Bacterial Chaperone Domain Insertions Convert Human FKBP12 into an Excellent Protein-Folding Catalyst—A Structural and Functional Analysis

TL;DR

Adding bacterial chaperone domains to human FKBP12 significantly boosts its ability to help proteins fold correctly.

Contribution

Inserting chaperone domains from bacteria into FKBP12 enhances its folding activity and structural stability.

Findings

Chaperone domain insertions from E. coli and Thermococcus sp. increased FKBP12's folding activity.

Crystal structures showed the inserted domains did not disrupt FKBP12's or their own structures.

The domain orientations suggest a mechanism for transferring substrate proteins between domains.

Abstract

Many folding enzymes use separate domains for the binding of substrate proteins and for the catalysis of slow folding reactions such as prolyl isomerization. FKBP12 is a small prolyl isomerase without a chaperone domain. Its folding activity is low, but it could be increased by inserting the chaperone domain from the homolog SlyD of E. coli near the prolyl isomerase active site. We inserted two other chaperone domains into human FKBP12: the chaperone domain of SlpA from E. coli, and the chaperone domain of SlyD from Thermococcus sp. Both stabilized FKBP12 and greatly increased its folding activity. The insertion of these chaperone domains had no influence on the FKBP12 and the chaperone domain structure, as revealed by two crystal structures of the chimeric proteins. The relative domain orientations differ in the two crystal structures, presumably representing snapshots of a more open and a more closed conformation. Together with crystal structures from SlyD-like proteins, they suggest a path for how substrate proteins might be transferred from the chaperone domain to the prolyl isomerase domain.

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