- On the Functional Assessment of Hypertrophic Cardiomyopathy-Causing Mutations in Human beta-Cardiac Myosin and the Role of Myosin Binding Protein-C CELL PRESS. 2019: 466A?467A
Converter domain mutations in myosin alter structural kinetics and motor function.
The Journal of biological chemistry
Myosins are molecular motors that use a conserved ATPase cycle to generate force. We investigated two mutations in the converter domain of myosin V (R712G and F750L) to examine how altering specific structural transitions in the motor ATPase cycle can impair myosin mechanochemistry. The corresponding mutations in the human beta-cardiac myosin gene are associated with hypertrophic and dilated cardiomyopathy, respectively. Despite similar steady-state actin-activated ATPase and unloaded in vitro motility sliding velocities, both R712G and F750L were less able to overcome frictional loads measured in the loaded motility assay. Transient kinetic analysis and stopped-flow FRET demonstrated that the R712G mutation slowed the maximum ATP hydrolysis and recovery stroke rate constants, while the F750L mutation enhanced these steps. In both mutants, the fast and slow power stroke as well as actin-activated phosphate release rate constants were not significantly different from WT. Time-resolved FRET experiments revealed that R712G and F750L populate the pre- and post-power stroke states with similar FRET distance and distance distribution profiles. The R712G mutant increased the mole fraction in the post-power stroke conformation in the strong actin binding states, while the F750L decreased this population in the actomyosin ADP state. We conclude that mutations in key allosteric pathways can shift the equilibrium and/or alter the activation energy associated with key structural transitions without altering the overall conformation of the pre- and post-power stroke states. Thus, therapies designed to alter the transition between structural states may be able to rescue the impaired motor function induced by disease mutations.
View details for DOI 10.1074/jbc.RA118.006128
View details for PubMedID 30518549
Impact of Hypertrophic Cardiomyopathy Mutations and the Role of Myosin Binding Protein-C on the Sequestered State of Myosin
CELL PRESS. 2018: 317A
View details for Web of Science ID 000430450000089
Hypertrophic Cardiomyopathy Mutations Disrupt Human Beta Cardiac Myosin Intramolecular Interactions Leading to Increased Myosin Activity
CELL PRESS. 2018: 139A
View details for Web of Science ID 000429315800699
A Molecular Approach to Understand the Super-Relaxed State of Myosin Observed in Cardiac Muscle
CELL PRESS. 2018: 141A
View details for Web of Science ID 000429315800710
SETD3 is an actin histidine methyltransferase that prevents primary dystocia.
For more than 50 years, the methylation of mammalian actin at histidine 73 has been known to occur1. Despite the pervasiveness of His73 methylation, which we find is conserved in several model animals and plants, its function remains unclear and the enzyme that generates this modification is unknown. Here we identify SET domain protein 3 (SETD3) as the physiological actin His73 methyltransferase. Structural studies reveal that an extensive network of interactions clamps the actin peptide onto the surface of SETD3 to orient His73 correctly within the catalytic pocket and to facilitate methyl transfer. His73 methylation reduces the nucleotide-exchange rate on actin monomers and modestly accelerates the assembly of actin filaments. Mice that lack SETD3 show complete loss of actin His73 methylation in several tissues, and quantitative proteomics analysis shows that actin His73 methylation is the only detectable physiological substrate of SETD3. SETD3-deficient female mice have severely decreased litter sizes owing to primary maternal dystocia that is refractory to ecbolic induction agents. Furthermore, depletion of SETD3 impairs signal-induced contraction in primary human uterine smooth muscle cells. Together, our results identify a mammalian histidine methyltransferase and uncover a pivotal role for SETD3 and actin His73 methylation in the regulation of smooth muscle contractility. Our data also support the broader hypothesis that protein histidine methylation acts as a common regulatory mechanism.
View details for PubMedID 30626964
- Investigation of the Molecular Interactions Regulating the Function of Human Cardiac Myosin CELL PRESS. 2017: 259A
- Uncovering the Molecular Interactions that Maintain the Sequestered State of Myosin and their Implication in Hypertrophic Cardiomyopathy CELL PRESS. 2017: 164A
Hypertrophic cardiomyopathy and the myosin mesa: viewing an old disease in a new light.
The sarcomere is an exquisitely designed apparatus that is capable of generating force, which in the case of the heart results in the pumping of blood throughout the body. At the molecular level, an ATP-dependent interaction of myosin with actin drives the contraction and force generation of the sarcomere. Over the past six decades, work on muscle has yielded tremendous insights into the workings of the sarcomeric system. We now stand on the cusp where the acquired knowledge of how the sarcomere contracts and how that contraction is regulated can be extended to an understanding of the molecular mechanisms of sarcomeric diseases, such as hypertrophic cardiomyopathy (HCM). In this review we present a picture that combines current knowledge of the myosin mesa, the sequestered state of myosin heads on the thick filament, known as the interacting-heads motif (IHM), their possible interaction with myosin binding protein C (MyBP-C) and how these interactions can be abrogated leading to hyper-contractility, a key clinical manifestation of HCM. We discuss the structural and functional basis of the IHM state of the myosin heads and identify HCM-causing mutations that can directly impact the equilibrium between the 'on state' of the myosin heads (the open state) and the IHM 'off state'. We also hypothesize a role of MyBP-C in helping to maintain myosin heads in the IHM state on the thick filament, allowing release in a graded manner upon adrenergic stimulation. By viewing clinical hyper-contractility as the result of the destabilization of the IHM state, our aim is to view an old disease in a new light.
