Interaction of the Bacillus subtilis chaperone CsaA with the secretory protein YvaY

Bacillus subtilis CsaA was previously characterised as a molecular chaperone with export-related activities. In order to elucidate the functionality of CsaA further, interaction with its postulated substrate YvaY was investigated. Similar binding to carrier immobilised mature and preYvaY revealed that the interaction was not mediated via the signal peptide of preYvaY. Higher affinity to denatured peptides compared to native peptides indicated preferred binding to unfolded proteins. To characterise affinity of CsaA more detailed, binding to preYvaY derived peptides was analysed. CsaA showed affinity to multiple peptides in the scan, mainly correlated to a positive net charge. Affinity of export-specific Escherichia coli chaperone SecB to the carrier immobilised peptides indicated partially overlapping binding characteristics of SecB and CsaA.