Anaplasma phagocytophilum, the aetiologic agent of human granulocytic anaplasmosis (HGA) is an obligate intracellular Gram-negative bacterium. During intracellular replication, A. phagocytophilum interacts with many host cell components including actin cytoskeleton. However the bacterial factors contributing to the interaction between A. phagocytophilum and actin filaments remain unknown. In this study we identified a novel type IV secretion system substrate of A. phagocytophilum by employing TEM-1 β-lactamase based protein translocation assay, and found it is an actin filament-associated protein. Here, we name this protein as an actin filament-associated Anaplasma phagocytophilum protein (AFAP). Further analysis showed that the middle region of AFAP harboring four tandem repeats is involved in its interaction with actin filaments. The identification and characterization of an actin filament-associated A. phagocytophilum protein in this study may help understand the interaction between A. phagocytophilum and actin cytoskeleton of its host cells, facilitating the elucidation of HGA pathogenesis.

嗜人粒细胞无胞浆菌是人类粒细胞无形体病（HGA）的病原体，是专性的细胞内革兰氏阴性细菌。在细胞内复制过程中，吞噬链球菌与许多宿主细胞成分（包括肌动蛋白细胞骨架）相互作用。然而，尚不清楚导致吞噬嗜酸曲霉和肌动蛋白丝之间相互作用的细菌因素。在这项研究中，我们通过使用基于TEM-1β-内酰胺酶的蛋白移位测定法，鉴定了一种新的吞噬嗜血曲霉IV型分泌系统底物，并发现它是肌动蛋白丝相关蛋白。在这里，我们命名此蛋白质作为一个一个已将˚F ilament-相关的一个naplasma吞噬细胞 p rotein（AFAP）。进一步的分析表明，具有四个串联重复序列的AFAP的中间区域参与了它与肌动蛋白丝的相互作用。在这项研究中肌动蛋白丝相关的噬菌嗜性链球菌蛋白的鉴定和表征可能有助于理解嗜噬菌嗜性粒细胞及其宿主细胞的肌动蛋白细胞骨架之间的相互作用，从而有助于阐明HGA的发病机理。