Localization and accessibility of antigenic sites of the extracellular serine proteinase of Lactococcus lactis.

Lactococcus lactis strains produce an extracellular subtilisin-related serine proteinase in which immunologically different components can be distinguished. Monoclonal antibodies specific for the different proteinase components have been raised and their epitopes were identified. By Western-blot analysis it was found that all monoclonal antibodies recognize all denatured proteinase components. The distinction between the different components could be made under native conditions only, indicating that binding regions are masked in the native molecule. In a L. lactis proteinase which was inactivated by the substitution Asp30----Asn under native conditions, only one epitope could be detected. This demonstrates that autoproteolytic activity is required to make specific binding regions accessible for (monoclonal) antibodies.