Structural Basis of Ca 2+ -Dependent Self-Processing Activity of Repeat-in-Toxin Proteins

Abstract

The Ca 2+ -dependent clip-and-link activity of large repeat-in-toxin (RTX) proteins is an exceptional posttranslational process in which an internal domain called a self-processing module (SPM) mediates Ca 2+ -dependent processing of a highly specific aspartate-proline (Asp-Pro) peptide bond and covalent linkage of the released aspartyl to an adjacent lysine residue through an isopeptide bond. Here, we report the solution structures of the Ca 2+ -loaded SPM (Ca-SPM) defining the mechanism of the autocatalytic cleavage of the Asp414-Pro415 peptide bond of the Neisseria meningitidis FrpC exoprotein. Moreover, deletion of the SPM domain in the ApxIVA protein, the FrpC homolog of Actinobacillus pleuropneumoniae , resulted in attenuation of virulence of the bacterium in a pig infection model, indicating that the Ca 2+ -dependent clip-and-link activity plays a role in the virulence of Gram-negative pathogens.