The NH2 terminus of titin spans the Z-disc: its interaction with a novel 19-kD ligand (T-cap) is required for sarcomeric integrity.
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.
Gregorio
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CC
Departments of Cell Biology and Anatomy, and Molecular and Cellular Biology, University of Arizona, Tucson, Arizona 85724, USA. gregorio@u.arizona.edu
Trombitás
K
K
Centner
T
T
Kolmerer
B
B
Stier
G
G
Kunke
K
K
Suzuki
K
K
Obermayr
F
F
Herrmann
B
B
Granzier
H
H
Sorimachi
H
H
Labeit
S
S
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
D064211:Connectin; D008565:Membrane Proteins; D009124:Muscle Proteins; D000185:Actinin; D011494:Protein Kinases