1
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Burghardt TP. Natural variant frequencies across domains from different sarcomere proteins cross-correlate to identify inter-protein contacts associated with cardiac muscle function and disease. MOLECULAR BIOMEDICINE 2021; 2:35. [PMID: 35006463 PMCID: PMC8607394 DOI: 10.1186/s43556-021-00056-x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2021] [Accepted: 09/23/2021] [Indexed: 12/15/2022] Open
Abstract
Coordinated sarcomere proteins produce contraction force for muscle shortening. In human ventriculum they include the cardiac myosin motor (βmys), repetitively converting ATP free energy into work, and myosin binding protein C (MYBPC3) that in complex with βmys is regulatory. Single nucleotide variants (SNVs) causing hereditary heart diseases frequently target this protein pair. The βmys/MYBPC3 complex models a regulated motor and is used here to study how the proteins couple. SNVs in βmys or MYBPC3 survey human populations worldwide. Their protein expression modifies domain structure affecting phenotype and pathogenicity outcomes. When the SNV modified domain locates to inter-protein contacts it could affect complex coordination. Domains involved, one in βmys the other in MYBPC3, form coordinated domains (co-domains). Co-domain bilateral structure implies the possibility for a shared impact from SNV modification in either domain suggesting a correlated response to a common perturbation could identify their location. Genetic divergence over human populations is proposed to perturb SNV probability coupling that is detected by cross-correlation in 2D correlation genetics (2D-CG). SNV probability data and 2D-CG identify three critical sites, two in MYBPC3 with links to several domains across the βmys motor, and, one in βmys with links to the MYBPC3 regulatory domain. MYBPC3 sites are hinges sterically enabling regulatory interactions with βmys. The βmys site is the actin binding C-loop (residues 359-377). The C-loop is a trigger for actin-activated myosin ATPase and a contraction velocity modulator. Co-domain identification implies their spatial proximity suggesting a novel approach for in vivo protein complex structure determination.
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Affiliation(s)
- Thomas P Burghardt
- Department of Biochemistry and Molecular Biology, Mayo Clinic Rochester, 200 First St. SW, Rochester, MN, 55905, USA.
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2
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Burghardt TP. Demographic model for inheritable cardiac disease. Arch Biochem Biophys 2019; 672:108056. [PMID: 31356777 DOI: 10.1016/j.abb.2019.07.021] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2019] [Revised: 07/24/2019] [Accepted: 07/25/2019] [Indexed: 11/15/2022]
Abstract
The cardiac muscle proteins, generating and regulating energy transduction during a heartbeat, assemble in the sarcomere into a cyclical machine repetitively translating actin relative to myosin filaments. Myosin is the motor transducing ATP free energy into actin movement against resisting force. Cardiac myosin binding protein C (mybpc3) regulates shortening velocity probably by transient N-terminus binding to actin while its C-terminus strongly binds the myosin filament. Inheritable heart disease associated mutants frequently modify these proteins involving them in disease mechanisms. Nonsynonymous single nucleotide polymorphisms (SNPs) cause single residue substitutions with independent characteristics (sequence location, residue substitution, human demographic, and allele frequency) hypothesized to decide dependent phenotype and pathogenicity characteristics in a feed-forward neural network model. Trial models train and validate on a dynamic worldwide SNP database for cardiac muscle proteins then predict phenotype and pathogenicity for any single residue substitution in myosin, mybpc3, or actin. A separate Bayesian model formulates conditional probabilities for phenotype or pathogenicity given independent SNP characteristics. Neural/Bayes forecasting tests SNP pathogenicity vs (in)dependent SNP characteristics to assess individualized disease risk and in particular to elucidate gender and human subpopulation bias in disease. Evident subpopulation bias in myosin SNP pathogenicities imply myosin normally engages multiple sarcomere proteins functionally. Consistent with this observation, mybpc3 forms a third actomyosin interaction competing with myosin essential light chain N-terminus suggesting a novel strain-dependent mechanism adapting myosin force-velocity to load dynamics. The working models, and the integral myosin/mybpc3 motor concept, portends the wider considerations involved in understanding heart disease as a systemic maladaptation.
