Schrag Joseph D, Jiralerspong Sarn, Banville Myriam, Jaramillo Maria Luz, O'Connor-McCourt Maureen D
Biotechnology Research Institute, National Research Council Canada, 6100 Royalmount Avenue, Montreal, QC, Canada.
Proc Natl Acad Sci U S A. 2008 May 6;105(18):6566-71. doi: 10.1073/pnas.0800086105. Epub 2008 Apr 29.
Gadd45 proteins are recognized as tumor and autoimmune suppressors whose expression can be induced by genotoxic stresses. These proteins are involved in cell cycle control, growth arrest, and apoptosis through interactions with a wide variety of binding partners. We report here the crystal structure of Gadd45gamma, which reveals a fold comprising an alphabetaalpha sandwich with a central five-stranded mixed beta-sheet with alpha-helices packed on either side. Based on crystallographic symmetry we identified the dimer interface of Gadd45gamma dimers by generating point mutants that compromised dimerization while leaving the tertiary structure of the monomer intact. The dimer interface comprises a four-helix bundle involving residues that are the most highly conserved among Gadd45 isoforms. Cell-based assays using these point mutants demonstrate that dimerization is essential for growth inhibition. This structural information provides a new context for evaluation of the plethora of protein-protein interactions that govern the many functions of the Gadd45 family of proteins.
Gadd45蛋白被认为是肿瘤和自身免疫抑制因子，其表达可由基因毒性应激诱导。这些蛋白通过与多种结合伴侣相互作用，参与细胞周期调控、生长停滞和细胞凋亡。我们在此报道了Gadd45γ的晶体结构，该结构揭示了一种折叠结构，由一个αβ-α三明治结构组成，中间有一个五链混合β-折叠片层，两侧堆积着α-螺旋。基于晶体学对称性，我们通过产生破坏二聚化但保持单体三级结构完整的点突变体，确定了Gadd45γ二聚体的二聚体界面。二聚体界面由一个四螺旋束组成，涉及Gadd45异构体中最保守的残基。使用这些点突变体进行的基于细胞的分析表明，二聚化对于生长抑制至关重要。这一结构信息为评估众多调控Gadd45蛋白家族多种功能的蛋白质-蛋白质相互作用提供了新的背景。
