title: The NH2 terminus of titin spans the Z-disc: its interaction with a novel 19-kD ligand (T-cap) is required for sarcomeric integrity.
abstract: Titin is a giant elastic protein in vertebrate striated muscles with an unprecedented molecular mass of 3-4 megadaltons. Single molecules of titin extend from the Z-line to the M-line. Here, we define the molecular layout of titin within the Z-line; the most NH2-terminal 30 kD of titin is located at the periphery of the Z-line at the border of the adjacent sarcomere, whereas the subsequent 60 kD of titin spans the entire width of the Z-line. In vitro binding studies reveal that mammalian titins have at least four potential binding sites for alpha-actinin within their Z-line spanning region. Titin filaments may specify Z-line width and internal structure by varying the length of their NH2-terminal overlap and number of alpha-actinin binding sites that serve to cross-link the titin and thin filaments. Furthermore, we demonstrate that the NH2-terminal titin Ig repeats Z1 and Z2 in the periphery of the Z-line bind to a novel 19-kD protein, referred to as titin-cap. Using dominant-negative approaches in cardiac myocytes, both the titin Z1-Z2 domains and titin-cap are shown to be required for the structural integrity of sarcomeres, suggesting that their interaction is critical in titin filament-regulated sarcomeric assembly.
authors.affiliation: Departments of Cell Biology and Anatomy, and Molecular and Cellular Biology, University of Arizona, Tucson, Arizona 85724, USA. gregorio@u.arizona.edu
authors.forename: C C
authors.initials: CC
authors.lastname: Gregorio
authors.forename: K
authors.initials: K
authors.lastname: Trombitás
authors.forename: T
authors.initials: T
authors.lastname: Centner
authors.forename: B
authors.initials: B
authors.lastname: Kolmerer
authors.forename: G
authors.initials: G
authors.lastname: Stier
authors.forename: K
authors.initials: K
authors.lastname: Kunke
authors.forename: K
authors.initials: K
authors.lastname: Suzuki
authors.forename: F
authors.initials: F
authors.lastname: Obermayr
authors.forename: B
authors.initials: B
authors.lastname: Herrmann
authors.forename: H
authors.initials: H
authors.lastname: Granzier
authors.forename: H
authors.initials: H
authors.lastname: Sorimachi
authors.forename: S
authors.initials: S
authors.lastname: Labeit
mesh_terms: D000185:Actinin / Q000737:chemistry / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D002478:Cells, Cultured; D002642:Chick Embryo; D064211:Connectin; D015870:Gene Expression / Q000502:physiology; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016253:Microscopy, Immunoelectron; D008969:Molecular Sequence Data; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000378:metabolism / Q000648:ultrastructure; D009124:Muscle Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000737:chemistry / Q000166:cytology / Q000378:metabolism; D009206:Myocardium / Q000737:chemistry / Q000166:cytology / Q000378:metabolism; D009210:Myofibrils / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D011494:Protein Kinases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D012518:Sarcomeres / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure; D014158:Transcription, Genetic / Q000502:physiology
chemical_list: D064211:Connectin; D008565:Membrane Proteins; D009124:Muscle Proteins; D000185:Actinin; D011494:Protein Kinases