1
|
Moore JR, Campbell SG, Lehman W. Structural determinants of muscle thin filament cooperativity. Arch Biochem Biophys 2016; 594:8-17. [PMID: 26891592 DOI: 10.1016/j.abb.2016.02.016] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2015] [Revised: 02/09/2016] [Accepted: 02/10/2016] [Indexed: 11/16/2022]
Abstract
End-to-end connections between adjacent tropomyosin molecules along the muscle thin filament allow long-range conformational rearrangement of the multicomponent filament structure. This process is influenced by Ca(2+) and the troponin regulatory complexes, as well as by myosin crossbridge heads that bind to and activate the filament. Access of myosin crossbridges onto actin is gated by tropomyosin, and in the case of striated muscle filaments, troponin acts as a gatekeeper. The resulting tropomyosin-troponin-myosin on-off switching mechanism that controls muscle contractility is a complex cooperative and dynamic system with highly nonlinear behavior. Here, we review key information that leads us to view tropomyosin as central to the communication pathway that coordinates the multifaceted effectors that modulate and tune striated muscle contraction. We posit that an understanding of this communication pathway provides a framework for more in-depth mechanistic characterization of myopathy-associated mutational perturbations currently under investigation by many research groups.
Collapse
Affiliation(s)
- Jeffrey R Moore
- Department of Biological Sciences, University of Massachusetts Lowell, One University Avenue, Lowell, MA 018154, USA
| | - Stuart G Campbell
- Department of Biomedical Engineering, Yale University, 55 Prospect Street, New Haven, CT 06511, USA
| | - William Lehman
- Department of Physiology & Biophysics, Boston University School of Medicine, 72 East Concord Street, Boston, MA 02118, USA.
| |
Collapse
|
2
|
Gupte TM, Haque F, Gangadharan B, Sunitha MS, Mukherjee S, Anandhan S, Rani DS, Mukundan N, Jambekar A, Thangaraj K, Sowdhamini R, Sommese RF, Nag S, Spudich JA, Mercer JA. Mechanistic heterogeneity in contractile properties of α-tropomyosin (TPM1) mutants associated with inherited cardiomyopathies. J Biol Chem 2014; 290:7003-15. [PMID: 25548289 DOI: 10.1074/jbc.m114.596676] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The most frequent known causes of primary cardiomyopathies are mutations in the genes encoding sarcomeric proteins. Among those are 30 single-residue mutations in TPM1, the gene encoding α-tropomyosin. We examined seven mutant tropomyosins, E62Q, D84N, I172T, L185R, S215L, D230N, and M281T, that were chosen based on their clinical severity and locations along the molecule. The goal of our study was to determine how the biochemical characteristics of each of these mutant proteins are altered, which in turn could provide a structural rationale for treatment of the cardiomyopathies they produce. Measurements of Ca(2+) sensitivity of human β-cardiac myosin ATPase activity are consistent with the hypothesis that hypertrophic cardiomyopathies are hypersensitive to Ca(2+) activation, and dilated cardiomyopathies are hyposensitive. We also report correlations between ATPase activity at maximum Ca(2+) concentrations and conformational changes in TnC measured using a fluorescent probe, which provide evidence that different substitutions perturb the structure of the regulatory complex in different ways. Moreover, we observed changes in protein stability and protein-protein interactions in these mutants. Our results suggest multiple mechanistic pathways to hypertrophic and dilated cardiomyopathies. Finally, we examined a computationally designed mutant, E181K, that is hypersensitive, confirming predictions derived from in silico structural analysis.
Collapse
Affiliation(s)
- Tejas M Gupte
- From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India
| | - Farah Haque
- From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India, the National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India
| | - Binnu Gangadharan
- From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India, the Manipal University, Madhav Nagar, Manipal 576104, India
| | - Margaret S Sunitha
- From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India, the National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India
| | - Souhrid Mukherjee
- From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India
| | - Swetha Anandhan
- From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India
| | - Deepa Selvi Rani
- the Council for Scientific and Industrial Research-Centre for Cellular and Molecular Biology, Hyderabad 500007, India
| | - Namita Mukundan
- the National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India
| | - Amruta Jambekar
- From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India
| | - Kumarasamy Thangaraj
- the Council for Scientific and Industrial Research-Centre for Cellular and Molecular Biology, Hyderabad 500007, India
| | - Ramanathan Sowdhamini
- the National Centre for Biological Sciences, Tata Institute of Fundamental Research, Bangalore 560065, India
| | - Ruth F Sommese
- the Department of Biochemistry, Stanford University School of Medicine, Stanford, California 94305, and
| | - Suman Nag
- the Department of Biochemistry, Stanford University School of Medicine, Stanford, California 94305, and
| | - James A Spudich
- From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India, the Department of Biochemistry, Stanford University School of Medicine, Stanford, California 94305, and
| | - John A Mercer
- From the Institute for Stem Cell Biology and Regenerative Medicine, Bangalore 560065, India, the McLaughlin Research Institute, Great Falls, Montana 59405
| |
Collapse
|
3
|
Energy landscapes reveal the myopathic effects of tropomyosin mutations. Arch Biochem Biophys 2014; 564:89-99. [PMID: 25241052 DOI: 10.1016/j.abb.2014.09.007] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2014] [Revised: 09/03/2014] [Accepted: 09/09/2014] [Indexed: 11/24/2022]
Abstract
Striated muscle contraction is regulated by an interaction network connecting the effects of troponin, Ca(2+), and myosin-heads to the azimuthal positioning of tropomyosin along thin filaments. Many missense mutations, located at the actin-tropomyosin interface, however, reset the regulatory switching mechanism either by weakening or strengthening residue-specific interactions, leading to hyper- or hypo-contractile pathologies. Here, we compute energy landscapes for the actin-tropomyosin interface and quantify contributions of single amino acid residues to actin-tropomyosin binding. The method is a useful tool to assess effects of actin and tropomyosin mutations, potentially relating initial stages of myopathy to alterations in thin filament stability and regulation. Landscapes for mutant filaments linked to hyper-contractility provide a simple picture that describes a decrease in actin-tropomyosin interaction energy. Destabilizing the blocked (relaxed)-state parallels previously noted enhanced Ca(2+)-sensitivity conferred by these mutants. Energy landscapes also identify post-translational modifications that can rescue regulatory imbalances. For example, cardiomyopathy-associated E62Q tropomyosin mutation weakens actin-tropomyosin interaction, but phosphorylation of neighboring S61 rescues the binding-deficit, results confirmed experimentally by in vitro motility assays. Unlike results on hyper-contractility-related mutants, landscapes for tropomyosin mutants tied to hypo-contractility do not present a straightforward picture. These mutations may affect other components of the regulatory network, e.g., troponin-tropomyosin signaling.
Collapse
|