Three-dimensional structure of Acanthamoeba castellanii myosin-IB (MIB) determined by cryoelectron microscopy of decorated actin filaments.
The Acanthamoeba castellanii myosin-Is were the first unconventional myosins to be discovered, and the myosin-I class has since been found to be one of the more diverse and abundant classes of the myosin superfamily. We used two-dimensional (2D) crystallization on phospholipid monolayers and negative stain electron microscopy to calculate a projection map of a "classical" myosin-I, Acanthamoeba myosin-IB (MIB), at approximately 18 A resolution. Interpretation of the projection map suggests that the MIB molecules sit upright on the membrane. We also used cryoelectron microscopy and helical image analysis to determine the three-dimensional structure of actin filaments decorated with unphosphorylated (inactive) MIB. The catalytic domain is similar to that of other myosins, whereas the large carboxy-terminal tail domain differs greatly from brush border myosin-I (BBM-I), another member of the myosin-I class. These differences may be relevant to the distinct cellular functions of these two types of myosin-I. The catalytic domain of MIB also attaches to F-actin at a significantly different angle, approximately 10 degrees, than BBM-I. Finally, there is evidence that the tails of adjacent MIB molecules interact in both the 2D crystal and in the decorated actin filaments.
Jontes
J D
JD
Department of Cell Biology, The Scripps Research Institute, La Jolla, California 92037, USA.
Ostap
E M
EM
Pollard
T D
TD
Milligan
R A
RA
D000048:Acanthamoeba; D000199:Actins / Q000648:ultrastructure*; D000818:Animals; D003460:Crystallization; D005615:Freezing; D008854:Microscopy, Electron; D008871:Microvilli / Q000737:chemistry / Q000648:ultrastructure; D008958:Models, Molecular; D009218:Myosins / Q000302:isolation & purification / Q000648:ultrastructure*; D010743:Phospholipids; D011487:Protein Conformation
D000199:Actins; D010743:Phospholipids; D009218:Myosins