The microtubule (MT) plus-end is a crucial site for the regulation of MT dynamics and interactions by several groups of plus-end tracking proteins (+TIPs). These +TIPs form comet-like accumulations at the plus ends of MTs to regulate MT dynamics and interactions with organelles and macromolecular complexes. The +TIPs include diverse groups of proteins, such as motor and nonmotor proteins, MT polymerases and depolymerases as well as various regulatory and adaptor proteins. The CLIP-associated protein (CLASP) family includes CLASP1 and CLASP2 proteins, which are expressed as long (alpha) and short (beta) isoforms. Thse +TIPs conatin an N-terminal TOG domain, multiple TOG-like domains, and a basic and serine-rich motif (SxIP). The TOG domain facilitates interaction with tubulin dimers, while the SxIP motif promotes interaciton with EB1 and MTs. A C-terminal domain is involved in interaction with CLIPs, as well as several other proteins. CLASPs are MT stabilizing fators that localize to mitotic spindles, kinetochores, and the midbody. CLASPs are important for cell division, and may regulate cell migration and neuronal growth cone motility.
