M, Akahane H, Kohyama N, Taki M, Arata T, Yamamoto Y (2005) Synthesis of C2-chiral bifunctionalised spin labels and their application to troponin C. Chem Commun (Camb) 14:1880–1882
Clore GM, Iwahara J (2009) Theory, practice, and applications of paramagnetic relaxation enhancement for the characterization of transient low-population states of biological macromolecules and their complexes. Chem Rev 109:4108–4139
Cooke JA, Brown LJ (2011) Distance measurements by continuous wave EPR spectroscopy to monitor protein folding. In: Hill AF, Barnham KJ, Bottomley SP, Cappai R (eds) Protein folding, Misfolding, and disease: methods and protocols. Humana Press, Totowa, NJ, pp 73–96
Cooke JA, Chamoun J, Howell MW, Curmi PMG, Fajer PG, Brown LJ (2010) Structure and dynamics of the mobile domain of troponin I by SDSL-EPR. Biophysical J 98:148a
Cordina NM, Liew CK, Gell DA, Fajer PG, Mackay JP, Brown LJ (2012) Interdomain orientation of cardiac troponin C characterized by paramagnetic relaxation enhancement NMR reveals a compact state. Protein Sci 21:1376–1387
Cordina NM, Liew CK, Gell DA, Fajer PG, Mackay JP, Brown LJ (2013) Effects of calcium binding and the hypertrophic cardiomyopathy A8V mutation on the dynamic equilibrium between closed and open conformations of the regulatory N-domain of isolated cardiac troponin C. Biochemistry 52:1950–1962
Cordina NM, Liew CK, Potluri PR, Curmi PM, Fajer PG, Logan TM, Mackay JP, Brown LJ (2014) Ca2+-induced PRE-NMR changes in the troponin complex reveal the possessive nature of the cardiac isoform for its regulatory switch. PLoS One 9:e112976
Dong W, Rosenfeld SS, Wang CK, Gordon AM, Cheung HC (1996) Kinetic studies of calcium binding to the regulatory site of troponin C from cardiac muscle. J Biol Chem 271:688–694
Dong WJ, Xing J, Robinson JM, Cheung HC (2001) Ca2+ induces an extended conformation of the inhibitory region of troponin I in cardiac muscle troponin. J Mol Biol 314:51–61
Evans EG, Millhauser GL (2015) Genetic incorporation of the unnatural amino acid p-acetyl phenylalanine into proteins for site-directed spin labeling. Methods Enzymol 563:503–527
Fajer PG, Brown LJ, Song L (2007) Practical pulsed dipolar ESR (DEER). In: Hemminga MA, Berliner L (eds) ESR spectroscopy in membrane biophysics. Springer US, New York, pp 95–128
Findlay WA, Sonnichsen FD, Sykes BD (1994) Solution structure of the TR1C fragment of skeletal muscle troponin-C. J Biol Chem 269:6773–6778
Gagne SM, Tsuda S, Li MX, Smillie LB, Sykes BD (1995) Structures of the troponin C regulatory domains in the apo and calcium-saturated states. Nat Struct Biol 2:784–789
Gagne SM, Li MX, McKay RT, Sykes BD (1998) The NMR angle on troponin C. Biochem Cell Biol 76:302–312
Gomes AV, Potter JD (2004) Molecular and cellular aspects of troponin cardiomyopathies. Ann N Y Acad Sci 1015:214–224
Gordon AM, Homsher E, Regnier M (2000) Regulation of contraction in striated muscle. Physiol Rev 80:853–924
Herzberg O, James MN (1985) Structure of the calcium regulatory muscle protein troponin-C at 2.8 A resolution. Nature 313:653–659
Howarth JW, Meller J, Solaro RJ, Trewhella J, Rosevear PR (2007) Phosphorylation-dependent conformational transition of the cardiac specific N-extension of troponin I in cardiac troponin. J Mol Biol 373:706–722
Hubbell WL, Gross A, Langen R, Lietzow MA (1998) Recent advances in site-directed spin labeling of proteins. Curr Opin Struct Biol 8:649–656
Hubbell WL, Lopez CJ, Altenbach C, Yang Z (2013) Technological advances in site-directed spin labeling of proteins. Curr Opin Struct Biol 23:725–733
Jeschke G (2012) DEER distance measurements on proteins. Annu Rev Phys Chem 63:419–446
Jeschke G (2018) MMM: a toolbox for integrative structure modeling. Protein Sci 27:76–85
Kim CH, Axup JY, Schultz PG (2013) Protein conjugation with genetically encoded unnatural amino acids. Curr Opin Chem Biol 17:412–419
Layland J, Solaro RJ, Shah AM (2005) Regulation of cardiac contractile function by troponin I phosphorylation. Cardiovasc Res 66:12–21
