Functional identification of a FKBP-like protein involved in the folding of overproduced secreted proteins.

Some bacterial peptidyl-prolyl isomerases (PPIases) are involved in secretory protein folding after the translocation step. has been used as a host for engineering extracellular overproduction of homologous and heterologous proteins in industrial applications. Although the mechanisms governing the major secretory pathway (Sec route) and the minor secretory pathway (Tat route) are reasonably well described, the function of proteins responsible for the extracellular secretory protein folding is not characterized as yet. We have characterized a Tat-dependent S FK506-binding protein-like lipoprotein (FKBP) that has PPIase activity. A mutant in the gene induces a secretion stress response and affects secretion and activity of the Sec-dependent protein α-amylase. Additionally, propagation in high copy number of the gene has a positive effect on the activity of both the overproduced α-amylase and the overproduced Tat-dependent agarase, both containing proline isomers. Targeted proteomic analyses showed that a relevant group of secreted proteins in TK21 are affected by Sli-FKBP, revealing a wide substrate range. The results obtained indicate that, regardless of the secretory route used by proteins in , adjusting the expression of may facilitate folding of dependent proteins when engineering strains for the overproduction of homologous or heterologous secretory proteins.