Huang D B, Huxford T, Chen Y Q, Ghosh G
Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0359, USA.
Structure. 1997 Nov 15;5(11):1427-36. doi: 10.1016/s0969-2126(97)00293-1.
Members of the rel/NFkappaB family of transcription factors play a vital role in the regulation of rapid cellular responses, such as those required to fight infection or react to cellular stress. Members of this family of proteins form homo- and heterodimers with differing affinities for dimerization. They share a structural motif known as the rel homology region (RHR), the C-terminal one third of which mediates protein dimerization. Crystal structures of the rel/NFkappaB family members p50 and p65 in their DNA-bound homodimeric form have been solved. These structures showed that the residues from the dimerization domains of both p50 and p65 participate in DNA binding and that the DNA-protein and protein dimerization surfaces form one continuous overlapping interface. We desired to investigate the contribution of DNA to NFkappaB dimerization and to identify the mechanism for the selective association of rel/NFkappaB family peptides into transcriptionally active dimers.
We report here the crystal structures of the dimerization domains of murine p50 and p65 at 2.2 A and 2.0 A resolution, respectively. A comparison of these two structures suggests that conservative amino acid changes at three positions are responsible for the differences in their dimer interfaces. The presence of the target DNA does not change the dimer interface of either protein in any significant manner.
These two structures suggest that the rel/NFkappaB family of transcription factors use only a few conservative changes in their amino acid sequences to form a host of dimers with varying affinities for dimerization. Amino acids at positions corresponding to 254, 267, and 307 of murine p50, function as primary determinants for the observed differences in dimerization affinity. The DNA-contacting charged amino acid sidechains from the dimerization domains are held in a similar conformation in both the DNA-bound and free states, therefore, no major structural rearrangement is required to bring these residues into contact with the DNA.
转录因子rel/NFκB家族成员在快速细胞反应的调节中起着至关重要的作用，比如对抗感染或对细胞应激做出反应时所需的那些反应。该蛋白家族成员形成具有不同二聚化亲和力的同二聚体和异二聚体。它们共享一个被称为rel同源区域（RHR）的结构基序，其C端三分之一介导蛋白质二聚化。rel/NFκB家族成员p50和p65以其DNA结合同二聚体形式的晶体结构已被解析。这些结构表明，p50和p65二聚化结构域的残基都参与DNA结合，并且DNA-蛋白质和蛋白质二聚化表面形成一个连续的重叠界面。我们希望研究DNA对NFκB二聚化的贡献，并确定rel/NFκB家族肽选择性缔合形成转录活性二聚体的机制。
我们在此分别报告了小鼠p50和p65二聚化结构域在2.2 Å和2.0 Å分辨率下的晶体结构。这两种结构的比较表明，三个位置上保守的氨基酸变化导致了它们二聚体界面的差异。靶DNA的存在并没有以任何显著方式改变任何一种蛋白质的二聚体界面。
这两种结构表明，转录因子rel/NFκB家族仅在其氨基酸序列中使用少数保守变化来形成一系列具有不同二聚化亲和力的二聚体。小鼠p50对应位置254、267和307处的氨基酸，是观察到的二聚化亲和力差异的主要决定因素。来自二聚化结构域的与DNA接触的带电荷氨基酸侧链在DNA结合状态和游离状态下都保持相似的构象，因此，不需要进行重大的结构重排就能使这些残基与DNA接触。
