Identification of a neural cell specific variant of microtubule-associated protein 4.
The microtubule-binding domain of MAP4, a ubiquitous microtubule-associated protein, contains a region rich in proline and basic residues (proline-rich region). We searched the bovine adrenal gland for MAP4 isoforms, and identified a novel variant lacking 72 consecutive amino acid residues within the proline-rich region, as compared with the full-length MAP4. The amino acid sequence of the missing region was highly conserved (about 85% identity/similarity) among the corresponding regions of bovine, human, mouse, and rat MAP4, which suggested the functional significance of this region. A comparison of the genomic sequence with the cDNA sequence revealed that the missing region is encoded by a single exon. A MAP4 variant cDNA homologous to the bovine form was also detected in rat cells, suggesting that the new variant can be generated by alternative splicing, not only in bovine but also in other mammalian species. The mRNA expression of the novel isoform was restricted to the brain and the adrenal medulla, suggesting that this isoform is specific to a certain cell type. Using a bacterially expressed fragment corresponding to the microtubule-binding domain of the novel isoform, we analyzed its in vitro characteristics. The fragment induced microtubule assembly and bound to preformed microtubules, but the activities were slightly lower than those of the conventional MAP4 fragment, which carries the full-length proline-rich region. The microtubules assembled in the presence of the fragment failed to be bundled. Instead, a constant spacing between neighboring microtubules was observed.
Matsushima
Kazuyuki
K
Department of Bioscience and Bioinformatics, Faculty of Computer Science and Systems Engineering, Kyushu Institute of Technology, Fukuoka, Japan. a791011k@bse.kyutech.ac.jp
Aosaki
Masafumi
M
Tokuraku
Kiyotaka
K
Hasan
Mohammad Rubayet
MR
Nakagawa
Hiroyuki
H
Kotani
Susumu
S
D000311:Adrenal Glands / Q000737:chemistry; D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D002454:Cell Differentiation; D002460:Cell Line; D017124:Conserved Sequence; D005091:Exons; D014644:Genetic Variation; D008869:Microtubule-Associated Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D008870:Microtubules / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D009474:Neurons / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D016716:PC12 Cells; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011392:Proline / Q000737:chemistry; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D014018:Tissue Distribution; D014404:Tubulin / Q000302:isolation & purification
D008869:Microtubule-Associated Proteins; D009419:Nerve Tissue Proteins; D010446:Peptide Fragments; D020033:Protein Isoforms; D012333:RNA, Messenger; D014404:Tubulin; D011392:Proline