Identification of novel bifunctional calmodulin-binding and microtubule-stabilizing motifs in STOP proteins.
Although microtubules are intrinsically labile tubulin assemblies, many cell types contain stable polymers, resisting depolymerizing conditions such as exposure to the cold or the drug nocodazole. This microtubule stabilization is largely due to polymer association with STOP proteins. There are several STOP variants, some with capacity to induce microtubule resistance to both the cold and nocodazole, others with microtubule cold stabilizing activity only. These microtubule-stabilizing effects of STOP proteins are inhibited by calmodulin and we now demonstrate that they are determined by two distinct kinds of repeated modular sequences (Mn and Mc), both containing a calmodulin-binding peptide, but displaying different microtubule stabilizing activities. Mn modules induce microtubule resistance to both the cold and nocodazole when expressed in cells. Mc modules, which correspond to the STOP central repeats, have microtubule cold stabilizing activity only. Mouse neuronal STOPs, which induce both cold and drug resistance in cellular microtubules, contain three Mn modules and four Mc modules. Compared with neuronal STOPs, the non-neuronal F-STOP lacks multiple Mn modules and this corresponds with an inability to induce nocodazole resistance. STOP modules represent novel bifunctional calmodulin-binding and microtubule-stabilizing sequences that may be essential for the generation of the different patterns of microtubule stabilization observed in cells.
Bosc
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Commissariat à l'Energie Atomique-Laboratoire du Cytosquelette, INSERM Unité 366, Département de Biologie Moléculaire et Structurale/Cytosquelette, Commissariat à l'Energie Atomique-Grenoble, F-38054 Grenoble cedex 9, France. cbosc@cea.fr
Frank
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Denarier
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E
Ronjat
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Schweitzer
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A
Wehland
J
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Job
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D
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D001665:Binding Sites; D002147:Calmodulin / Q000378:metabolism*; D008869:Microtubule-Associated Proteins / Q000737:chemistry*; D008870:Microtubules / Q000737:chemistry*; D008969:Molecular Sequence Data; D010802:Phylogeny
D002147:Calmodulin; D008869:Microtubule-Associated Proteins; C491893:Mtap6 protein, mouse