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Journal of Cell Science, Vol 95, Issue 4 535-544, Copyright © 1990 by Company of Biologists
JOURNAL ARTICLES |
R Nave and K Weber
Max Planck Institute for Biophysical Chemistry, Goettingen, FRG.
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.
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C Ferguson, A Lakey, A Hutchings, G. Butcher, K. Leonard, and B Bullard Cytoskeletal proteins of insect muscle: location of zeelins in Lethocerus flight and leg muscle J. Cell Sci., January 5, 1994; 107(5): 1115 - 1129. [Abstract] [PDF]
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U Vinkemeier, W Obermann, K Weber, and D. Furst The globular head domain of titin extends into the center of the sarcomeric M band. cDNA cloning, epitope mapping and immunoelectron microscopy of two titin-associated proteins J. Cell Sci., January 9, 1993; 106(1): 319 - 330. [Abstract] [PDF]
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