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Affiliation(s)
- Thomas P Burghardt
- Department of Biochemistry and Molecular Biology and Physiology and Biomedical Engineering, 200 First St. SW, Mayo Clinic Rochester, Rochester, MN, 55905, USA.
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3
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Wang Y, Ajtai K, Burghardt TP. Cardiac and skeletal actin substrates uniquely tune cardiac myosin strain-dependent mechanics. Open Biol 2018; 8:180143. [PMID: 30463911 PMCID: PMC6282072 DOI: 10.1098/rsob.180143] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2018] [Accepted: 10/26/2018] [Indexed: 01/24/2023] Open
Abstract
Cardiac ventricular myosin (βmys) translates actin by transducing ATP free energy into mechanical work during muscle contraction. Unitary βmys translation of actin is the step-size. In vitro and in vivo βmys regulates contractile force and velocity autonomously by remixing three different step-sizes with adaptive stepping frequencies. Cardiac and skeletal actin isoforms have a specific 1 : 4 stoichiometry in normal adult human ventriculum. Human adults with inheritable hypertrophic cardiomyopathy (HCM) upregulate skeletal actin in ventriculum probably compensating the diseased muscle's inability to meet demand by adjusting βmys force-velocity characteristics. βmys force-velocity characteristics were compared for skeletal versus cardiac actin substrates using ensemble in vitro motility and single myosin assays. Two competing myosin strain-sensitive mechanisms regulate step-size choices dividing single βmys mechanics into low- and high-force regimes. The actin isoforms alter myosin strain-sensitive regulation such that onset of the high-force regime, where a short step-size is a large or major contributor, is offset to higher loads probably by the unique cardiac essential light chain (ELC) N-terminus/cardiac actin contact at Glu6/Ser358. It modifies βmys force-velocity by stabilizing the ELC N-terminus/cardiac actin association. Uneven onset of the high-force regime for skeletal versus cardiac actin modulates force-velocity characteristics as skeletal/cardiac actin fractional content increases in diseased muscle.
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Affiliation(s)
- Yihua Wang
- Department of Biochemistry and Molecular Biology, Mayo Clinic Rochester, Rochester, MN 55905, USA
| | - Katalin Ajtai
- Department of Biochemistry and Molecular Biology, Mayo Clinic Rochester, Rochester, MN 55905, USA
| | - Thomas P Burghardt
- Department of Biochemistry and Molecular Biology, Mayo Clinic Rochester, Rochester, MN 55905, USA
- Department of Physiology and Biomedical Engineering, Mayo Clinic Rochester, Rochester, MN 55905, USA
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4
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Wang Y, Burghardt TP. In vitro actin motility velocity varies linearly with the number of myosin impellers. Arch Biochem Biophys 2017; 618:1-8. [PMID: 28131772 DOI: 10.1016/j.abb.2017.01.012] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2016] [Revised: 01/23/2017] [Accepted: 01/24/2017] [Indexed: 11/26/2022]
Abstract
Cardiac myosin is the motor powering the heart. It moves actin with 3 step-size varieties generated by torque from the myosin heavy chain lever-arm rotation under the influence of myosin essential light chain whose N-terminal extension binds actin. Proposed mechanisms adapting myosin mechanochemical characteristics on the fly sometimes involve modulation of step-size selection probability via motor strain sensitivity. Strain following the power stroke, hypothetically imposed by the finite actin detachment rate 1/ton, is shown to have no effect on unloaded velocity when multiple myosins are simultaneously strongly actin bound in an in vitro motility assay. Actin filaments slide ∼2 native step-sizes while more than 1 myosin strongly binds actin probably ruling out an actin detachment limited model for imposing strain. It suggests that single myosin estimates for ton are too large, not applicable to the ensemble situation, or both. Parallel motility data quantitation involving instantaneous particle velocities (frame velocity) and actin filament track averaged velocities (track velocity) give an estimate of the random walk step-size, δ. Comparing δ for slow and fast motility components suggests the higher speed component has cardiac myosin upshifting to longer steps. Variable step-size characteristics imply cardiac myosin maintains a velocity dynamic range not involving strain.
