An unusual transduction pathway in human tonic smooth muscle myosin. Biophys J 2007 Nov 15;93(10):3555-66
Date
08/21/2007Pubmed ID
17704147Pubmed Central ID
PMC2072059DOI
10.1529/biophysj.106.100818Scopus ID
2-s2.0-36549073805 (requires institutional sign-in at Scopus site) 2 CitationsAbstract
The motor protein myosin binds actin and ATP, producing work by causing relative translation of the proteins while transducing ATP free energy. Smooth muscle myosin has one of four heavy chains encoded by the MYH11 gene that differ at the C-terminus and in the active site for ATPase due to alternate splicing. A seven-amino-acid active site insert in phasic muscle myosin is absent from the tonic isoform. Fluorescence increase in the nucleotide sensitive tryptophan (NST) accompanies nucleotide binding and hydrolysis in several myosin isoforms implying it results from a common origin within the motor. A wild-type tonic myosin (smA) construct of the enzymatic head domain (subfragment 1 or S1) has seven tryptophan residues and nucleotide-induced fluorescence enhancement like other myosins. Three smA mutants probe the molecular basis for the fluorescence enhancement. W506+ contains one tryptophan at position 506 homologous to the NST in other myosins. W506F has the native tryptophans except phenylalanine replaces W506, and W506+(Y499F) is W506+ with phenylalanine replacing Y499. W506+ lacks nucleotide-induced fluorescence enhancement probably eliminating W506 as the NST. W506F has impaired ATPase activity but retains nucleotide-induced fluorescence enhancement. Y499F replacement in W506+ partially rescues nucleotide sensitivity demonstrating the role of Y499 as an NST facilitator. The exceptional response of W506 to active site conformation opens the possibility that phasic and tonic isoforms differ in how influences from active site ATPase propagate through the protein network.
Author List
Halstead MF, Ajtai K, Penheiter AR, Spencer JD, Zheng Y, Morrison EA, Burghardt TPAuthor
Emma A. Morrison PhD Associate Professor in the Biochemistry department at Medical College of WisconsinMESH terms used to index this publication - Major topics in bold
Adenosine TriphosphateBaculoviridae
Binding Sites
DNA Primers
Expressed Sequence Tags
Humans
Models, Biological
Models, Chemical
Muscle, Smooth
Mutagenesis, Site-Directed
Myosins
Phenylalanine
Protein Conformation
Protein Isoforms
Proteins
Signal Transduction
