Stewart P L, Chiu C Y, Huang S, Muir T, Zhao Y, Chait B, Mathias P, Nemerow G R
Department of Immunology, The Scripps Research Institute, La Jolla, CA, USA.
EMBO J. 1997 Mar 17;16(6):1189-98. doi: 10.1093/emboj/16.6.1189.
Interaction of the adenovirus penton base protein with alpha v integrins promotes virus entry into host cells. The location of the integrin binding sequence Arg-Gly-Asp (RGD) on human type 2 adenovirus (Ad2) was visualized by cryo-electron microscopy (cryo-EM) and image reconstruction using a mAb (DAV-1) which recognizes a linear epitope, IRGDTFATR. The sites for DAV-1 binding corresponded to the weak density above each of the five 22 A protrusions on the adenovirus penton base protein. Modeling of a Fab fragment crystal structure into the adenovirus-Fab cryo-EM density indicated a large amplitude of motion for the Fab and the RGD epitope. An unexpected finding was that Fab fragments, but not IgG antibody molecules, inhibited adenovirus infection. Steric hindrance from the adenovirus fiber and a few bound IgG molecules, as well as epitope mobility, most likely prevent binding of IgG antibodies to all five RGD sites on the penton base protein within the intact virus. These studies indicate that the structure of the adenovirus particle facilitates interaction with cell integrins, whilst restricting binding of potentially neutralizing antibodies.
腺病毒五聚体基底蛋白与αv整合素的相互作用促进病毒进入宿主细胞。通过冷冻电子显微镜（cryo-EM）和使用识别线性表位IRGDTFATR的单克隆抗体（DAV-1）进行图像重建，确定了人2型腺病毒（Ad2）上整合素结合序列精氨酸-甘氨酸-天冬氨酸（RGD）的位置。DAV-1结合位点对应于腺病毒五聚体基底蛋白上五个22埃突起中每个突起上方的低密度区域。将Fab片段晶体结构模型放入腺病毒-Fab冷冻电镜密度图中，结果表明Fab和RGD表位有较大的运动幅度。一个意外的发现是，Fab片段而非IgG抗体分子可抑制腺病毒感染。腺病毒纤维和一些结合的IgG分子产生的空间位阻以及表位的移动性，很可能阻止了IgG抗体与完整病毒内五聚体基底蛋白上所有五个RGD位点的结合。这些研究表明，腺病毒颗粒的结构有利于与细胞整合素相互作用，同时限制了潜在中和抗体的结合。
