A myofibrillar protein of insect muscle related to vertebrate titin connects Z band and A band: purification and molecular characterization of invertebrate mini-titin.
We show that myofibrils of insect flight and leg muscle contain a doublet of polypeptides with apparent molecular weights of 700K (K = 10(3) Mr) (Hmp I) and 600K (Hmp II), respectively. In Locusta migratoria high ionic strength extraction solubilizes only Hmp II, which is readily purified in native form. It probably reflects a proteolytic derivative of the non-extractable Hmp I. On the basis of its viscosity radius and sedimentation coefficient, Hmp II has a molecular weight of 600K and seems to consist of a single polypeptide chain. The highly asymmetric structure of the molecule is confirmed by rotary shadowing. The flexible rods have a uniform diameter of 3-4 nm and an average length of 260 nm. Polyclonal antibodies show cross-reactivity between Hmp II and its putative precursor Hmp I. We discuss the similarities and differences between the larger titin I/titin II of vertebrate sarcomeric muscle and the smaller Hmp I/Hmp II of invertebrate muscle and conclude that the latter may reflect a mini-titin. In line with the smaller length, immunoelectron microscopy locates the insect mini-titin to the I band and a very short portion of the A band only, while vertebrate titin is known to connect the Z band to the M band. Mini-titin has also been purified from several other insects including Drosophila. Immunofluorescence microscopy on frozen sections shows that mini-titin is present in the sarcomeric muscles of various species from different invertebrate phyla. These include Annelida, Nematomorpha, Plathelmintha, Nemertea and Nematoda like Ascaris lumbricoides and Caenorhabditis elegans. This wide-spread occurrence of invertebrate mini-titin is confirmed by immunoblotting experiments.
Nave
R
R
Max Planck Institute for Biophysical Chemistry, Goettingen, FRG.
Weber
K
K
D000818:Animals; D001200:Ascaris; D001516:Bees; D002645:Chickens; D002850:Chromatography, Gel; D064211:Connectin; D004331:Drosophila melanogaster; D004591:Electrophoresis, Polyacrylamide Gel; D005455:Fluorescent Antibody Technique; D006110:Grasshoppers; D015151:Immunoblotting; D019476:Insect Proteins; D007447:Invertebrate Hormones / Q000302:isolation & purification*; D008970:Molecular Weight; D009124:Muscle Proteins / Q000302:isolation & purification*; D009210:Myofibrils / Q000032:analysis* / Q000648:ultrastructure; D009994:Osmolar Concentration
D064211:Connectin; D019476:Insect Proteins; D007447:Invertebrate Hormones; D009124:Muscle Proteins