Load-dependent kinetics and mechanics of single cardiac myosin molecules
Abstract/Contents
- Abstract
- Cardiomyopathy-causing mutations and small molecule drugs can alter contractility of the heart muscle. Here, I investigate the underlying mechanism at the level of individual molecules of human β-cardiac myosin, the isoform responsible for power production in the ventricles of the heart. I measured single myosin molecules' rate of detachment kdet(F) from actin and its load dependence by optical trapping. I find that the rate and its load dependence are modulated to various extents by (i) cardiac myosin-specific small molecule compounds, including omecamtiv mecarbil (OM), a drug in phase III clinical trials for treatment of heart failure, and (ii) mutations in myosin that cause hypertrophic (HCM: D239N, H251N) or dilated (DCM: A223T, R237W, S532P) cardiomyopathies. Furthermore, effects of mutations can be reversed by introducing appropriate compounds. The duty ratio, average force, and average power of single myosin molecules can be determined given kdet(F), and herein lies a striking separation between activating vs. inhibitory perturbations consistent with physiological expectations. Stated simply, hypo- and hyper-contractility are observed at the level of individual myosin molecules. I next investigate the load-dependent detachment kinetics of OM in greater detail to understand its mechanism to activate the heart. The drug dramatically slows myosin's detachment rate so that myosin stays bound to actin ~6x longer, from ~10 ms to ~60 ms. Single-molecule dosage analysis reveals two populations of events -- one fast in which the drug is not bound to myosin, and the other slow in which the drug is bound. The fraction of OM-bound events depends on the concentration of the drug. It is proposed that the prolonged attachment duration between myosin and actin in the presence of OM prolongs the activation of the thick and thin filaments in the sarcomere, thereby prolonging contraction as observed clinically. Finally, in addition to the load-dependent detachment rate kdet(F), another key parameter of cardiac contractility is myosin's stroke size. I present a novel analysis method which extracts stroke size information from data collected originally for determining kdet(F). Preliminary analyses show that stroke size is also modulated by mutations and small molecule compounds. Together, these investigations of myosin's load-dependent kinetics and stroke size provide an opportunity in molecular medicine to understand modulation of cardiac contractility from the level of individual myosin molecules.
Description
| Type of resource | text |
|---|---|
| Form | electronic resource; remote; computer; online resource |
| Extent | 1 online resource. |
| Place | California |
| Place | [Stanford, California] |
| Publisher | [Stanford University] |
| Copyright date | 2018; ©2018 |
| Publication date | 2018; 2018 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Author | Liu, Chao |
|---|---|
| Degree supervisor | Spudich, James A |
| Thesis advisor | Spudich, James A |
| Thesis advisor | Harbury, Pehr |
| Thesis advisor | Krasnow, Mark, 1956- |
| Degree committee member | Harbury, Pehr |
| Degree committee member | Krasnow, Mark, 1956- |
| Associated with | Stanford University, Department of Biochemistry. |
Subjects
| Genre | Theses |
|---|---|
| Genre | Text |
Bibliographic information
| Statement of responsibility | Chao Liu. |
|---|---|
| Note | Submitted to the Department of Biochemistry. |
| Thesis | Thesis Ph.D. Stanford University 2018. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2018 by Chao Liu
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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