title: Orientation changes of the myosin light chain domain during filament sliding in active and rigor muscle.
abstract: Structural changes in myosin power many types of cell motility including muscle contraction. Tilting of the myosin light chain domain (LCD) seems to be the final step in transducing the energy of ATP hydrolysis, amplifying small structural changes near the ATP binding site into nanometer-scale motions of the filaments. Here we used polarized fluorescence measurements from bifunctional rhodamine probes attached at known orientations in the LCD to describe the distribution of orientations of the LCD in active contraction and rigor. We applied rapid length steps to perturb the orientations of the population of myosin heads that are attached to actin, and thereby characterized the motions of these force-bearing myosin heads. During active contraction, this population is a small fraction of the total. When the filaments slide in the shortening direction in active contraction, the long axis of LCD tilts towards its nucleotide-free orientation with no significant twisting around this axis. In contrast, filament sliding in rigor produces coordinated tilting and twisting motions.
authors.affiliation: Pennsylvania Muscle Institute, University of Pennsylvania, Philadelphia 19104-6083, USA.
authors.forename: Seth C
authors.initials: SC
authors.lastname: Hopkins
authors.forename: Cibele
authors.initials: C
authors.lastname: Sabido-David
authors.forename: Uulke A
authors.initials: UA
authors.lastname: van der Heide
authors.forename: Roisean E
authors.initials: RE
authors.lastname: Ferguson
authors.forename: Birgit D
authors.initials: BD
authors.lastname: Brandmeier
authors.forename: Robert E
authors.initials: RE
authors.lastname: Dale
authors.forename: John
authors.initials: J
authors.lastname: Kendrick-Jones
authors.forename: John E T
authors.initials: JE
authors.lastname: Corrie
authors.forename: David R
authors.initials: DR
authors.lastname: Trentham
authors.forename: Malcolm
authors.initials: M
authors.lastname: Irving
authors.forename: Yale E
authors.initials: YE
authors.lastname: Goldman
mesh_terms: D000818:Animals; D002645:Chickens; D003545:Cysteine; D005454:Fluorescence Polarization; D020409:Molecular Motor Proteins / Q000737:chemistry*; D009119:Muscle Contraction; D018485:Muscle Fibers, Skeletal / Q000737:chemistry* / Q000502:physiology; D018994:Myosin Light Chains / Q000737:chemistry* / Q000502:physiology; D017434:Protein Structure, Tertiary
chemical_list: D020409:Molecular Motor Proteins; D018994:Myosin Light Chains; D003545:Cysteine