title: Function of the head-tail junction in the activity of myosin II.
abstract: All class II myosins have the conserved amino acid sequence Pro-Leu-Leu at their head-tail junctions. We systematically altered this sequence in smooth muscle heavy meromyosin (HMM) by site-directed mutagenesis and examined the effects of these mutations on actin-myosin interactions. Deletion of the proline and second leucine did not cause any noticeable change in either actin-activated ATPase activity or actin-sliding velocity. In contrast, deletion of the two leucine residues and substitution of the first leucine with alanine resulted in a 14-fold and 5-fold decrease, respectively, in actin-activated ATPase activity. However, both these mutations did not appreciably affect actin-sliding velocity, which was consistent with a result that there was no considerable change in the ADP release rate from acto-HMM in the deletion mutant. In contrast to double-headed HMM, a single-headed subfragment-1 (S1) with a Leu-Leu deletion mutation exhibited actin activated ATPase activity similar to that by wild type S1. Our results suggest that the first leucine of the conserved Leu-Leu sequence at the head-tail junction profoundly affects the cooperativity between the two heads involved in the actin activated ATPase activity of myosin II.
authors.affiliation: Department of Biology, Graduate School of Science, Chiba University, Inage-ku, Chiba 263-8522, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Haraguchi
authors.forename: Kei
authors.initials: K
authors.lastname: Honda
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Wanikawa
authors.forename: Nao
authors.initials: N
authors.lastname: Shoji
authors.forename: Keiichi
authors.initials: K
authors.lastname: Yamamoto
authors.forename: Kohji
authors.initials: K
authors.lastname: Ito
mesh_terms: D000199:Actins / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D002645:Chickens; D017124:Conserved Sequence; D007930:Leucine / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D011392:Proline / Q000235:genetics / Q000378:metabolism; D024745:Smooth Muscle Myosins / Q000235:genetics / Q000378:metabolism*
chemical_list: D000199:Actins; D011392:Proline; D000251:Adenosine Triphosphatases; D024745:Smooth Muscle Myosins; D007930:Leucine
keywords: ATPase; Actin; Coiled-coil; HMM; In vitro motility; Myosin; S1; Smooth muscle; WT; heavy meromyosin; subfragment-1; wild type