title: N-Terminus of Cardiac Myosin Essential Light Chain Modulates Myosin Step-Size.
abstract: Muscle myosin cyclically hydrolyzes ATP to translate actin. Ventricular cardiac myosin (βmys) 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 βmys (Δ17βmys) and a 43 residue N-terminal truncated human vELC expressed in transgenic mouse heart (Δ43αmys). Step-size and step-frequency were measured using the Qdot motility assay. Both Δ17βmys and Δ43αmys 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.
authors.forename: Yihua
authors.initials: Y
authors.lastname: Wang
authors.forename: Katalin
authors.initials: K
authors.lastname: Ajtai
authors.affiliation: Department of Molecular and Cellular Pharmacology, University of Miami Miller School of Medicine , Miami, Florida 33136, United States.
authors.forename: Katarzyna
authors.initials: K
authors.lastname: Kazmierczak
authors.affiliation: Department of Molecular and Cellular Pharmacology, University of Miami Miller School of Medicine , Miami, Florida 33136, United States.
authors.forename: Danuta
authors.initials: D
authors.lastname: Szczesna-Cordary
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Burghardt
mesh_terms: D000199:Actins / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D024722:Cardiac Myosins / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D051379:Mice; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D009206:Myocardium / Q000737:chemistry / Q000378:metabolism*; D018994:Myosin Light Chains / Q000737:chemistry* / Q000378:metabolism*; D011487:Protein Conformation; D055503:Protein Multimerization; D013552:Swine
chemical_list: D000199:Actins; D018994:Myosin Light Chains; D024722:Cardiac Myosins