Li HC, Fajer PG (1994) Orientational changes of troponin C associated with thin filament activation. Biochemistry 33:14324–14332
Li HC, Fajer PG (1998) Structural coupling of troponin C and actomyosin in muscle fibers. Biochemistry 37:6628–6635
Li HC, Hideg K, Fajer PG (1997) The mobility of troponin C and troponin I in muscle. J Mol Recognit 10:194–201
Li KL, Rieck D, Solaro RJ, Dong W (2014) In situ time-resolved FRET reveals effects of sarcomere length on cardiac thin-filament activation. Biophys J 107:682–693
Liang B, Bushweller JH, Tamm LK (2006) Site-directed parallel spin-labeling and paramagnetic relaxation enhancement in structure determination of membrane proteins by solution NMR spectroscopy. J Am Chem Soc 128:4389–4397
McHaourab HS, Lietzow MA, Hideg K, Hubbell WL (1996) Motion of spin-labeled side chains in T4 lysozyme. Correlation with protein structure and dynamics. Biochemistry 35:7692–7704
McHaourab HS, Oh KJ, Fang CJ, Hubbell WL (1997) Conformation of T4 lysozyme in solution. Hinge-bending motion and the substrate-induced conformational transition studied by site-directed spin labeling. Biochemistry 36:307–316
McNulty JC, Silapie JL, Carnevali M, Farrar CT, Griffin RG, Formaggio F, Crisma M, Toniolo C, Millhauser GL (2000) Electron spin resonance of TOAC labeled peptides: folding transitions and high frequency spectroscopy. Biopolymers 55:479–485
Miick SM, Martinez GV, Fiori WR, Todd AP, Millhauser GL (1992) Short alanine-based peptides may form 310-helices and not alpha-helices in aqueous solution. Nature 359:653–655
Milov AD, Salikhov KM, Shirov M (1981) Application of ELDOR in electron spin echo for paramagnetic center spin distributions in solids. Fiz Tverd Tela 23:975–982
Milov AD, Mar'yasov AG, Samoilova RI, Tsvetkov YD, Raap J, Monaco V, Formaggio F, Crisma M, Toniolo C (2000) Pulsed electron double resonance of spin-labeled peptides: data on the peptide-chain secondary structure. Dokl Biochem 370:8–11
Murakami K, Yumoto F, Ohki SY, Yasunaga T, Tanokura M, Wakabayashi T (2005) Structural basis for Ca2+-regulated muscle relaxation at interaction sites of troponin with actin and tropomyosin. J Mol Biol 352:178–201
Nakamura M, Ueki S, Hara H, Arata T (2005) Calcium structural transition of human cardiac troponin C in reconstituted muscle fibres as studied by site-directed spin labelling. J Mol Biol 348:127–137
Narita A, Yasunaga T, Ishikawa T, Mayanagi K, Wakabayashi T (2001) Ca2+-induced switching of troponin and tropomyosin on actin filaments as revealed by electron cryo-microscopy. J Mol Biol 308:241–261
Potluri PR, Chamoun J, Cooke JA, Badr M, Guse JA, Rayes R, Cordina NM, McCamey D, Fajer PG, Brown LJ (2017) The concerted movement of the switch region of troponin I in cardiac muscle thin filaments as tracked by conventional and pulsed (DEER) EPR. J Struct Biol 200:376–387
Potluri PR, Cordina NM, Kachooei E, Brown LJ (2019) Characterization of the L29Q hypertrophic cardiomyopathy mutation in cardiac troponin C by paramagnetic relaxation enhancement nuclear magnetic resonance. Biochemistry 58:908–917
Rabenstein MD, Shin YK (1995) Determination of the distance between two spin labels attached to a macromolecule. Proc Natl Acad Sci U S A 92:8239–8243
Risi C, Eisner J, Belknap B, Heeley DH, White HD, Schroder GF, Galkin VE (2017) Ca2+-induced movement of tropomyosin on native cardiac thin filaments revealed by cryoelectron microscopy. Proc Natl Acad Sci U S A 114:6782–6787
Sia SK, Li MX, Spyracopoulos L, Gagne SM, Liu W, Putkey JA, Sykes BD (1997) Structure of cardiac muscle troponin C unexpectedly reveals a closed regulatory domain. J Biol Chem 272:18216–18221
Slupsky CM, Sykes BD (1995) NMR solution structure of calcium-saturated skeletal muscle troponin C. Biochemistry 34:15953–15964
Solaro RJ, Henze M, Kobayashi T (2013) Integration of troponin I phosphorylation with cardiac regulatory networks. Circ Res 112:355–366
