Sfyroera Georgia, Katragadda Madan, Morikis Dimitrios, Isaacs Stuart N, Lambris John D
Department of Pathology and Laboratory Medicine,University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA.
J Immunol. 2005 Feb 15;174(4):2143-51. doi: 10.4049/jimmunol.174.4.2143.
Regulation of complement activation by pathogens and the host are critical for survival. Using two highly related orthopoxvirus proteins, the vaccinia and variola (smallpox) virus complement control proteins, which differ by only 11 aa, but differ 1000-fold in their ability to regulate complement activation, we investigated the role of electrostatic potential in predicting functional activity. Electrostatic modeling of the two proteins predicted that altering the vaccinia virus protein to contain the amino acids present in the second short consensus repeat domain of the smallpox protein would result in a vaccinia virus protein with increased complement regulatory activity. Mutagenesis of the vaccinia virus protein confirmed that changing the electrostatic potential of specific regions of the molecule influences its activity and identifies critical residues that result in enhanced function as measured by binding to C3b, inhibition of the alternative pathway of complement activation, and cofactor activity. In addition, we also demonstrate that despite the enhanced activity of the variola virus protein, its cofactor activity in the factor I-mediated degradation of C3b does not result in the cleavage of the alpha' chain of C3b between residues 954-955. Our data have important implications in our understanding of how regulators of complement activation interact with complement, the regulation of the innate immune system, and the rational design of potent complement inhibitors that might be used as therapeutic agents.
病原体和宿主对补体激活的调节对于生存至关重要。我们利用两种高度相关的正痘病毒蛋白，即痘苗病毒和天花病毒补体控制蛋白，它们仅相差11个氨基酸，但在调节补体激活的能力上相差1000倍，研究了静电势在预测功能活性中的作用。对这两种蛋白的静电建模预测，将痘苗病毒蛋白改变为含有天花蛋白第二个短共有重复结构域中的氨基酸，会产生一种补体调节活性增强的痘苗病毒蛋白。痘苗病毒蛋白的诱变证实，改变分子特定区域的静电势会影响其活性，并确定了通过与C3b结合、抑制补体激活的替代途径和辅因子活性来衡量的导致功能增强的关键残基。此外，我们还证明，尽管天花病毒蛋白的活性增强，但其在因子I介导的C3b降解中的辅因子活性并不会导致C3b的α'链在954 - 955位残基之间的裂解。我们的数据对于我们理解补体激活调节因子如何与补体相互作用、先天免疫系统的调节以及可能用作治疗剂的有效补体抑制剂的合理设计具有重要意义。
