Structure and function of A41, a vaccinia virus chemokine binding protein
Structure and function of A41, a vaccinia virus chemokine binding protein
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DOI：
10.1371/journal.ppat.0040005
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发表时间：
2008-01-01
期刊：
影响因子：
6.7
通讯作者：
Grimes, Jonathan M.
中科院分区：
文献类型：
--
作者：
Bahar, Mohammad W.;Kenyon, Julia C.;Grimes, Jonathan M.
牛痘病毒（VACV）A41 L基因编码一种分泌的30 kDa糖蛋白，该糖蛋白对病毒复制不是必需的，但影响宿主对感染的反应。A41蛋白与另一种结合CC趋化因子的VACV蛋白（称为vCKBP，或病毒CC趋化因子抑制剂，vCCI）共享序列相似性，并且缺乏A41 L基因的VACV菌株诱导的CD 8（+）T细胞应答比表达A41的对照病毒更强。使用表面等离子体共振，我们筛选了39种人类和小鼠趋化因子，并将CCL 21，CCL 25，CCL 26和CCL 28鉴定为A41配体，K（d）在8 nM和118 nM之间。尽管如此，A41在抑制这些趋化因子诱导的趋化性方面是无效的，表明它没有阻断这些趋化因子与其受体的相互作用。然而，A41和趋化因子的相互作用被肝素以剂量依赖性方式抑制，表明A41和肝素结合到这些趋化因子上的重叠位点。为了更好地理解A41的作用机制，将其晶体结构解析到1.9埃分辨率。该蛋白具有类似于痘病毒vCCI蛋白家族的球状β夹心结构，但存在显著的结构差异，特别是在表面环和静电电荷分布方面。结构建模表明，为vCCI-趋化因子相互作用定义的结合范例可能在A41及其趋化因子伙伴之间是保守的。此外，结合A41的趋化因子的序列分析鉴定了A41结合的特征。生物学和结构数据表明，A41通过与某些趋化因子形成中等强度（nM）的相互作用来发挥作用，足以干扰细胞表面的趋化因子-糖胺聚糖相互作用（μ M-nM），从而破坏趋化因子浓度梯度，但不足以破坏（pM）趋化因子-趋化因子受体相互作用。
The vaccinia virus (VACV) A41L gene encodes a secreted 30 kDa glycoprotein that is nonessential for virus replication but affects the host response to infection. The A41 protein shares sequence similarity with another VACV protein that binds CC chemokines (called vCKBP, or viral CC chemokine inhibitor, vCCI), and strains of VACV lacking the A41L gene induced stronger CD8(+) T-cell responses than control viruses expressing A41. Using surface plasmon resonance, we screened 39 human and murine chemokines and identified CCL21, CCL25, CCL26 and CCL28 as A41 ligands, with K(d)s of between 8 nM and 118 nM. Nonetheless, A41 was ineffective at inhibiting chemotaxis induced by these chemokines, indicating it did not block the interaction of these chemokines with their receptors. However the interaction of A41 and chemokines was inhibited in a dose-dependent manner by heparin, suggesting that A41 and heparin bind to overlapping sites on these chemokines. To better understand the mechanism of action of A41 its crystal structure was solved to 1.9 angstrom resolution. The protein has a globular beta sandwich structure similar to that of the poxvirus vCCI family of proteins, but there are notable structural differences, particularly in surface loops and electrostatic charge distribution. Structural modelling suggests that the binding paradigm as defined for the vCCI-chemokine interaction is likely to be conserved between A41 and its chemokine partners. Additionally, sequence analysis of chemokines binding to A41 identified a signature for A41 binding. The biological and structural data suggest that A41 functions by forming moderately strong (nM) interactions with certain chemokines, sufficient to interfere with chemokine-glycosaminoglycan interactions at the cell surface (mu M-nM) and thereby to destroy the chemokine concentration gradient, but not strong enough to disrupt the (pM) chemokine-chemokine receptor interactions.