CLIPs and CLASPs and cellular dynamics

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Abstract
Microtubules are polar, filamentous fibres. They are dynamic structures that are important for widely different processes, which include mitosis, cell migration, neuronal differentiation and transport of cargo. The dynamic properties of microtubules are, in part, regulated by plus-end tracking proteins (+TIPs), which associate with the distal ends of microtubules. Many of the +TIPs interact with each other as well as with microtubules. Different mechanisms account for the specific association of +TIPs with the microtubule end. Among these are 'treadmilling', motor-protein-mediated delivery and 'hitch hiking'. Cytoplasmic linker proteins (CLIPs) interact with CLIP-associating proteins (CLASPs) and both are conserved +TIPs. CLIPs and CLASPs might cooperate to regulate cellular asymmetry. CLIP170 and CLIP115 are homodimers that contain very similar N-terminal microtubule-binding motifs, an elongated coiled-coil domain, but differing C termini. They are general promoters of microtubule growth. The structure of CLASPs has been less well defined. CLASPs are regulatable proteins and are involved in stabilizing a subset of microtubules at highly specific cellular sites in response to signalling cues. These sites include mitotic kinetochores, as well as microtubule ends at the leading edge of fibroblasts and neuronal growth cones.