A PEROXIDASE RELATED TO THE MAMMALIAN ANTIMICROBIAL PROTEIN MYELOPEROXIDASE IN THE EUPRYMNA-VIBRIO MUTUALISM

Many animal-bacteria cooperative associations occur in highly modified host organs that create a unique environment for housing and maintain ing the symbionts, It has been assumed that these specialized organs d evelop through a program of symbiosis-specific or -enhanced gene expre ssion in one or both partners, but a clear example of this process has been lacking, In this study, we provide evidence for the enhanced pro duction of an enzyme! in the symbiotic organ of the squid Euprymna sco lopes, which harbors a culture of the luminous bacterium Vibrio fische ri, Our data show that this enzyme has a striking biochemical similari ty to mammalian myeloperoxidase (MPO; EC 1.11.17), an antimicrobial di anisidine peroxidase that occurs in neutrophils. MPO and the squid per oxidase catalyze the same reaction, have similar apparent subunit mole cular masses, and a polyclonal antibody to native human MPO specifical ly localized a peroxidase-like protein to the bacteria-containing regi ons of the symbiotic organ, We also provide evidence that a previously described squid cDNA encodes the protein (LO4) that is responsible fo r the observed dianisidine peroxidase activity. An antibody made again st a fragment of LO4 immunoprecipitated dianisidine peroxidase activit y from extracts of the symbiotic organ, and reacted against these extr acts and human MPO in Western blot analysis. These data suggest that r elated biochemical mechanisms for the control of bacterial number and growth operate in associations that are as functionally diverse as pat hogenesis and mutualism, and as phylogenetically distant as molluscs a nd mammals.