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Affiliation(s)
- Y Wang
- Department of Biochemistry and Molecular Biology, Mayo Clinic Rochester, Rochester, MN 55905, United States
| | - T P Burghardt
- Department of Biochemistry and Molecular Biology, Mayo Clinic Rochester, Rochester, MN 55905, United States; Department of Physiology and Biomedical Engineering, Mayo Clinic Rochester, Rochester, MN 55905, United States.
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Burghardt TP, Sun X, Wang Y, Ajtai K. In vitro and in vivo single myosin step-sizes in striated muscle. J Muscle Res Cell Motil 2015; 36:463-77. [PMID: 26728749 PMCID: PMC4764389 DOI: 10.1007/s10974-015-9440-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2015] [Accepted: 12/11/2015] [Indexed: 10/22/2022]
Abstract
Myosin in muscle transduces ATP free energy into the mechanical work of moving actin. It has a motor domain transducer containing ATP and actin binding sites, and, mechanical elements coupling motor impulse to the myosin filament backbone providing transduction/mechanical-coupling. The mechanical coupler is a lever-arm stabilized by bound essential and regulatory light chains. The lever-arm rotates cyclically to impel bound filamentous actin. Linear actin displacement due to lever-arm rotation is the myosin step-size. A high-throughput quantum dot labeled actin in vitro motility assay (Qdot assay) measures motor step-size in the context of an ensemble of actomyosin interactions. The ensemble context imposes a constant velocity constraint for myosins interacting with one actin filament. In a cardiac myosin producing multiple step-sizes, a "second characterization" is step-frequency that adjusts longer step-size to lower frequency maintaining a linear actin velocity identical to that from a shorter step-size and higher frequency actomyosin cycle. The step-frequency characteristic involves and integrates myosin enzyme kinetics, mechanical strain, and other ensemble affected characteristics. The high-throughput Qdot assay suits a new paradigm calling for wide surveillance of the vast number of disease or aging relevant myosin isoforms that contrasts with the alternative model calling for exhaustive research on a tiny subset myosin forms. The zebrafish embryo assay (Z assay) performs single myosin step-size and step-frequency assaying in vivo combining single myosin mechanical and whole muscle physiological characterizations in one model organism. The Qdot and Z assays cover "bottom-up" and "top-down" assaying of myosin characteristics.
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Affiliation(s)
- Thomas P Burghardt
- Department of Biochemistry and Molecular Biology, Mayo Clinic Rochester, Rochester, MN, 55905, USA.
- Department of Physiology and Biomedical Engineering, Mayo Clinic Rochester, Rochester, MN, 55905, USA.
