Dynamic interplay of membrane‐proximal POTRA domain and conserved loop L 6 in O mp85 transporter FhaC

• Published in: Molecular microbiology Vol. 98; no. 3; pp. 490 - 501
• Main Authors: Guérin, Jeremy, Saint, Nathalie, Baud, Catherine, Meli, Albano C., Etienne, Emilien, Locht, Camille, Vezin, Hervé, Jacob‐Dubuisson, Françoise
• Format: Journal Article
• Language: English
• Published: 01-10-2015
• ISSN: 0950-382X; 1365-2958
• DOI: 10.1111/mmi.13137

Omp85 transporters mediate protein insertion into, or translocation across, membranes. They have a conserved architecture, with
POTRA
domains that interact with substrate proteins, a 16‐stranded transmembrane β barrel, and an extracellular loop,
L
6, folded back in the barrel pore. Here using electrophysiology,
in vivo
biochemical approaches and electron paramagnetic resonance, we show that the
L
6 loop of the
O
mp85 transporter
FhaC
changes conformation and modulates channel opening. Those conformational changes involve breaking the conserved interaction between the tip of
L
6 and the inner β‐barrel wall. The membrane‐proximal
POTRA
domain also exchanges between several conformations, and the binding of
FHA
displaces this equilibrium. We further demonstrate a dynamic, physical communication between the
POTRA
domains and
L
6, which must take place
via
the β barrel. Our findings thus link all three essential components of
O
mp85 transporters and indicate that they operate in a concerted fashion in the transport cycle.