View details for PubMedID 28717924
- On the Molecular Basis of Monogenic Human Hypertrophic and Dilated Cardiomyopathies CELL PRESS. 2016: 8A
Effects of hypertrophic and dilated cardiomyopathy mutations on power output by human beta-cardiac myosin
JOURNAL OF EXPERIMENTAL BIOLOGY
2016; 219 (2): 161-167
Hypertrophic cardiomyopathy is the most frequently occurring inherited cardiovascular disease, with a prevalence of more than one in 500 individuals worldwide. Genetically acquired dilated cardiomyopathy is a related disease that is less prevalent. Both are caused by mutations in the genes encoding the fundamental force-generating protein machinery of the cardiac muscle sarcomere, including human ?-cardiac myosin, the motor protein that powers ventricular contraction. Despite numerous studies, most performed with non-human or non-cardiac myosin, there is no clear consensus about the mechanism of action of these mutations on the function of human ?-cardiac myosin. We are using a recombinantly expressed human ?-cardiac myosin motor domain along with conventional and new methodologies to characterize the forces and velocities of the mutant myosins compared with wild type. Our studies are extending beyond myosin interactions with pure actin filaments to include the interaction of myosin with regulated actin filaments containing tropomyosin and troponin, the roles of regulatory light chain phosphorylation on the functions of the system, and the possible roles of myosin binding protein-C and titin, important regulatory components of both cardiac and skeletal muscles.
View details for DOI 10.1242/jeb.125930
View details for Web of Science ID 000368546300006
Direct measurements of the coordination of lever arm swing and the catalytic cycle in myosin V
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2015; 112 (47): 14593-14598
Myosins use a conserved structural mechanism to convert the energy from ATP hydrolysis into a large swing of the force-generating lever arm. The precise timing of the lever arm movement with respect to the steps in the actomyosin ATPase cycle has not been determined. We have developed a FRET system in myosin V that uses three donor-acceptor pairs to examine the kinetics of lever arm swing during the recovery and power stroke phases of the ATPase cycle. During the recovery stroke the lever arm swing is tightly coupled to priming the active site for ATP hydrolysis. The lever arm swing during the power stroke occurs in two steps, a fast step that occurs before phosphate release and a slow step that occurs before ADP release. Time-resolved FRET demonstrates a 20-Å change in distance between the pre- and postpower stroke states and shows that the lever arm is more dynamic in the postpower stroke state. Our results suggest myosin binding to actin in the ADP.Pi complex triggers a rapid power stroke that gates the release of phosphate, whereas a second slower power stroke may be important for mediating strain sensitivity.
View details for DOI 10.1073/pnas.1517566112
View details for Web of Science ID 000365173100062
View details for PubMedID 26553992
Magnesium Modulates Actin Binding and ADP Release in Myosin Motors
JOURNAL OF BIOLOGICAL CHEMISTRY
2014; 289 (34): 23977-23991
We examined the magnesium dependence of five class II myosins, including fast skeletal muscle myosin, smooth muscle myosin, ?-cardiac myosin (CMIIB), Dictyostelium myosin II (DdMII), and nonmuscle myosin IIA, as well as myosin V. We found that the myosins examined are inhibited in a Mg(2+)-dependent manner (0.3-9.0 mm free Mg(2+)) in both ATPase and motility assays, under conditions in which the ionic strength was held constant. We found that the ADP release rate constant is reduced by Mg(2+) in myosin V, smooth muscle myosin, nonmuscle myosin IIA, CMIIB, and DdMII, although the ADP affinity is fairly insensitive to Mg(2+) in fast skeletal muscle myosin, CMIIB, and DdMII. Single tryptophan probes in the switch I (Trp-239) and switch II (Trp-501) region of DdMII demonstrate these conserved regions of the active site are sensitive to Mg(2+) coordination. Cardiac muscle fiber mechanic studies demonstrate cross-bridge attachment time is increased at higher Mg(2+) concentrations, demonstrating that the ADP release rate constant is slowed by Mg(2+) in the context of an activated muscle fiber. Direct measurements of phosphate release in myosin V demonstrate that Mg(2+) reduces actin affinity in the M·ADP·Pi state, although it does not change the rate of phosphate release. Therefore, the Mg(2+) inhibition of the actin-activated ATPase activity observed in class II myosins is likely the result of Mg(2+)-dependent alterations in actin binding. Overall, our results suggest that Mg(2+) reduces the ADP release rate constant and rate of attachment to actin in both high and low duty ratio myosins.
