Characterization of FimC, a periplasmic assembly factor for biogenesis of type 1 pili in Escherichia coli

Assembly of type 1 pill from Escherichia coli is mediated by FimC, a peripl asmic chaperone (assembly factor) consisting of two immunoglobulin-like dom ains. FimC is assumed to recognize the individual pilus subunits in the per iplasm mainly via their conserved C-terminal segments and to deliver the:su bunits to an assembly platform in the outer membrane. Here we present the f irst biochemical characterization of a periplasmic pilus chaperone and anal yze the importance of the two chaperone domains for stability and function. Comparison of the isolated C-terminal domain with wild-type FimC revealed a strongly reduced thermodynamic stability, indicating strong interdomain i nteractions. The affinity of FimC toward a peptide corresponding to the 11 C-terminal residues of the type 1 pilus adhesin FimH is at least 1000-fold lower compared to binding of intact FimH, confirming that bacterial pilus c haperones, unlike other chaperones, specifically interact with folded pilus subunits.