Smooth muscle alpha-tropomyosin crosslinks to caldesmon, to actin and to myosin subfragment 1 on the muscle thin filament.
To obtain proximity information between tropomyosin (Tm) and caldesmon (CaD) on the muscle thin filament, we cloned gizzard alphaTm and created two single Cys mutants S56C/C190S (56Tm) and D100C/C190S (100Tm). They were labeled with benzophenone maleimide (BPM) and UV-irradiated on thin filaments. One chain of BPM-56Tm and two chains of BPM-100Tm crosslinked to CaD. Only BPM-100Tm crosslinked to actin in the absence and presence of CaD and binding of low ratios of myosin subfragment 1 (S1) prevented the crosslinking. Tm-S1 crosslinks were produced when actin.Tm was saturated with S1. Thus, CaD on the actin.Tm filament is located <10 A away from Tm amino acids 56 and 100; in the closed state of the actin.Tm filament, Tm residue 100 is located close to the actin surface and is moved further away in the S1-induced open state; in the open state, S1 binds close to Tm.
Golitsina
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NL
Muscle Research Group, Boston Biomedical Research Institute, Boston, MA 02115, USA.
Lehrer
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SS
D000199:Actins / Q000378:metabolism*; D000818:Animals; D002148:Calmodulin-Binding Proteins / Q000378:metabolism*; D002645:Chickens; D003720:Densitometry; D004926:Escherichia coli / Q000378:metabolism; D007700:Kinetics; D018485:Muscle Fibers, Skeletal / Q000378:metabolism*; D009130:Muscle, Smooth / Q000737:chemistry*; D016296:Mutagenesis; D015879:Myosin Subfragments / Q000378:metabolism* / Q000502:physiology; D011485:Protein Binding; D011994:Recombinant Proteins / Q000378:metabolism; D014335:Tropomyosin / Q000302:isolation & purification / Q000378:metabolism*; D014466:Ultraviolet Rays
D000199:Actins; D002148:Calmodulin-Binding Proteins; D015879:Myosin Subfragments; D011994:Recombinant Proteins; D014335:Tropomyosin