Liszewski M Kathryn, Leung Marilyn K, Hauhart Richard, Fang Celia J, Bertram Paula, Atkinson John P
Department of Medicine, Division of Rheumatology, Washington University School of Medicine, St. Louis, MO 63110, USA.
J Immunol. 2009 Sep 1;183(5):3150-9. doi: 10.4049/jimmunol.0901366. Epub 2009 Aug 10.
Although smallpox was eradicated as a global illness more than 30 years ago, variola virus and other related pathogenic poxviruses, such as monkeypox, remain potential bioterrorist weapons or could re-emerge as natural infections. Poxviruses express virulence factors that down-modulate the host's immune system. We previously compared functional profiles of the poxviral complement inhibitors of smallpox, vaccinia, and monkeypox known as SPICE, VCP (or VICE), and MOPICE, respectively. SPICE was the most potent regulator of human complement and attached to cells via glycosaminoglycans. The major goals of the present study were to further characterize the complement regulatory and heparin binding sites of SPICE and to evaluate a mAb that abrogates its function. Using substitution mutagenesis, we established that (1) elimination of the three heparin binding sites severely decreases but does not eliminate glycosaminoglycan binding, (2) there is a hierarchy of activity for heparin binding among the three sites, and (3) complement regulatory sites overlap with each of the three heparin binding motifs. By creating chimeras with interchanges of SPICE and VCP residues, a combination of two SPICE amino acids (H77 plus K120) enhances VCP activity approximately 200-fold. Also, SPICE residue L131 is critical for both complement regulatory function and accounts for the electrophoretic differences between SPICE and VCP. An evolutionary history for these structure-function adaptations of SPICE is proposed. Finally, we identified and characterized a mAb that inhibits the complement regulatory activity of SPICE, MOPICE, and VCP and thus could be used as a therapeutic agent.
尽管天花作为一种全球性疾病在30多年前就已被根除，但天花病毒和其他相关的致病性痘病毒，如猴痘病毒，仍然是潜在的生物恐怖主义武器，或者可能作为自然感染重新出现。痘病毒表达下调宿主免疫系统的毒力因子。我们之前分别比较了天花、牛痘和猴痘的痘病毒补体抑制剂的功能概况，它们分别被称为SPICE、VCP（或VICE）和MOPICE。SPICE是人类补体最有效的调节剂，并通过糖胺聚糖附着于细胞。本研究的主要目标是进一步表征SPICE的补体调节和肝素结合位点，并评估一种消除其功能的单克隆抗体。通过取代诱变，我们确定：（1）消除三个肝素结合位点会严重降低但不会消除糖胺聚糖结合；（2）三个位点之间肝素结合存在活性层次；（3）补体调节位点与三个肝素结合基序中的每一个重叠。通过创建SPICE和VCP残基互换的嵌合体，两个SPICE氨基酸（H77加K120）的组合使VCP活性提高了约200倍。此外，SPICE残基L131对补体调节功能至关重要，并解释了SPICE和VCP之间的电泳差异。本文提出了SPICE这些结构-功能适应性的进化史。最后，我们鉴定并表征了一种抑制SPICE、MOPICE和VCP补体调节活性的单克隆抗体，因此它可用作治疗剂。
