I-protein forms cage-like aggregates of myosin in vitro.
I-protein was mixed with myosin before or after myosin filaments were reconstituted. In both cases, I-protein seemed to accelerate the myosin assembly. The binding of I-protein to myosin filaments was tested by sedimentation experiments and SDS-polyacrylamide gel electrophoresis. In a low ionic strength solution at pH 6.5, the binding ratio of I-protein to myosin was 1:40 by molar ratio when the I-protein molecules highly specifically bound to myosin filaments. I-protein could maximally bind to myosin filaments at the molar ratio of 1:2.7. In this case, excess I-protein molecules remained in the supernatant after sedimentation, although the unbound I-protein could still bind to myosin filaments. Electron microscopic observations revealed that I-protein bundled myosin filaments in the low ionic strength solution (pH 6.5). Cage-like structures which were very similar to the Mg-paracrystals of non-muscle myosins were formed at pH 7.2. In gel filtration, the apparent molecular mass of I-protein was 100 kDa, while it was 50 kDa in SDS gel electrophoresis. Therefore, I-protein is regarded to be a homodimer of a 50 kDa subunit and can divalently bind to myosin molecules.
Ohashi
K
K
Department of Biology, Faculty of Science, Chiba University.
Ishikawa
K
K
Maruyama
K
K
D008841:Actin Cytoskeleton / Q000648:ultrastructure; D000818:Animals; D055598:Chemical Phenomena; D011232:Chemical Precipitation; D002621:Chemistry; D002645:Chickens; D002850:Chromatography, Gel / Q000379:methods; D006863:Hydrogen-Ion Concentration; D008854:Microscopy, Electron; D008970:Molecular Weight; D009124:Muscle Proteins / Q000502:physiology*; D009218:Myosins / Q000096:biosynthesis* / Q000648:ultrastructure; D011189:Potassium Chloride / Q000494:pharmacology; D011485:Protein Binding; D011817:Rabbits
D009124:Muscle Proteins; C046447:myofibrillar I-protein, Gallus gallus; C489068:myofibrillar I-protein, Oryctolagus cuniculus; D011189:Potassium Chloride; D009218:Myosins