Single Residue Acts as Gate in OccK Channels

Area of Science:

• Structural biology
• Microbiology
• Biophysics

Background:

• The OccK protein subfamily in Pseudomonas aeruginosa forms dynamic outer membrane channels.
• These channels exhibit diverse conformational states, transitioning between open and closed forms.
• The specific molecular mechanisms governing OccK channel gating remained largely unknown.

Purpose of the Study:

• To elucidate the molecular determinants responsible for the diverse gating of OccK channels.
• To identify the specific residue and its role in mediating channel conformational changes.
• To understand the relationship between residue properties and channel function.

Main Methods:

• Molecular dynamics (MD) simulations were performed on the OccK5 (OpdH) channel.
• Site-directed mutagenesis was employed to alter the identified gate residue.
• Single-channel electrophysiology was used to measure the functional impact of mutations.

Main Results:

• MD simulations identified local fluctuations in loop L7, mediated by a single residue, as critical for gating.
• Mutagenesis and electrophysiology confirmed that this gate residue confers unique gating properties to OccK channels.
• Simulations revealed correlations between gate residue side-chain size, pore dimensions, and L7 loop flexibility.

Conclusions:

• A single residue in loop L7 acts as a crucial gate for OccK channels in Pseudomonas aeruginosa.
• The size of this residue's side-chain influences both pore size and loop flexibility, thereby controlling channel gating.
• This study provides a molecular basis for understanding the dynamic gating mechanisms of OccK outer membrane channels.