1 Serum-mediated cleavage of Bacillus anthracis Protective Antigen is a two-step 1 process that involves a serum carboxypeptidase 2 3 4 5 David L. Goldman 1,2 *, Edward Nieves 3 , Antonio Nakouzi 1 , Johanna Rivera 1 , Ei Ei Phyu 2 , 6 Than Htut Win 2 , Jacqueline Achkar 1 and Arturo Casadevall 1,4 7 8 9 10 Departments of 1 Microbiology and Immunology, 2 Pediatrics, 3 Biochemistry, at the Albert 11 Einstein College of Medicine, Bronx, New York and the Children’s Hospital at Montefiore. 12 13 4 Present address: Department of Microbiology and Immunology, Johns Hopkins School of 14 Medicine, Baltimore, Maryland. 15 16 Key words: anthrax, lethal toxin, innate immunity, serum, protease 17 18 19 20 *Address all Correspondence to: 21 David L. Goldman 22 1300 Morris Park Ave 23 Bronx, NY 10461 24 Telephone: 718-741-2470 25 . CC-BY-NC-ND 4.0 International license not certified by peer review) is the author/funder. It is made available under a The copyright holder for this preprint (which was this version posted February 18, 2018. . https://doi.org/10.1101/267369 doi: bioRxiv preprint