| | - Xiaojing Sun
- Department of Biochemistry and Molecular Biology, Mayo Clinic Rochester, Rochester, MN, 55905, USA
| | - Yihua Wang
- Department of Biochemistry and Molecular Biology, Mayo Clinic Rochester, Rochester, MN, 55905, USA
| | - Katalin Ajtai
- Department of Biochemistry and Molecular Biology, Mayo Clinic Rochester, Rochester, MN, 55905, USA
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Wang Y, Ajtai K, Burghardt TP. Analytical comparison of natural and pharmaceutical ventricular myosin activators. Biochemistry 2014; 53:5298-306. [PMID: 25068717 PMCID: PMC4139156 DOI: 10.1021/bi500730t] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
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Ventricular myosin (βMys) is
the motor protein in cardiac
muscle generating force using ATP hydrolysis free energy to translate
actin. In the cardiac muscle sarcomere, myosin and actin filaments
interact cyclically and undergo rapid relative translation facilitated
by the low duty cycle motor. It contrasts with high duty cycle processive
myosins for which persistent actin association is the priority. The
only pharmaceutical βMys activator, omecamtive mecarbil (OM),
upregulates cardiac contractility in vivo and is
undergoing testing for heart failure therapy. In vitro βMys step-size, motility velocity, and actin-activated myosin
ATPase were measured to determine duty cycle in the absence and presence
of OM. A new parameter, the relative step-frequency, was introduced
and measured to characterize βMys motility due to the involvement
of its three unitary step-sizes. Step-size and relative step-frequency
were measured using the Qdot assay. OM decreases motility velocity
10-fold without affecting step-size, indicating a large increase in
duty cycle converting βMys to a near processive myosin. The
OM conversion dramatically increases force and modestly increases
power over the native βMys. Contrasting motility modification
due to OM with that from the natural myosin activator, specific βMys
phosphorylation, provides insight into their respective activation
mechanisms and indicates the boilerplate screening characteristics
desired for pharmaceutical βMys activators. New analytics introduced
here for the fast and efficient Qdot motility assay create a promising
method for high-throughput screening of motor proteins and their modulators.
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Affiliation(s)
- Yihua Wang
- Department of Biochemistry and Molecular Biology and ‡Department of Physiology and Biomedical Engineering, Mayo Clinic Rochester , Rochester, Minnesota 55905, United States
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Wang Y, Ajtai K, Burghardt TP. Ventricular myosin modifies in vitro step-size when phosphorylated. J Mol Cell Cardiol 2014; 72:231-7. [PMID: 24726887 PMCID: PMC4037356 DOI: 10.1016/j.yjmcc.2014.03.022] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/29/2014] [Revised: 03/11/2014] [Accepted: 03/31/2014] [Indexed: 10/25/2022]
Abstract
Cardiac and skeletal muscle myosins have the central role in contraction transducing ATP free energy into the mechanical work of moving actin. Myosin has a motor domain containing ATP and actin binding sites and a lever-arm that undergoes rotation impelling bound actin. The lever-arm converts torque generated in the motor into the linear displacement known as step-size. The myosin lever-arm is stabilized by bound essential and regulatory light chains (ELC and RLC). RLC phosphorylation at S15 is linked to modified lever-arm mechanical characteristics contributing to myosin filament based contraction regulation and to the response of the muscle to disease. Myosin step-size was measured using a novel quantum dot (Qdot) assay that previously confirmed a 5nm step-size for fast skeletal myosin and multiple unitary steps, most frequently 5 and 8nm, and a rare 3nm displacement for β cardiac myosin (βMys). S15 phosphorylation in βMys is now shown to change step-size distribution by advancing the 8nm step frequency. After phosphorylation, the 8nm step is the dominant myosin step-size resulting in significant gain in the average step-size. An increase in myosin step-size will increase the amount of work produced per ATPase cycle. The results indicate that RLC phosphorylation modulates work production per ATPase cycle suggesting the mechanism for contraction regulation by the myosin filament.
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Affiliation(s)
- Yihua Wang
- Department of Biochemistry and Molecular Biology, United States
| | - Katalin Ajtai
- Department of Biochemistry and Molecular Biology, United States
| | - Thomas P Burghardt
- Department of Biochemistry and Molecular Biology, United States; Department of Physiology and Biomedical Engineering, United States.
