Stokes Philippa H, Thompson Lyndal S, Marianayagam Neelan J, Matthews Jacqueline M
School of Molecular and Microbial Biosciences, University of Sydney, NSW 2006, Australia.
Biochem Biophys Res Commun. 2007 Mar 2;354(1):197-202. doi: 10.1016/j.bbrc.2006.12.178. Epub 2007 Jan 4.
CtIP is a tumor suppressor that interacts with Retinoblastoma protein (Rb) to regulate the G1/S-phase transition of the cell cycle. Despite its large size (897 residues) CtIP has few known structured regions. Rather it contains several linear motifs that interact with known binding partners, including an LXCXE motif that binds the pocket domain of Rb-family proteins. This LXCXE motif lies at the C-terminus of the only known structured domain, an N-terminal coiled-coil dimerization domain (DD; residues 45-160). Yeast two-hybrid (Y2H) and GST-pulldown analyses showed that CtIP requires the LXCXE motif to bind the Rb-pocket. Although isothermal titration calorimetry data indicates that the LXCXE motif is the sole determinant of binding affinity for the Rb-pocket domain (K(A) approximately 10(6)M(-1)), Y2H data indicates that the DD is required to stabilize the interaction in vivo. Thus dimerization may increase the apparent stability of the proteins and/or the lifetime of the complexes.
CtIP是一种肿瘤抑制因子，它与视网膜母细胞瘤蛋白（Rb）相互作用，以调节细胞周期的G1/S期转换。尽管CtIP体积较大（897个氨基酸残基），但其已知的结构化区域很少。相反，它包含几个与已知结合伴侣相互作用的线性基序，包括一个与Rb家族蛋白的口袋结构域结合的LXCXE基序。这个LXCXE基序位于唯一已知的结构化结构域的C末端，即一个N末端卷曲螺旋二聚化结构域（DD；氨基酸残基45-160）。酵母双杂交（Y2H）和GST下拉分析表明，CtIP需要LXCXE基序来结合Rb口袋。尽管等温滴定量热法数据表明LXCXE基序是与Rb口袋结构域结合亲和力的唯一决定因素（K(A)约为10(6)M(-1)），但Y2H数据表明DD在体内是稳定这种相互作用所必需的。因此，二聚化可能会增加蛋白质的表观稳定性和/或复合物的寿命。
