Single molecule studies of the bacterial curli protein CsgA reveal a structurally dynamic monomeric structure

Single Escherichia coli CsgA monomers probed by optical-tweezer force spectroscopy unfold and refold, revealing metastable folded states linked to partially folded and collapsed molten-globule conformations.

• Why it matters: Ensemble measurements and predictions disagree on whether monomeric CsgA is disordered or well folded, and its aggregation propensity has hindered direct structural characterization.
• What they did: The study used single-molecule force spectroscopy with optical tweezers on individual CsgA molecules, supported by steered molecular dynamics simulations to match unfolding patterns.
• The result: The observed unfolding/refolding behavior indicates equilibrium between metastable folded states and disordered states, implying aggregation-prone intermediates that may be missed in ensemble experiments.

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