title: Probing muscle ankyrin-repeat protein (MARP) structure and function.
abstract: Muscle ankyrin-repeat proteins (MARPs) have been shown to serve diverse functions within cardiac and skeletal muscle cells. Apart from their interactions with sarcomeric proteins like titin or myopalladin that locate them along myofilaments, MARPs are able to shuttle to the nucleus where they act as modulators for a variety of transcription factors. The deregulation of MARPs in many cardiac and skeletal myopathies contributes to their use as biomarkers for these diseases. Many of their functions are attributed to their domain composition. MARPs consist of an N-terminal coiled-coil domain responsible for their dimerization. The C-terminus contains a series of ankyrin repeats, whose best-characterized function is to bind to the N2A region of the giant sarcomeric protein titin. Here we investigate the nature of their dimerization and their interaction with titin more closely. We demonstrate that the coiled-coil domain in all MARPs enables their homo- and hetero-dimerization in antiparallel fashion. Protein complementation experiments indicate further antiparallel binding of the ankyrin repeats to titin's N2A region. Binding of MARP to titin also affects its PKA mediated phosphorylation. We demonstrate further that MARPs themselves are phosphorylated by PKA and PKC, potentially altering their structure or function. These studies elucidate structural relationships within the stretch-responsive MARP/titin complex in cross-striated muscle cells, and may relate to disease relevant posttranslational modifications of MARPs and titin that alter muscle compliance.
authors.affiliation: School of Medicine, University of California San Diego, La Jolla, California.
authors.forename: Alexander Shiang
authors.initials: AS
authors.lastname: Lun
authors.forename: Ju
authors.initials: J
authors.lastname: Chen
authors.forename: Stephan
authors.initials: S
authors.lastname: Lange
mesh_terms: D000818:Animals; D017089:Ankyrin Repeat; D001665:Binding Sites; D019556:COS Cells; D002522:Chlorocebus aethiops; D064211:Connectin / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D006801:Humans; D009124:Muscle Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism*; D009154:Mutation; D009206:Myocardium / Q000378:metabolism*; D009687:Nuclear Proteins / Q000378:metabolism; D010766:Phosphorylation; D011487:Protein Conformation; D054730:Protein Interaction Domains and Motifs; D011493:Protein Kinase C / Q000378:metabolism; D055503:Protein Multimerization; D011499:Protein Processing, Post-Translational; D012097:Repressor Proteins / Q000378:metabolism; D013329:Structure-Activity Relationship; D014162:Transfection
chemical_list: C491304:ANKRD1 protein, human; C432364:ANKRD2 protein, human; C472289:ANKRD23 protein, human; D064211:Connectin; D009124:Muscle Proteins; D009687:Nuclear Proteins; D012097:Repressor Proteins; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C
keywords: MARP; kinase; muscle; phosphorylation; titin