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Wang Y, Ajtai K, Burghardt TP. The Qdot-labeled actin super-resolution motility assay measures low-duty cycle muscle myosin step size. Biochemistry 2013; 52:1611-21. [PMID: 23383646 DOI: 10.1021/bi301702p] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Myosin powers contraction in heart and skeletal muscle and is a leading target for mutations implicated in inheritable muscle diseases. During contraction, myosin transduces ATP free energy into the work of muscle shortening against resisting force. Muscle shortening involves relative sliding of myosin and actin filaments. Skeletal actin filaments were fluorescently labeled with a streptavidin conjugate quantum dot (Qdot) binding biotin-phalloidin on actin. Single Qdots were imaged in time with total internal reflection fluorescence microscopy and then spatially localized to 1-3 nm using a super-resolution algorithm as they translated with actin over a surface coated with skeletal heavy meromyosin (sHMM) or full-length β-cardiac myosin (MYH7). The average Qdot-actin velocity matches measurements with rhodamine-phalloidin-labeled actin. The sHMM Qdot-actin velocity histogram contains low-velocity events corresponding to actin translation in quantized steps of ~5 nm. The MYH7 velocity histogram has quantized steps at 3 and 8 nm in addition to 5 nm and larger compliance compared to that of sHMM depending on the MYH7 surface concentration. Low-duty cycle skeletal and cardiac myosin present challenges for a single-molecule assay because actomyosin dissociates quickly and the freely moving element diffuses away. The in vitro motility assay has modestly more actomyosin interactions, and methylcellulose inhibited diffusion to sustain the complex while preserving a subset of encounters that do not overlap in time on a single actin filament. A single myosin step is isolated in time and space and then characterized using super-resolution. The approach provides a quick, quantitative, and inexpensive step size measurement for low-duty cycle muscle myosin.
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Affiliation(s)
- Yihua Wang
- Department of Biochemistry and Molecular Biology, Mayo Clinic Rochester, Rochester, Minnesota 55905, USA
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Josephson MP, Sikkink LA, Penheiter AR, Burghardt TP, Ajtai K. Smooth muscle myosin light chain kinase efficiently phosphorylates serine 15 of cardiac myosin regulatory light chain. Biochem Biophys Res Commun 2011; 416:367-71. [PMID: 22120626 DOI: 10.1016/j.bbrc.2011.11.044] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2011] [Accepted: 11/10/2011] [Indexed: 10/15/2022]
Abstract
Specific phosphorylation of the human ventricular cardiac myosin regulatory light chain (MYL2) modifies the protein at S15. This modification affects MYL2 secondary structure and modulates the Ca(2+) sensitivity of contraction in cardiac tissue. Smooth muscle myosin light chain kinase (smMLCK) is a ubiquitous kinase prevalent in uterus and present in other contracting tissues including cardiac muscle. The recombinant 130 kDa (short) smMLCK phosphorylated S15 in MYL2 in vitro. Specific modification of S15 was verified using the direct detection of the phospho group on S15 with mass spectrometry. SmMLCK also specifically phosphorylated myosin regulatory light chain S15 in porcine ventricular myosin and chicken gizzard smooth muscle myosin (S20 in smooth muscle) but failed to phosphorylate the myosin regulatory light chain in rabbit skeletal myosin. Phosphorylation kinetics, measured using a novel fluorescence method eliminating the use of radioactive isotopes, indicates similar Michaelis-Menten V(max) and K(M) for regulatory light chain S15 phosphorylation rates in MYL2, porcine ventricular myosin, and chicken gizzard myosin. These data demonstrate that smMLCK is a specific and efficient kinase for the in vitro phosphorylation of MYL2, cardiac, and smooth muscle myosin. Whether smMLCK plays a role in cardiac muscle regulation or response to a disease causing stimulus is unclear but it should be considered a potentially significant kinase in cardiac tissue on the basis of its specificity, kinetics, and tissue expression.
