Mammalian class I myosin, Myo1b, is monomeric and cross-links actin filaments as determined by hydrodynamic studies and electron microscopy.
The class I myosin, Myo1b, is a calmodulin- and actin-associated molecular motor widely expressed in mammalian tissues. Analytical ultracentrifugation studies indicate that Myo1b purified from rat liver has a Stokes radius of 6.7 nm and a sedimentation coefficient, s(20,w), of 7.0 S with a predicted molar mass of 213 kg/mol. These results indicate that Myo1b is monomeric and consists primarily of a splice variant having five associated calmodulins. Molecular modeling based on the analytical ultracentrifugation studies are supported by electron microscopy studies that depict Myo1b as a single-headed, tadpole-shaped molecule with outer dimensions of 27.9 x 4.0 nm. Above a certain Myo1b/actin ratio, Myo1b bundles actin filaments presumably by virtue of a second actin-binding site. These studies provide new information regarding the oligomeric state and morphology of Myo1b and support a model in which Myo1b cross-links actin through a cryptic actin-binding site.
Boston Biomedical Research Institute, Watertown, Massachusetts 02472, USA.
Walter F
WF
Stafford
Matt L
ML
Walker
John A
JA
Trinick
Lynne M
LM
Coluccio
D000199:Actins / Q000737:chemistry; D000255:Adenosine Triphosphate / Q000737:chemistry; D000818:Animals; D000838:Anions; D001665:Binding Sites; D002147:Calmodulin / Q000737:chemistry; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D003432:Cross-Linking Reagents / Q000494:pharmacology; D004533:Egtazic Acid / Q000737:chemistry; D004591:Electrophoresis, Polyacrylamide Gel; D008099:Liver / Q000378:metabolism; D008854:Microscopy, Electron; D008958:Models, Molecular; D018482:Muscle, Skeletal / Q000378:metabolism; D024461:Myosin Type I / Q000737:chemistry* / Q000502:physiology; D011485:Protein Binding; D011817:Rabbits; D051381:Rats; D014461:Ultracentrifugation
D000199:Actins; D000838:Anions; D002147:Calmodulin; D003432:Cross-Linking Reagents; D004533:Egtazic Acid; D000255:Adenosine Triphosphate; D024461:Myosin Type I