title: Load-dependent kinetics of myosin-V can explain its high processivity.
abstract: Recent studies provide strong evidence that single myosin class V molecules transport vesicles and organelles processively along F-actin, taking several 36-nm steps, 'hand over hand', for each diffusional encounter. The mechanisms regulating myosin-V's processivity remain unknown. Here, we have used an optical-tweezers-based transducer to measure the effect of load on the mechanical interactions between rabbit skeletal F-actin and a single head of mouse brain myosin-V, which produces its working stroke in two phases. We found that the lifetimes of the first phase of the working stroke changed exponentially and about 10-fold over a range of pushing and pulling forces of +/- 1.5 pN. Stiffness measurements suggest that intramolecular forces could approach 3.6 pN when both heads are bound to F-actin, in which case extrapolation would predict the detachment kinetics of the front head to slow down 50-fold and the kinetics of the rear head to accelerate respectively. This synchronizing effect on the chemo-mechanical cycles of the heads increases the probability of the trail head detaching first and causes a strong increase in the number of forward steps per diffusional encounter over a system with no strain dependence.
authors.affiliation: Physical Biochemistry, National Institute for Medical Research, The Ridgeway, Mill Hill, London NW7 1AA, UK. cveigel@nimr.mrc.ac.uk
authors.forename: Claudia
authors.initials: C
authors.lastname: Veigel
authors.forename: Stephan
authors.initials: S
authors.lastname: Schmitz
authors.forename: Fei
authors.initials: F
authors.lastname: Wang
authors.forename: James R
authors.initials: JR
authors.lastname: Sellers
mesh_terms: D000199:Actins / Q000737:chemistry / Q000378:metabolism*; D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001665:Binding Sites / Q000502:physiology; D001696:Biomechanical Phenomena; D002645:Chickens; D051379:Mice; D008958:Models, Molecular; D020409:Molecular Motor Proteins / Q000737:chemistry / Q000378:metabolism*; D024701:Myosin Type V / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding / Q000502:physiology; D017433:Protein Structure, Secondary / Q000502:physiology; D021381:Protein Transport / Q000502:physiology; D011817:Rabbits; D013314:Stress, Mechanical; D016474:Weight-Bearing / Q000502:physiology
chemical_list: D000199:Actins; D020409:Molecular Motor Proteins; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D024701:Myosin Type V