Structural insights into the complex of trigger factor chaperone and ribosomal protein S7 from Mycobacterium tuberculosis.

Tuberculosis, caused by Mycobacterium tuberculosis (Mtb), has threaten human health for thousands years. The chaperone trigger factor (TF) of Mtb (mtbTF), a ribosome-associated molecule, plays important roles in co-translational nascent chain folding and post-translational protein assembly. However, due to lack of structural information, the dynamic regulatory mechanism of mtbTF remains barely investigated. Herein we report the structural basis of the complex of TF and ribosomal protein S7 (mtbS7) from Mtb. The mtbTF-mtbS7 complex was obtained with high purity and homogeneity in vitro. MtbTF bound with mtbS7 in a Kd value of 1.433 μM, and formed a complex with mtbS7 at 1:2 M ratios as shown by isothermal titration calorimetry. In addition, the crystal structure of mtbS7 was solved to a resolution at 1.8 Å, which was composed of six α-helices and two β-strands. Moreover, the molecular envelopes of mtbTF and mtbTF-mtbS7 complex were built and consisted with these homologous structures by small-angle X-ray scattering method. Our current findings might provide structural basis for understanding the molecular mechanism of TF in protein folding and the regulation of ribosomal assembly in Mtb.