N-Terminus of Cardiac Myosin Essential Light Chain Modulates Myosin Step-Size.

ABSTRACT: Muscle myosin cyclically hydrolyzes ATP to translate actin. Ventricular cardiac myosin (?mys) moves actin with three distinct unitary step-sizes resulting from its lever-arm rotation and with step-frequencies that are modulated in a myosin regulation mechanism. The lever-arm associated essential light chain (vELC) binds actin by its 43 residue N-terminal extension. Unitary steps were proposed to involve the vELC N-terminal extension with the 8 nm step engaging the vELC/actin bond facilitating an extra ?19 degrees of lever-arm rotation while the predominant 5 nm step forgoes vELC/actin binding. A minor 3 nm step is the unlikely conversion of the completed 5 to the 8 nm step. This hypothesis was tested using a 17 residue N-terminal truncated vELC in porcine ?mys (?17?mys) and a 43 residue N-terminal truncated human vELC expressed in transgenic mouse heart (?43?mys). Step-size and step-frequency were measured using the Qdot motility assay. Both ?17?mys and ?43?mys had significantly increased 5 nm step-frequency and coincident loss in the 8 nm step-frequency compared to native proteins suggesting the vELC/actin interaction drives step-size preference. Step-size and step-frequency probability densities depend on the relative fraction of truncated vELC and relate linearly to pure myosin species concentrations in a mixture containing native vELC homodimer, two truncated vELCs in the modified homodimer, and one native and one truncated vELC in the heterodimer. Step-size and step-frequency, measured for native homodimer and at two or more known relative fractions of truncated vELC, are surmised for each pure species by using a new analytical method.

SUBMITTER: Wang Y 

PROVIDER: S-EPMC4727542 | biostudies-literature | 2016 Jan

REPOSITORIES: biostudies-literature