Functional elucidation of TfuA in peptide backbone thioamidation

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• YcaO enzymes perform post-translational thioamidation, replacing amide oxygen with sulfur.
• TfuA proteins are often found near YcaO enzymes and are required for thioamidation.
• The specific role of TfuA in this process remained unclear.

Purpose of the Study:

• To elucidate the function of TfuA in methyl-coenzyme M reductase thioamidation.
• To characterize the interaction between TfuA, YcaO, and the sulfur donor ThiS.
• To determine the structural basis for TfuA's activity.

Main Methods:

• Biochemical assays to test TfuA's enzymatic activity.
• Protein-protein interaction studies between TfuA, YcaO, and ThiS.
• X-ray crystallography to determine the structure of TfuA.
• Site-directed mutagenesis to probe the active site and binding interfaces.

Main Results:

• TfuA hydrolyzes thiocarboxylated ThiS (ThiS-COSH), a proteinaceous sulfur donor.
• TfuA enhances the binding affinity of YcaO to its thioamidation substrate.
• A novel protein fold for TfuA was determined by X-ray crystallography.
• Conserved binding interfaces between TfuA, YcaO, and ThiS were identified.
• A hydrolase-like active site with a Ser-Lys catalytic dyad was revealed in TfuA.

Conclusions:

• TfuA plays a critical role in thioamidation by processing the sulfur donor and facilitating YcaO activity.
• The structural and biochemical data provide a mechanistic understanding of TfuA's function.
• TfuA represents a new class of enzyme involved in post-translational modifications.