This family represents the eukaryotic targeting protein for Xklp2 (TPX2). TPX2 is a microtubule-associated protein that targets a plus end-directed motor (Xklp2) to the minus ends of microtubules in the mitotic spindle. In Xenopus, it has been shown that Xklp2 protein is required for centrosome separation and maintenance of spindle bi-polarity []. It is phosphorylated during mitosis in a microtubule-dependent way []. TPX2 activates Aurora A kinase by promoting its autophosphorylation and protects the phosphorylated residue against dephosphorylation [].
This entry represents the central domain found in the eukaryotic targeting protein for Xklp2 (TPX2) protein. TPX2 is a microtubule-associated protein that targets a plus end-directed motor (Xklp2) to the minus ends of microtubules in the mitotic spindle. This domain is close to the C-terminal of TPX2. The protein importin alpha regulates the activity of TPX2 by binding to the nuclear localisation signal in this domain [].
This entry includes WDL7 from Arabidopsis and related proteins. WDL7 is a TPX2 C-terminal domain containing protein. Similar to WVD2 and other WVD2-like proteins, it contains the KLEEK-motif, which is typical for microtubule-binding proteins []. The function of WDL7 is not clear.
In animals, Targeting Protein for Xklp2 (TPX2) is critical for mitotic spindle assembly. It has a highly conserved TPX2 central domain, an Aurora-A binding domain and a TPX2_C domain that contains a conserved pentapeptide KLEEK motif. However, in plants besides the TPX2 homologue (with three domains), several proteins were found with only the TPX2_C domain. This group of TPX2_C domain only proteins in plants has been named as WDL (or WVD2-like) proteins, as the first identified member is known as WVD2. These WDL proteins bind to microtubules; however, they have lost the function of targeting Xklp2 and were found to play roles in plant development and responses to environment cues [, ].This entry includes WDL4/5/6 from Arabidopsis.
The Aurora-A binding domain in TPX2 (targeting protein for Xklp2)binds to two distinct sites on the Aurora kinase: the upstream residues bind at the N-terminal lobe, whilst the downstream residues bind in an α-helical conformation between the N- and C-terminal lobes. The two Aurora-A binding motifs are connected by a flexible linker that is variable in length and sequence across species. Binding of the domain results strong activation of Aurora-A and protection from deactivating dephosphorylation by phosphatase PP1 [].
This entry represents a conserved region approximately 60 residues long within the eukaryotic targeting protein for Xklp2 (TPX2). Xklp2 is a kinesin-like protein localised on centrosomes throughout the cell cycle and on spindle pole microtubules during metaphase. In Xenopus, it has been shown that Xklp2 protein is required for centrosome separation and maintenance of spindle bi-polarity [, ]. TPX2 is a microtubule-associated protein that mediates the binding of the C-terminal domain of Xklp2 to microtubules. It is phosphorylated during mitosis in a microtubule-dependent way [].
In animals, Targeting Protein for Xklp2 (TPX2) is critical for mitotic spindle assembly. It has a highly conserved TPX2 central domain, an Aurora-A binding domain and a TPX2_C domain that contains a conserved pentapeptide KLEEK motif. However, in plants besides the TPX2 homologue (with three domains), several proteins were found with only the TPX2_C domain. This group of TPX2_C domain only proteins in plants has been named as WDL (or WVD2-like) proteins, as the first identified member is known as WVD2. These WDL proteins bind to microtubules; however, they have lost the function of targeting Xklp2 and were found to play roles in plant development and responses to environment cues [, ].This entry includes WAVE-DAMPENED2 (WVD2) and WDL1/2/3. WVD2, and its closest paralogue WDL1, modulate both rotational polarity and anisotropic cell expansion during organ growth and also promote clockwise root and etiolated hypocotyls coiling, clockwise leaf curling, but left-handed petiole twisting [, ]. WDL3 stabilises microtubules, playing an important role in the regulation of hypocotyl cell elongation. WDL3 levels are regulated by an ubiquitin-26S proteasome-dependent pathway in response to light and functions as a negative regulator of hypocotyl cell elongation in the light [].
