Identification of nascent chain interaction sites on trigger factor

Area of Science:

• Molecular Biology
• Protein Folding
• Biochemistry

Background:

• The function of ribosome-binding molecular chaperones, like Trigger Factor (TF), in protein folding remains unclear.
• TF is the initial chaperone to engage with nascent polypeptides during bacterial translation.
• TF exhibits monomeric binding to ribosomes but dimerizes in solution, with distinct domain positioning.

Purpose of the Study:

• To elucidate the interaction sites and mechanisms of Trigger Factor (TF) with nascent polypeptide chains.
• To investigate the influence of TF's domain structure and dimerization on nascent chain binding.

Main Methods:

• Utilized site-specifically labeled TF proteins to map interactions with nascent chains during translation.
• Analyzed domain-specific interactions, including length-dependence and enzymatic activity independence.
• Compared nascent chain binding sites with TF dimer interface regions.

Main Results:

• All three domains of TF (N-terminal ribosome binding, C-terminal, and peptidyl-prolyl-cis/trans-isomerase (PPIase) domain) interact with nascent chains.
• PPIase domain interactions are length-dependent but not reliant on its isomerase activity.
• Dimerization of TF involves sites that also bind nascent chains, indicating partial occlusion of binding sites upon dimerization.

Conclusions:

• Nascent chains interact with TF via two main regions: the N-terminal and C-terminal domains (NC-domains) as the primary site, and the PPIase domain as an auxiliary site.
• TF's dimerization state influences its accessibility to nascent polypeptides, potentially modulating its chaperone function.
• These findings provide insights into the intricate mechanism of early protein folding mediated by TF.