Discovery of the Membrane Binding Domain in Trifunctional Proline Utilization A

Area of Science:

• Biochemistry
• Molecular Biology
• Microbiology

Background:

• Escherichia coli proline utilization A (EcPutA) is a trifunctional flavoprotein regulating proline utilization and catalyzing proline oxidation.
• EcPutA undergoes functional switching between transcriptional repression and enzymatic activity, dictated by flavin redox state.
• Understanding the membrane-binding domain is key to elucidating EcPutA's catalytic turnover and functional switching mechanism.

Purpose of the Study:

• To identify and characterize the membrane-binding domain of EcPutA.
• To investigate the role of the conserved C-terminal motif (CCM) in EcPutA membrane association and functional switching.
• To explore the involvement of the α-domain in EcPutA membrane binding.

Main Methods:

• Site-directed mutagenesis to delete or alter the CCM.
• Cell-based transcription assays to assess functional switching.
• Limited proteolysis to study conformational changes.
• Fluorescence resonance energy transfer (FRET) with dansyl-labeled liposomes to probe membrane interactions.

Main Results:

• Deletion or mutation of the CCM significantly impairs EcPutA's functional and physical association with membranes.
• The CCM is essential for EcPutA-mediated functional switching.
• Specific residues in the α-domain also contribute to membrane binding.
• The CCM and α-domain likely form a membrane-binding interface near the proline dehydrogenase (PRODH) domain.

Conclusions:

• The conserved C-terminal motif (CCM) is a critical determinant of EcPutA membrane binding.
• The CCM and α-domain cooperate to mediate EcPutA's interaction with the cellular membrane.
• This research provides insights into the structural basis of EcPutA functional switching and flavin redox signaling.