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Affiliation(s)
- Matthew P Josephson
- Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, MN 55905, USA
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Burghardt TP, Neff KL, Wieben ED, Ajtai K. Myosin individualized: single nucleotide polymorphisms in energy transduction. BMC Genomics 2010; 11:172. [PMID: 20226094 PMCID: PMC2848645 DOI: 10.1186/1471-2164-11-172] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2009] [Accepted: 03/15/2010] [Indexed: 11/28/2022] Open
Abstract
BACKGROUND Myosin performs ATP free energy transduction into mechanical work in the motor domain of the myosin heavy chain (MHC). Energy transduction is the definitive systemic feature of the myosin motor performed by coordinating in a time ordered sequence: ATP hydrolysis at the active site, actin affinity modulation at the actin binding site, and the lever-arm rotation of the power stroke. These functions are carried out by several conserved sub-domains within the motor domain. Single nucleotide polymorphisms (SNPs) affect the MHC sequence of many isoforms expressed in striated muscle, smooth muscle, and non-muscle tissue. The purpose of this work is to provide a rationale for using SNPs as a functional genomics tool to investigate structurefunction relationships in myosin. In particular, to discover SNP distribution over the conserved sub-domains and surmise what it implies about sub-domain stability and criticality in the energy transduction mechanism. RESULTS An automated routine identifying human nonsynonymous SNP amino acid missense substitutions for any MHC gene mined the NCBI SNP data base. The routine tested 22 MHC genes coding muscle and non-muscle isoforms and identified 89 missense mutation positions in the motor domain with 10 already implicated in heart disease and another 8 lacking sequence homology with a skeletal MHC isoform for which a crystallographic model is available. The remaining 71 SNP substitutions were found to be distributed over MHC with 22 falling outside identified functional sub-domains and 49 in or very near to myosin sub-domains assigned specific crucial functions in energy transduction. The latter includes the active site, the actin binding site, the rigid lever-arm, and regions facilitating their communication. Most MHC isoforms contained SNPs somewhere in the motor domain. CONCLUSIONS Several functional-crucial sub-domains are infiltrated by a large number of SNP substitution sites suggesting these domains are engineered by evolution to be too-robust to be disturbed by otherwise intrusive sequence changes. Two functional sub-domains are SNP-free or relatively SNP-deficient but contain many disease implicated mutants. These sub-domains are apparently highly sensitive to any missense substitution suggesting they have failed to evolve a robust sequence paradigm for performing their function.
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Affiliation(s)
- Thomas P Burghardt
- Department of Biochemistry and Molecular Biology, Mayo Clinic Rochester, 200 First Street SW, Rochester, MN 55905, USA
- Department of Physiology and Biomedical Engineering, Mayo Clinic Rochester, 200 First Street SW, Rochester, MN 55905, USA
| | - Kevin L Neff
- Department of Biochemistry and Molecular Biology, Mayo Clinic Rochester, 200 First Street SW, Rochester, MN 55905, USA
| | - Eric D Wieben
- Department of Biochemistry and Molecular Biology, Mayo Clinic Rochester, 200 First Street SW, Rochester, MN 55905, USA
| | - Katalin Ajtai
- Department of Biochemistry and Molecular Biology, Mayo Clinic Rochester, 200 First Street SW, Rochester, MN 55905, USA
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Ajtai K, Halstead MF, Nyitrai M, Penheiter AR, Zheng Y, Burghardt TP. The myosin C-loop is an allosteric actin contact sensor in actomyosin. Biochemistry 2009; 48:5263-75. [PMID: 19408946 PMCID: PMC2759872 DOI: 10.1021/bi900584q] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Actin and myosin form the molecular motor in muscle. Myosin is the enzyme performing ATP hydrolysis under the allosteric control of actin such that actin binding initiates product release and force generation in the myosin power stroke. Non-equilibrium Monte Carlo molecular dynamics simulation of the power stroke suggested that a structured surface loop on myosin, the C-loop, is the actin contact sensor initiating actin activation of the myosin ATPase. Previous experimental work demonstrated C-loop binds actin and established the forward and reverse allosteric link between the C-loop and the myosin active site. Here, smooth muscle heavy meromyosin C-loop chimeras were constructed with skeletal (sCl) and cardiac (cCl) myosin C-loops substituted for the native sequence. In both cases, actin-activated ATPase inhibition is indicated mainly by the lower V(max). In vitro motility was also inhibited in the chimeras. Motility data were collected as a function of myosin surface density, with unregulated actin, and with skeletal and cardiac isoforms of tropomyosin-bound actin for the wild type, cCl, and sCl. Slow and fast subpopulations of myosin velocities in the wild-type species were discovered and represent geometrically unfavorable and favorable actomyosin interactions, respectively. Unfavorable interactions are detected at all surface densities tested. Favorable interactions are more probable at higher myosin surface densities. Cardiac tropomyosin-bound actin promotes the favorable actomyosin interactions by lowering the inhibiting geometrical constraint barriers with a structural effect on actin. Neither higher surface density nor cardiac tropomyosin-bound actin can accelerate motility velocity in cCl or sCl, suggesting the element initiating maximal myosin activation by actin resides in the C-loop.
