Hussain Mohammad A, Siedlecki Christopher A
Department of Surgery, The Biomedical Engineering Institute, The Milton S. Hershey Medical Center, The Pennsylvania State University, Hershey PA 17033, USA.
Micron. 2004;35(7):565-73. doi: 10.1016/j.micron.2004.02.010.
The platelet membrane receptor alpha(IIb) beta(3) binds to adsorbed protein ligands including fibrinogen, von Willebrand factor and fibronectin, and is critically important in mediating platelet adhesion to damaged subendothelium and to synthetic biomaterial surfaces. This receptor is a member of the integrin family, a highly prevalent class of heterodimeric molecules consisting of a single alpha and beta subunit. In an ongoing effort to understand the mechanisms underlying platelet adhesion events, high-resolution atomic force microscopy (AFM) under dynamic conditions was used to obtain images of alpha(IIb) beta(3) molecules as well as aggregates of the protein. Images of integrin molecules were obtained by tapping mode AFM under aqueous buffer conditions following adsorption on a series of ultrasmooth model surfaces. On a model hydrophobic surface, detergents stabilizing the protein in solution competed for surface adsorption sites. When this detergent was removed from the system, the protein was predominantly seen as aggregates with head groups pointing outward. A limited number of individual integrin molecules were observed, and were found to have dimensions consistent with those reported previously by electron microscopy studies. Integrin molecules showed weak adhesion to the two hydrophilic surfaces used in the study, although formation of a lipid bilayer around surface-adsorbed molecules improved the resolution. At longer time periods, the integrin molecules embedded in this lipid bilayer exhibited sufficient mobility to form molecular aggregates. The structural measurements described in this study not only reveal three-dimensional features of the molecule, they represent an important step towards dynamic adsorption experiments and visualizing the integrin interacting with surface-adsorbed proteins as in biomaterial-induced thrombogenesis.
血小板膜受体α(IIb)β(3)与包括纤维蛋白原、血管性血友病因子和纤连蛋白在内的吸附蛋白配体结合，在介导血小板黏附于受损的内皮下层及合成生物材料表面方面至关重要。该受体是整合素家族的成员，整合素家族是一类高度普遍的异二聚体分子，由单个α亚基和β亚基组成。为持续深入了解血小板黏附事件的潜在机制，在动态条件下使用高分辨率原子力显微镜(AFM)获取α(IIb)β(3)分子以及该蛋白聚集体的图像。在一系列超光滑模型表面吸附后，通过在水缓冲条件下的轻敲模式AFM获得整合素分子的图像。在一个模型疏水表面上，稳定溶液中蛋白质的去污剂竞争表面吸附位点。当从系统中去除这种去污剂时，蛋白质主要呈现为头基团向外的聚集体。观察到数量有限的单个整合素分子，发现其尺寸与先前电子显微镜研究报道的一致。整合素分子对研究中使用的两个亲水表面显示出较弱的黏附力，尽管在表面吸附分子周围形成脂质双层可提高分辨率。在较长时间段内，嵌入该脂质双层的整合素分子表现出足够的流动性以形成分子聚集体。本研究中描述的结构测量不仅揭示了该分子的三维特征，它们还代表了朝着动态吸附实验以及可视化整合素与生物材料诱导血栓形成过程中表面吸附蛋白相互作用迈出的重要一步。
