TIP maker and TIP marker; EB1 as a master controller of microtubule plus ends

Department of Biological Sciences, University of Notre Dame, Notre Dame, IN 46556, USA.
The Journal of Cell Biology (Impact Factor: 9.83). 11/2005; 171(2):197-200. DOI: 10.1083/jcb.200509150
Source: PubMed


The EB1 protein is a member of the exciting and enigmatic family of microtubule (MT) tip-tracking proteins. EB1 acts as an exquisite marker of dynamic MT plus ends in some cases, whereas in others EB1 is thought to directly dictate the behavior of the plus ends. How EB1 differentiates between these two roles remains unclear; however, a growing list of interactions between EB1 and other MT binding proteins suggests there may be a single mechanism. Adding another layer of complexity to these interactions, two studies published in this issue implicate EB1 in cross-talk between mitotic MTs and between MTs and actin filaments (Goshima et al., p. 229; Wu et al., p. 201). These results raise the possibility that EB1 is a central player in MT-based transport, and that the activity of MT-binding proteins depends on their ability or inability to interact with EB1.

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Available from: Kevin Vaughan, Jun 22, 2015
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    • "In addition to the plant-specific SPR +TIPs, plants express End Binding (EB) proteins, which are evolutionarily and structurally conserved +TIPs present in plants, animals, and fungi. EB proteins are thought of as master regulators of MT plus ends (Vaughan, 2005; Slep, 2010). The genome of Arabidopsis encodes three EB proteins named EB1a, EB1b, and EB1c. "
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    ABSTRACT: The microtubule plus-end tracking proteins (+TIPs) END BINDING1b (EB1b) and SPIRAL1 (SPR1) are required for normal cell expansion and organ growth. EB proteins are viewed as central regulators of +TIPs and cell polarity in animals; SPR1 homologs are specific to plants. To explore if EB1b and SPR1 fundamentally function together, we combined genetic, biochemical, and cell imaging approaches in Arabidopsis thaliana. We found that eb1b-2 spr1-6 double mutant roots exhibit substantially more severe polar expansion defects than either single mutant, undergoing right-looping growth and severe axial twisting instead of waving on tilted hard-agar surfaces. Protein interaction assays revealed that EB1b and SPR1 bind each other and tubulin heterodimers, which is suggestive of a microtubule loading mechanism. EB1b and SPR1 show antagonistic association with microtubules in vitro. Surprisingly, our combined analyses revealed that SPR1 can load onto microtubules and function independently of EB1 proteins, setting SPR1 apart from most studied +TIPs in animals and fungi. Moreover, we found that the severity of defects in microtubule dynamics in spr1 eb1b mutant hypocotyl cells correlated well with the severity of growth defects. These data indicate that SPR1 and EB1b have complex interactions as they load onto microtubule plus ends and direct polar cell expansion and organ growth in response to directional cues.
    The Plant Cell 11/2014; 26(11). DOI:10.1105/tpc.114.131482 · 9.34 Impact Factor
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    • "This protein was originally identified as a binding partner of APC (adenomatous polyposis coli) [4] and was later shown to track growing microtubule plus ends in cells [5]. It has been shown that EB1 plays a central role in regulation at microtubule plus ends [6], as it can bind microtubule plus ends directly [7] and can recruit various proteins with a range of structures and functions. Two sequence motifs have been identified which mediate the interaction with EB1, namely the CAP-Gly domain and the SxIP motif [8]–[10]. "
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    ABSTRACT: Little is known about how microtubules are regulated in different cell types during development. EB1 plays a central role in the regulation of microtubule plus ends. It directly binds to microtubule plus ends and recruits proteins which regulate microtubule dynamics and behaviour. We report the identification of Kank, the sole Drosophila orthologue of human Kank proteins, as an EB1 interactor that predominantly localises to embryonic attachment sites between muscle and tendon cells. Human Kank1 was identified as a tumour suppressor and has documented roles in actin regulation and cell polarity in cultured mammalian cells. We found that Drosophila Kank binds EB1 directly and this interaction is essential for Kank localisation to microtubule plus ends in cultured cells. Kank protein is expressed throughout fly development and increases during embryogenesis. In late embryos, it accumulates to sites of attachment between muscle and epidermal cells. A kank deletion mutant was generated. We found that the mutant is viable and fertile without noticeable defects. Further analysis showed that Kank is dispensable for muscle function in larvae. This is in sharp contrast to C. elegans in which the Kank orthologue VAB-19 is required for development by stabilising attachment structures between muscle and epidermal cells.
    PLoS ONE 09/2014; 9(9):e106112. DOI:10.1371/journal.pone.0106112 · 3.23 Impact Factor
    • "EB1 localizes to the microtubule plus end, at least in part, by recognizing the nucleotide state of tubulin in the microtubule lattice [Zanic et al., 2009; Maurer et al., 2011, 2012]. There is evidence that the EB1 N-terminal domain binds to the microtubule preferentially through interactions with the GTP-rich cap, whereas the C-terminal domain acts as a microtubule tip localization signal and enables binding to many other 1TIPs [Hayashi and Ikura, 2003; Vaughan, 2005; Honnappa et al., 2009; Zanic et al., 2009]. EB1 impacts numerous biological functions including the suppression of microtubule dynamic instability [Manna et al., 2008], regulation of microtubule dynamics and chromosomal stability [Leterrier et al., 2011], as well as maintenance of cell polarity through activation of protein kinase C [Schober et al., 2012]. "
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    ABSTRACT: Using the nonhydrolyzable GTP analog GMPCPP and the slowly hydrolyzable GTPγS, we polymerize microtubules that recapitulate the end binding behavior of the plus end interacting protein (+TIP) EB1 along their entire length, and use these to investigate the impact of EB1 binding on microtubule mechanics. To measure the stiffness of single filaments, we use a spectral analysis method to determine the ensemble of shapes adopted by a freely diffusing, fluorescently-labeled microtubule. We find that the presence of EB1 can stiffen microtubules in a manner that depends on the hydrolysis state of the tubulin-bound nucleotide, as well as the presence of the small-molecule stabilizer paclitaxel. We find that the magnitude of the EB1-induced stiffening is not proportional to the EB1-microtubule binding affinity, suggesting that the stiffening effect does not arise purely from an increase in the total amount of bound EB1. Additionally, we find that EB1 binds cooperatively to microtubules in manner that depends on tubulin-bound nucleotide state. © 2014 Wiley Periodicals, Inc.
    Cytoskeleton 09/2014; 71(9). DOI:10.1002/cm.21190 · 3.12 Impact Factor
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