Inter-domain dynamics in the chaperone SurA and multi-site binding to its outer membrane protein clients

Area of Science:

• Microbiology
• Structural Biology
• Biochemistry

Background:

• The periplasmic chaperone SurA is essential for bacterial outer membrane protein (OMP) biogenesis.
• The precise mechanisms of SurA's client binding and chaperone activity remain incompletely understood.
• E. coli SurA possesses a core domain and two peptidylprolyl isomerase domains (P1 and P2).

Purpose of the Study:

• To elucidate the client binding sites on SurA.
• To investigate the role of conformational dynamics in OMP recognition by SurA.
• To understand the functional implications of SurA's structural flexibility in OMP biogenesis.

Main Methods:

• Chemical cross-linking
• Hydrogen-deuterium exchange mass spectrometry (HDX-MS)
• Single-molecule Förster Resonance Energy Transfer (smFRET)
• Molecular dynamics (MD) simulations

Main Results:

• SurA exists in an array of conformations in solution, with the P2 domain often positioned closer to the core/P1 domains than previously modeled.
• OMP binding sites are predominantly located within the SurA core domain.
• OMP binding induces significant conformational changes involving the core and P1 domains of SurA.

Conclusions:

• Unfolded OMP substrates likely bind within a 'cradle' formed by the SurA domains.
• SurA's inherent structural flexibility facilitates OMP recognition, binding, and subsequent release.
• These findings provide critical insights into the molecular mechanisms governing bacterial OMP biogenesis.