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Affiliation(s)
- Katalin Ajtai
- Biochemistry and Molecular Biology, Mayo Clinic College of Medicine, Rochester, Minnesota 55905
| | - Miriam F. Halstead
- Biochemistry and Molecular Biology, Mayo Clinic College of Medicine, Rochester, Minnesota 55905
| | - Miklós Nyitrai
- Department of Biophysics, University of Pécs, Pécs, Hungary
| | - Alan R. Penheiter
- Molecular Medicine Program, Mayo Clinic College of Medicine, Rochester, Minnesota 55905
| | - Ye Zheng
- Biochemistry and Molecular Biology, Mayo Clinic College of Medicine, Rochester, Minnesota 55905
| | - Thomas P. Burghardt
- Biochemistry and Molecular Biology, Mayo Clinic College of Medicine, Rochester, Minnesota 55905
- Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, Minnesota 55905
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Higashi-Fujime S, Nakamura A. Cell and molecular biology of the fastest myosins. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2009; 276:301-47. [PMID: 19584016 DOI: 10.1016/s1937-6448(09)76007-1] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Chara myosin is a class XI plant myosin in green algae Chara corallina and responsible for fast cytoplasmic streaming. The Chara myosin exhibits the fastest sliding movement of F-actin at 60 mum/s as observed so far, 10-fold of the shortening speed of muscle. It has some distinct properties differing from those of muscle myosin. Although knowledge about Chara myosin is very limited at present, we have tried to elucidate functional bases of its characteristics by comparing with those of other myosins. In particular, we have built the putative atomic model of Chara myosin by using the homology-based modeling system and databases. Based on the putative structure of Chara myosin obtained, we have analyzed the relationship between structure and function of Chara myosin to understand its distinct properties from various aspects by referring to the accumulated knowledge on mechanochemical and structural properties of other classes of myosin, particularly animal and fungal myosin V. We will also discuss the functional significance of Chara myosin in a living cell.
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Affiliation(s)
- Sugie Higashi-Fujime
- Department of Molecular and Cellular Pharmacology, Gunma University Graduate School of Medicine, Maebashi, Gunma, Japan
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13
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Halstead MF, Ajtai K, Penheiter AR, Spencer JD, Zheng Y, Morrison EA, Burghardt TP. An unusual transduction pathway in human tonic smooth muscle myosin. Biophys J 2007; 93:3555-66. [PMID: 17704147 PMCID: PMC2072059 DOI: 10.1529/biophysj.106.100818] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The motor protein myosin binds actin and ATP, producing work by causing relative translation of the proteins while transducing ATP free energy. Smooth muscle myosin has one of four heavy chains encoded by the MYH11 gene that differ at the C-terminus and in the active site for ATPase due to alternate splicing. A seven-amino-acid active site insert in phasic muscle myosin is absent from the tonic isoform. Fluorescence increase in the nucleotide sensitive tryptophan (NST) accompanies nucleotide binding and hydrolysis in several myosin isoforms implying it results from a common origin within the motor. A wild-type tonic myosin (smA) construct of the enzymatic head domain (subfragment 1 or S1) has seven tryptophan residues and nucleotide-induced fluorescence enhancement like other myosins. Three smA mutants probe the molecular basis for the fluorescence enhancement. W506+ contains one tryptophan at position 506 homologous to the NST in other myosins. W506F has the native tryptophans except phenylalanine replaces W506, and W506+(Y499F) is W506+ with phenylalanine replacing Y499. W506+ lacks nucleotide-induced fluorescence enhancement probably eliminating W506 as the NST. W506F has impaired ATPase activity but retains nucleotide-induced fluorescence enhancement. Y499F replacement in W506+ partially rescues nucleotide sensitivity demonstrating the role of Y499 as an NST facilitator. The exceptional response of W506 to active site conformation opens the possibility that phasic and tonic isoforms differ in how influences from active site ATPase propagate through the protein network.
