The Arabidopsis microtubule-associated protein AtMAP65-1: molecular analysis of its microtubule bundling activity.
The 65-kD microtubule-associated protein (MAP65) family is a family of plant microtubule-bundling proteins. Functional analysis is complicated by the heterogeneity within this family: there are nine MAP65 genes in Arabidopsis thaliana, AtMAP65-1 to AtMAP65-9. To begin the functional dissection of the Arabidopsis MAP65 proteins, we have concentrated on a single isoform, AtMAP65-1, and examined its effect on the dynamics of mammalian microtubules. We show that recombinant AtMAP65-1 does not promote polymerization and does not stabilize microtubules against cold-induced microtubule depolymerization. However, we show that it does induce microtubule bundling in vitro and that this protein forms 25-nm cross-bridges between microtubules. We further demonstrate that the microtubule binding region resides in the C-terminal half of the protein and that Ala409 and Ala420 are essential for the interaction with microtubules. Ala420 is a conserved amino acid in the AtMAP65 family and is mutated to Val in the cytokinesis-defective mutant pleiade-4 of the AtMAP65-3/PLEIADE gene. We show that AtMAP65-1 can form dimers and that a region in the N terminus is responsible for this activity. Neither the microtubule binding region nor the dimerization region alone could induce microtubule bundling, strongly suggesting that dimerization is necessary to produce the microtubule cross-bridges. In vivo, AtMAP65-1 is ubiquitously expressed both during the cell cycle and in all plant organs and tissues with the exception of anthers and petals. Moreover, using an antiserum raised to AtMAP65-1, we show that AtMAP65-1 binds microtubules at specific stages of the cell cycle.
Integrative Cell Biology Laboratory, School of Biological and Biomedical Sciences, University of Durham, South Road, Durham DH1 3LE, United Kingdom.
Andrei P
AP
Smertenko
Hsin-Yu
HY
Chang
Vera
V
Wagner
Despina
D
Kaloriti
Stepan
S
Fenyk
Seiji
S
Sonobe
Clive
C
Lloyd
Marie-Theres
MT
Hauser
Patrick J
PJ
Hussey
D000595:Amino Acid Sequence; D000818:Animals; D017360:Arabidopsis / Q000166:cytology / Q000235:genetics / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D002453:Cell Cycle / Q000502:physiology; D002478:Cells, Cultured; D019281:Dimerization; D018506:Gene Expression Regulation, Plant; D008869:Microtubule-Associated Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008870:Microtubules / Q000378:metabolism*; D008969:Molecular Sequence Data; D011485:Protein Binding; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020836:Protein Structure, Quaternary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D013552:Swine; D014404:Tubulin / Q000378:metabolism
D029681:Arabidopsis Proteins; C492901:MAP65-1 protein, Arabidopsis; D008869:Microtubule-Associated Proteins; D020033:Protein Isoforms; D011994:Recombinant Proteins; D014404:Tubulin