Thrombocidins, microbicidal proteins from human flood platelets, are C-terminal deletion products of CXC chemokines

Antibacterial proteins are components of the innate immune system found in many organisms and produced by a variety of cell types. Human blood platele ts contain a number of antibacterial proteins in their cu-granules that are released upon thrombin activation. The present study was designed to purif y these proteins obtained from human platelets and to characterize them che mically and biologically. Two antibacterial proteins were purified from pla telet granules in a two-step protocol using cation exchange chromatography and continuous acid urea polyacrylamide gel electrophoresis and were design ated thrombocidin (TC)-1 and TC-2, Characterization of these proteins using mass spectrometry and N-terminal sequencing revealed that TC-1 and TC-2 ar e variants of the CXC chemokines neutrophil-activating peptide-2 and connec tive tissue-activating peptide-III, respectively. TC-1 and TC-2 differ from these chemokines by a C-terminal truncation of 2 amino acids. Both TCs, bu t not neutrophil-activating peptide-2 and connective tissue-activating pept ide-III, were bactericidal for Bacillus subtilis, Escherichia coli, Staphyl ococcus aureus, and Lactococcus lactis and fungicidal for Cryptococcus neof ormans. Killing of B. subtilis by either TC appeared to be very rapid. Beca use TCs were unable to dissipate the membrane potential of L. lactis, the m echanism of TC-mediated killing most probably does not involve pore formati on.