440-kD ankyrinB: structure of the major developmentally regulated domain and selective localization in unmyelinated axons.
440-kD ankyrinB is an alternatively spliced variant of 220-kD ankyrinB, with a predicted 220-kD sequence inserted between the membrane/spectrin binding domains and COOH-terminal domain (Kunimoto, M., E. Otto, and V. Bennett. 1991. J. Cell Biol. 236:1372-1379). This paper presents the sequence of 2085 amino acids comprising the alternatively spliced portion of 440-kD ankyrinB, and provides evidence that much of the inserted sequence has the configuration of an extended random coil. Notable features of the inserted sequence include a hydrophilicity profile that contains few hydrophobic regions, and 220 predicted sites for phosphorylation by protein kinases (casein kinase 2, protein kinase C, and proline-directed protein kinase). Secondary structure and folding of the inserted amino acid residues were deduced from properties of recombinant polypeptides. Frictional ratios of 1.9-2.4 were calculated from Stokes radii and sedimentation coefficients, for polypeptides comprising 70% of the inserted sequence, indicating a highly asymmetric shape. Circular dichroism spectra of these polypeptides indicate a nonglobular structure with negligible alpha-helix or beta sheet folding. These results suggest a ball-and-chain model for 440-kD ankyrinB with a membrane-associated globular head domain and an extended filamentous tail domain encoded by the inserted sequence. Immunofluorescence and immunoblot studies of developing neonatal rat optic nerve indicate that 440-kD ankyrinB is selectively targeted to premyelinated axons, and that 440-kD ankyrinB disappears from these axons coincident with myelination. Hypomyelinated nerve tracts of the myelin-deficient Shiverer mice exhibit elevated levels of 440-kD ankyrinB. 440-kD ankyrinB thus is a specific component of unmyelinated axons and expression of 440-kD ankyrinB may be downregulated as a consequence of myelination.
Chan
W
W
Howard Hughes Medical Institute, Duke University Medical Center, Durham, North Carolina 27710.
Kordeli
E
E
Bennett
V
V
D000595:Amino Acid Sequence; D000818:Animals; D017487:Ankyrins / Q000737:chemistry* / Q000378:metabolism; D001369:Axons / Q000378:metabolism*; D001665:Binding Sites; D002942:Circular Dichroism; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D006801:Humans; D051379:Mice; D008818:Mice, Neurologic Mutants / Q000378:metabolism; D008969:Molecular Sequence Data; D009900:Optic Nerve / Q000378:metabolism; D017433:Protein Structure, Secondary; D051381:Rats; D011994:Recombinant Proteins; D012995:Solubility; D013329:Structure-Activity Relationship
D017487:Ankyrins; D018076:DNA, Complementary; D011994:Recombinant Proteins