TrkA undergoes a tetramer-to-dimer conversion to open TrkH which enables changes in membrane potential

Area of Science:

• Bacterial ion transport
• Molecular mechanisms of channel gating
• Cellular energetics

Background:

• TrkH is a bacterial potassium channel essential for K+ uptake and pH homeostasis.
• TrkA regulates TrkH channel activity, with ADP inducing closure and ATP inducing opening.
• The precise mechanism by which nucleotides control TrkH gating via TrkA remains elusive.

Purpose of the Study:

• To elucidate the structural basis of nucleotide-dependent TrkH channel gating.
• To understand how TrkA's conformational changes regulate TrkH activity.
• To investigate the physiological role of the TrkH-TrkA complex in cellular potential.

Main Methods:

• X-ray crystallography to determine the structures of the TrkH-TrkA complex in the presence of ADP and ATP.
• Biochemical assays to assess the functional requirements for channel gating.
• Genetic manipulation of Escherichia coli to study the physiological impact of TrkA deletion.

Main Results:

• TrkA forms a closed tetrameric ring with TrkH in the presence of ADP, constraining the channel.
• TrkA dissociates into dimers upon ATP binding, releasing constraints and opening the TrkH channel.
• Both TrkA's conformational change and the release of constraints on TrkH are critical for channel gating.
• TrkA deletion in E. coli leads to cell depolarization, indicating TrkH-TrkA's role in coupling nucleotide levels to membrane potential.

Conclusions:

• The study reveals the atomic structures of the TrkH-TrkA complex, detailing nucleotide-mediated gating.
• TrkA's tetramer-to-dimer transition is the key mechanism for controlling TrkH channel activity.
• The TrkH-TrkA complex plays a vital role in maintaining bacterial membrane potential by sensing intracellular nucleotide levels.