Tanner K G, Kyte J
Department of Chemistry 0506, University of California at San Diego, La Jolla, California 92093-0506, USA.
J Biol Chem. 1999 Dec 10;274(50):35985-90. doi: 10.1074/jbc.274.50.35985.
A recombinant fragment of the human receptor for epidermal growth factor containing both its extracellular domain and its membrane-spanning segment, when dissolved with Triton X-100, was observed to dimerize in response to addition of epidermal growth factor (EGF) even at the lowest concentration of this fragment that could be assayed (4 nM). Consequently, the dissociation constant for the dimer of this fragment is at least 10,000-fold smaller than that for dimers of soluble, recombinant forms of the extracellular domain lacking the membrane-spanning segment. The second-order rate constant for dimerization of the fragment containing the extracellular domain and the membrane-spanning segment was estimated to be greater than 0.3 nM(-1) min(-1), more than 10-fold that of the native enzyme under the same conditions. This result suggests that the cytoplasmic domain of the intact enzyme sterically hinders its dimerization. When EGF is removed from the dimer of the fragment, the rate constant for its dissociation is greater than 0.2 min(-1), more than 40-fold that of the native enzyme. This result suggests that interfaces between cytoplasmic domains of intact EGF receptor impart significant stabilization to the dimer of the enzyme.
人表皮生长因子受体的一个重组片段，包含其胞外结构域和跨膜片段，当用Triton X - 100溶解时，即使在可检测的该片段最低浓度（4 nM）下，加入表皮生长因子（EGF）后也会发生二聚化。因此，该片段二聚体的解离常数比缺乏跨膜片段的可溶性重组胞外结构域二聚体的解离常数至少小10000倍。含有胞外结构域和跨膜片段的片段二聚化的二级速率常数估计大于0.3 nM⁻¹ min⁻¹，是相同条件下天然酶的10倍以上。这一结果表明完整酶的胞质结构域在空间上阻碍了其二聚化。当从片段二聚体中去除EGF时，其解离速率常数大于0.2 min⁻¹，是天然酶的40倍以上。这一结果表明完整EGF受体胞质结构域之间的界面赋予了该酶二聚体显著的稳定性。