View details for DOI 10.1074/jbc.M114.562231
View details for Web of Science ID 000341505000062
View details for PubMedID 25006251
Magnesium Impacts Myosin V Motor Activity by Altering Key Conformational Changes in the Mechanochemical Cycle
2013; 52 (27): 4710-4722
We investigated how magnesium (Mg) impacts key conformational changes during the ADP binding/release steps in myosin V and how these alterations impact the actomyosin mechanochemical cycle. The conformation of the nucleotide binding pocket was examined with our established FRET system in which myosin V labeled with FlAsH in the upper 50 kDa domain participates in energy transfer with mant labeled nucleotides. We examined the maximum actin-activated ATPase activity of MV FlAsH at a range of free Mg concentrations (0.1-9 mM) and found that the highest activity occurs at low Mg (0.1-0.3 mM), while there is a 50-60% reduction in activity at high Mg (3-9 mM). The motor activity examined with the in vitro motility assay followed a similar Mg-dependence, and the trend was similar with dimeric myosin V. Transient kinetic FRET studies of mantdADP binding/release from actomyosin V FlAsH demonstrate that the transition between the weak and strong actomyosin.ADP states is coupled to movement of the upper 50 kDa domain and is dependent on Mg with the strong state stabilized by Mg. We find that the kinetics of the upper 50 kDa conformational change monitored by FRET correlates well with the ATPase and motility results over a wide range of Mg concentrations. Our results suggest the conformation of the upper 50 kDa domain is highly dynamic in the Mg free actomyosin.ADP state, which is in agreement with ADP binding being entropy driven in the absence of Mg. Overall, our results demonstrate that Mg is a key factor in coupling the nucleotide- and actin-binding regions. In addition, Mg concentrations in the physiological range can alter the structural transition that limits ADP dissociation from actomyosin V, which explains the impact of Mg on actin-activated ATPase activity and in vitro motility.
View details for DOI 10.1021/bi4004364
View details for Web of Science ID 000321793200013
View details for PubMedID 23725637
Switch II Mutants Reveal Coupling between the Nucleotide- and Actin-Binding Regions in Myosin V
2012; 102 (11): 2545-2555
Conserved active-site elements in myosins and other P-loop NTPases play critical roles in nucleotide binding and hydrolysis; however, the mechanisms of allosteric communication among these mechanoenzymes remain unresolved. In this work we introduced the E442A mutation, which abrogates a salt-bridge between switch I and switch II, and the G440A mutation, which abolishes a main-chain hydrogen bond associated with the interaction of switch II with the ? phosphate of ATP, into myosin V. We used fluorescence resonance energy transfer between mant-labeled nucleotides or IAEDANS-labeled actin and FlAsH-labeled myosin V to examine the conformation of the nucleotide- and actin-binding regions, respectively. We demonstrate that in the absence of actin, both the G440A and E442A mutants bind ATP with similar affinity and result in only minor alterations in the conformation of the nucleotide-binding pocket (NBP). In the presence of ADP and actin, both switch II mutants disrupt the formation of a closed NBP actomyosin.ADP state. The G440A mutant also prevents ATP-induced opening of the actin-binding cleft. Our results indicate that the switch II region is critical for stabilizing the closed NBP conformation in the presence of actin, and is essential for communication between the active site and actin-binding region.
View details for DOI 10.1016/j.bpj.2012.04.025
View details for Web of Science ID 000305003100017
View details for PubMedID 22713570
Kinetics and Thermodynamics of the Rate-Limiting Conformational Change in the Actomyosin V Mechanochemical Cycle
JOURNAL OF MOLECULAR BIOLOGY
2011; 407 (5): 716-730
We used FRET to examine the kinetics and thermodynamics of structural changes associated with ADP release in myosin V, which is thought to be a strain-sensitive step in many muscle and non-muscle myosins. We also explored essential dynamics using FIRST/FRODA starting with three different myosin V X-ray crystal structures to examine intrinsic flexibility and correlated motions. Our steady-state and time-resolved FRET analysis demonstrates a temperature-dependent reversible conformational change in the nucleotide-binding pocket (NBP). Our kinetic results demonstrate that the NBP goes from a closed to an open conformation prior to the release of ADP, while the actin-binding cleft remains closed. Interestingly, we find that the temperature dependence of the maximum actin-activated myosin V ATPase rate is similar to the pocket opening step, demonstrating that this is the rate-limiting structural transition in the ATPase cycle. Thermodynamic analysis demonstrates that the transition from the open to closed NBP conformation is unfavorable because of a decrease in entropy. The intrinsic flexibility analysis is consistent with conformational entropy playing a role in this transition as the MV.ADP structure is highly flexible compared to the MV.APO structure. Our experimental and modeling studies support the conclusion of a novel post-power-stroke actomyosin.ADP state in which the NBP and actin-binding cleft are closed. The novel state may be important for strain sensitivity as the transition from the closed to open NBP conformation may be altered by lever arm position.
View details for DOI 10.1016/j.jmb.2011.02.001
View details for Web of Science ID 000289134000009
View details for PubMedID 21315083