Anaplasma phagocytophilum Ats-1 Is imported into host cell mitochondria and interferes with apoptosis induction

Anaplasma phagocytophilum,the causative agent of human granulocytic anaplasmosis,infects human neutrophils and inhibits mitochondria-mediated apoptosis. bacterial factors involved in this process are unknown. in the present study,we screened a genomic dna library of a. phagocytophilum for effectors of the type iv secretion system by a bacterial two-hybrid system,using a. phagocytophilum vird4 as bait. a hypothetical protein was identified as a putative effector,hereby named anaplasma translocated substrate 1 (ats-1). using triple immunofluorescence labeling and western blot analysis of infected cells,including human neutrophils,we determined that ats-1 is abundantly expressed by a. phagocytophilum,translocated across the inclusion membrane,localized in the host cell mitochondria,and cleaved. ectopically expressed ats-1 targeted mitochondria in an n-terminal 17 residue-dependent manner,localized in matrix or at the inner membrane,and was cleaved as native protein,which required residues 55-57. in vitro-translated ats-1 was imported in a receptordependent manner into isolated mitochondria. ats-1 inhibited etoposide-induced cytochrome c release from mitochondria,parp cleavage,and apoptosis in mammalian cells,as well as bax-induced yeast apoptosis. ats-1(55-57) had significantly reduced anti-apoptotic activity. bax redistribution was inhibited in both etoposide-induced and bax-induced apoptosis by ats-1. taken together,ats-1 is the first example of a bacterial protein that traverses five membranes and prevents apoptosis at the mitochondria. © 2010 niu et al.