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Affiliation(s)
- Miriam F Halstead
- Biochemistry and Molecular Biology, Mayo Clinic College of Medicine, Rochester, Minnesota, USA
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Liu Y, Scolari M, Im W, Woo HJ. Protein-protein interactions in actin-myosin binding and structural effects of R405Q mutation: a molecular dynamics study. Proteins 2006; 64:156-66. [PMID: 16645962 DOI: 10.1002/prot.20993] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Detailed residue-wise interactions involved in the binding of myosin to actin in the rigor conformation without nucleotides have been examined using molecular dynamics simulations of the chicken skeletal myosin head complexed with two actin monomers, based on the cryo-microscopic model of Holmes et al. (Nature 2003;425:423-427). The overall interaction is largely electrostatic in nature, because of the charged residues in the four loops surrounding the central primary binding site. The 50k/20k loop, disordered in crystal structures and in simulations of free myosin in solution, was found to be in a conformation stabilized with 1 - 2 internal salt bridges. The cardiomyopathy loop forms 2 - 3 interprotein salt bridges with actin monomers upon binding, whereas its Arg405 residue, the mutation site associated with the hypertrophic cardiomyopathy, forms a strong salt bridge with Glu605 in the neighboring helix away from actin in the actin-bound myosin. The myopathy loop of the R405Q mutant maintains a high degree of two-strand beta-sheet character when bound to actin with the corresponding salt bridges broken.
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Affiliation(s)
- Yuemin Liu
- Department of Chemistry, University of Nevada, Reno 89557, USA
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Ajtai K, Garamszegi SP, Watanabe S, Ikebe M, Burghardt TP. The myosin cardiac loop participates functionally in the actomyosin interaction. J Biol Chem 2004; 279:23415-21. [PMID: 15020589 DOI: 10.1074/jbc.m310775200] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The motor protein myosin in association with actin transduces chemical free energy in ATP into work in the form of actin translation against an opposing force. Mediating the actomyosin interaction in myosin is an actin binding site distributed among several peptides on the myosin surface including surface loops contributing to affinity and actin regulation of myosin ATPase. A structured surface loop on beta-cardiac myosin, the cardiac or C-loop, was recently demonstrated to affect myosin ATPase and was indirectly implicated in the actomyosin interaction. The C-loop is a conserved feature of all myosin isoforms with crystal structures, suggesting that it is an essential part of the core energy transduction machinery. It is shown here that proteolytic digestion of the C-loop in beta-cardiac myosin eliminates actin-activated myosin ATPase and reduces actomyosin affinity in rigor more than 100-fold. Studies of C-loop function in smooth muscle myosin were also undertaken using site-directed mutagenesis. Mutagenesis of a single charged residue in the C-loop of smooth muscle myosin alters actomyosin affinity and doubles myosin in vitro motility and actin-activated ATPase velocities, thereby involving a charged region of the loop in the actomyosin interaction. It appears likely that the C-loop is an essential electrostatic binding site for actin involved in modulation of actomyosin affinity and regulation of actomyosin ATPase velocity.
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Affiliation(s)
- Katalin Ajtai
- Department of Biochemistry and Molecular Biology, Mayo Clinic Rochester, Rochester, Minnesota 55905, USA
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The Chemistry of Movement. Biochemistry 2001. [DOI: 10.1016/b978-012492543-4/50022-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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