Structure and function of the 10 S conformation of smooth muscle myosin.
Smooth myosin regulatory light chain (RLC) was exchanged with RLC labeled with benzophenone-4-iodoacetamide at Cys-108. Irradiation under conditions that favor the folded (10 S) conformation resulted in 10 S cross-linked myosin that could not unfold. Purified 10 S cross-linked myosin was cross-linked between the RLC of one head to light meromyosin between leucine 1554 and glutamate 1583, adjacent to a predicted noncoiled region, approximately 60 nm from the tip of the tail. At high ionic strength without actin, product release from one-half of the heads was slow (like 10 S) whereas the other half were activated. This suggests that tail binding to the RLC carboxyl-terminal domain stabilizes ionic interactions important to slow nucleotide release. With actin, product release from both (un)phosphorylated 10 S cross-linked myosin was from one slow population similar to unphosphorylated filaments. 10 S cross-linked myosin weakly bound actin (dissociation constant > 500 microM) and did not move actin in vitro. Single-headed myosin did not fold or trap nucleotide. These and other data suggest that "trapping" occurs only with both heads and the tail binds to a newly formed site, which includes the RLC carboxyl-terminal domain, once trapping has occurred.
Olney
J J
JJ
Department of Biochemistry and Biophysics, Washington State University, Pullman, Washington 99164-4660, USA.
Sellers
J R
JR
Cremo
C R
CR
D000199:Actins / Q000737:chemistry; D000595:Amino Acid Sequence; D000818:Animals; D002645:Chickens; D003432:Cross-Linking Reagents; D005573:Formycins / Q000378:metabolism; D008969:Molecular Sequence Data; D009130:Muscle, Smooth / Q000737:chemistry / Q000648:ultrastructure*; D018995:Myosin Heavy Chains / Q000737:chemistry; D018994:Myosin Light Chains / Q000737:chemistry; D009218:Myosins / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure*; D009994:Osmolar Concentration; D010449:Peptide Mapping; D010777:Photochemistry; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D012265:Ribonucleotides / Q000378:metabolism; D013329:Structure-Activity Relationship
D000199:Actins; D003432:Cross-Linking Reagents; D005573:Formycins; D018994:Myosin Light Chains; D012265:Ribonucleotides; C032552:formycin triphosphate; D018995:Myosin Heavy Chains; D009218:Myosins