Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 7/18/2019
Publication Date: 7/18/2019
Citation: Naumann, T.A., Naldrett, M.J., Price, N.P. 2019. Kilbournase, a protease-associated domain subtilase secreted by the fungal corn pathogen Stenocarpella maydis [abstract].
Technical Abstract: The protease-associated (PA) domain is an accessory protein domain that is structurally separate from but encoded within the active site of some large subtilisin proteases. The most well-characterized PA domain subtilase is ScpA peptidase, a Streptococcal cell wall peptidase that truncates the human innate immunity protein C5a. PA domains are thought to give substrate specificity to subtilisins by capping the active site, restricting access and recruiting targeted proteins. Here we demonstrate that a protease secreted by the fungal corn pathogen Stenocarpella maydis, which truncates the corn ChitA protein, is a PA domain subtilase. Purified protease was isolated from S. maydis cultures and tryptic peptides were analyzed by LC-MS/MS. Observed peptide ions were mapped to two hypothetical PA domain subtilases encoded by the S. maydis genome. Yeast strains were created to express each candidate. One strain produced a protease that truncated ChitA. This protease was purified from yeast and its activity was characterized biochemically. It degraded the amino-terminal domain of corn ChitA, functioning as an exoprotease, while leaving the catalytic domain intact. It did not modify a homologous chitinase from the dicot plant Arabidopsis thaliana, indicating a high level of substrate specificity. The identified protein, that we name kilbournase, is only the second described subtilase that is an exoprotease. Truncation of corn ChitA by this pathogen PA domain subtilase, which resembles Streptococcal C5a protease, suggests ChitA may play a role in innate immunity.