Sun YB, Brandmeier B, Irving M (2006) Structural changes in troponin in response to Ca2+ and myosin binding to thin filaments during activation of skeletal muscle. Proc Natl Acad Sci U S A 103:17771–17776
Sundaralingam M, Bergstrom R, Strasburg G, Rao ST, Roychowdhury P, Greaser M, Wang BC (1985) Molecular structure of troponin C from chicken skeletal muscle at 3-angstrom resolution. Science 227:945–948
Sykes BD (2003) Pulling the calcium trigger. Nat Struct Biol 10:588–589
Syska H, Wilkinson JM, Grand RJ, Perry SV (1976) The relationship between biological activity and primary structure of troponin I from white skeletal muscle of the rabbit. Biochem J 153:375–387
Szczesna D, Fajer PG (1995) The tropomyosin domain is flexible and disordered in reconstituted thin filaments. Biochemistry 34:3614–3620
Takeda S, Yamashita A, Maeda K, Maeda Y (2003) Structure of the core domain of human cardiac troponin in the Ca2+-saturated form. Nature 424:35–41
Tao T, Gong BJ, Leavis PC (1990) Calcium-induced movement of troponin-I relative to actin in skeletal muscle thin filaments. Science 247:1339–1341
Tsuda S, Miura A, Gagne SM, Spyracopoulos L, Sykes BD (1999) Low-temperature-induced structural changes in the apo regulatory domain of skeletal muscle troponin C. Biochemistry 38:5693–5700
Tung CS, Wall ME, Gallagher SC, Trewhella J (2000) A model of troponin-I in complex with troponin-C using hybrid experimental data: the inhibitory region is a beta-hairpin. Protein Sci 9:1312–1326
Ueki S, Nakamura M, Komori T, Arata T (2005) Site-directed spin labeling electron paramagnetic resonance study of the calcium-induced structural transition in the N-domain of human cardiac troponin C complexed with troponin I. Biochemistry 44:411–416
Vassylyev DG, Takeda S, Wakatsuki S, Maeda K, Maeda Y (1998) Crystal structure of troponin C in complex with troponin I fragment at 2.3-Å resolution. Proc Natl Acad Sci U S A 95:4847–4852
Vibert P, Craig R, Lehman W (1997) Steric-model for activation of muscle thin filaments. J Mol Biol 266:8–14
Vinogradova MV, Stone DB, Malanina GG, Karatzaferi C, Cooke R, Mendelson RA, Fletterick RJ (2005) Ca2+-regulated structural changes in troponin. Proc Natl Acad Sci U S A 102:5038–5043
Volkov AN, Worrall JA, Holtzmann E, Ubbink M (2006) Solution structure and dynamics of the complex between cytochrome c and cytochrome c peroxidase determined by paramagnetic NMR. Proc Natl Acad Sci U S A 103:18945–18950
Wijnker PJ, Murphy AM, Stienen GJ, van der Velden J (2014) Troponin I phosphorylation in human myocardium in health and disease. Neth Heart J 22:463–469
Willott RH, Gomes AV, Chang AN, Parvatiyar MS, Pinto JR, Potter JD (2010) Mutations in troponin that cause HCM, DCM AND RCM: what can we learn about thin filament function? J Mol Cell Cardiol 48:882–892
Acknowledgements
EK is supported by a Macquarie University International Post Graduate Research Award. The authors would like to thank Dr. Phani Potluri (Macquarie University) for many helpful discussions.
Author information
Authors and Affiliations
Corresponding author
Ethics declarations
Conflict of interest
Ehsan Kachooei declares that he has no conflict of interest. Nicole M. Cordina declares that she has no conflict of interest. Louise J. Brown declares that she has no conflict of interest.
Ethical approval
This article does not contain any studies with human participants or animals performed by any of the authors.
Additional information
Publisher’s note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
This article is part of a Special Issue on ‘Biophysics & Structural Biology at Synchrotrons’ edited by Trevor Sewell.
Rights and permissions
About this article
Cite this article
Kachooei, E., Cordina, N.M. & Brown, L.J. Constructing a structural model of troponin using site-directed spin labeling: EPR and PRE-NMR. Biophys Rev 11, 621–639 (2019). https://doi.org/10.1007/s12551-019-00568-5
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s12551-019-00568-5