title: A FERM domain autoregulates Drosophila myosin 7a activity.
abstract: Full-length Drosophila myosin 7a (myosin 7a-FL) has a complex tail containing a short predicted coiled coil followed by a MyTH4-FERM domain, an SH3 domain, and a C-terminal MyTH4-FERM domain. Myosin 7a-FL expressed in Sf9 cells is monomeric despite the predicted coiled coil. We showed previously that Subfragment-1 (S1) from this myosin has MgATPase of V(max) approximately 1 s(-1) and K(ATPase) approximately 1 microM actin. We find that myosin 7a-FL has V(max) similar to S1 but K(ATPase) approximately 30 microM. Thus, at low actin concentrations (5 microM), the MgATPase of S1 is fully activated, whereas that of myosin 7a-FL is low, suggesting that the tail regulates activity. Electron microscopy of myosin 7a-FL with ATP shows the tail is tightly bent back against the motor domain. Myosin 7a-FL extends at either high ionic strength or without ATP, revealing the motor domain, lever, and tail. A series of C-terminal truncations show that deletion of 99 aa (the MyTH7 subdomain of the C-terminal FERM domain) is sufficient to abolish bending, and the K(ATPase) is then similar to S1. This region is highly conserved in myosin 7a. We found that a double mutation in it, R2140A-K2143A, abolishes bending and reduces K(ATPase) to S1 levels. In addition, the expressed C-terminal FERM domain binds actin with K(d) approximately 30 microM regardless of ATP, similar to the K(ATPase) value for myosin 7a-FL. We propose that at low cellular actin concentrations, myosin 7a-FL is bent and inactive, but at high actin concentrations, it is unfolded and active because the C-terminal FERM domain binds to actin.
authors.affiliation: Laboratory of Molecular Physiology, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Yi
authors.initials: Y
authors.lastname: Yang
authors.forename: Thomas G
authors.initials: TG
authors.lastname: Baboolal
authors.forename: Verl
authors.initials: V
authors.lastname: Siththanandan
authors.forename: Michael
authors.initials: M
authors.lastname: Chen
authors.forename: Matthew L
authors.initials: ML
authors.lastname: Walker
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Knight
authors.forename: Michelle
authors.initials: M
authors.lastname: Peckham
authors.forename: James R
authors.initials: JR
authors.lastname: Sellers
mesh_terms: D000199:Actins / Q000494:pharmacology; D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D029721:Drosophila Proteins; D007313:Insecta; D007700:Kinetics; D000081412:Myosin VIIa; D009218:Myosins / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation / Q000187:drug effects; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D014161:Transduction, Genetic
chemical_list: D000199:Actins; D029721:Drosophila Proteins; D000081412:Myosin VIIa; C000631458:myosin 7a, Drosophila; D000251:Adenosine Triphosphatases; D009218:Myosins