Biology subjects

Kolli, D.

Publications and source records attributed to Kolli, D..

2 recordsLinked to original sources

bioRxiv2025

Transient binding facilitates super-resolution imaging of functional amyloid fibrils on living bacteria

Curli, which are the major proteinaceous component of the Escherichia coli biofilm extracellular matrix, help protect cells against environmental stressors including dehydration and antibiotics. Composed of the amyloid proteins CsgA and CsgB, curli self-assemble as these protomers are secreted into the extracellular space. The mechanisms of curli assembly and their functional roles within the extracellular matrix are incompletely understood. High-resolution imaging tools compatible with live-cell conditions provide a critical means to investigate the assembly and function of curli in their native context. In this study, we use super-resolution imaging to visualize curli fibrils on living bacterial cells. Transient amyloid binding of the fluorogenic dye Nile blue facilitates two complementary super-resolution fluorescence microscopy approaches: single-molecule localization microscopy and super-resolution optical fluctuation imaging. Additionally, imaging fluorescence correlation spectroscopy was used to measure the characteristic relaxation times associated with Nile blue binding to CsgA fibrils. Together, these approaches offer a framework for imaging-based biophysical characterization of curli structures on living cells. Importance/impact statementEscherichia coli and other enteric bacteria secrete amyloid proteins that self-assemble into fibrillar structures called curli, forming a key component of biofilm extracellular matrices. Bacterial biofilms confer resilience to harsh environments with broad implications for human health. In this study, we extend transient amyloid binding to the novel application of super-resolution fluorescence microscopy of curli on living cells, offering promising approaches to gain structural and mechanistic insights.

biophysics↗

bioRxiv2025

The bacterial chaperone CsgC inhibits functional amyloid CsgA formation by promoting the intrinsically disordered pre-nuclear state

E. coli assembles a functional amyloid called curli during biofilm formation. The major curlin subunit is the CsgA protein, which adopts a beta-sheet rich fold upon fibrillization. The chaperone-like protein CsgC inhibits CsgA amyloid formation. CsgA undergoes a 3-stage aggregation process: an initial lag phase where beta-rich nuclei form, an exponential elongation phase, and a plateau phase. It is currently not known if CsgC inhibits amyloid formation by inhibiting formation of a pre-fibril nucleus, or if CsgC inhibits a later stage of amyloid formation by blocking monomer addition. Here, CsgC homologs from C. youngae, C. davisae, and H. alvei were purified and characterized for their ability to interrogate CsgA amyloid formation. Each of the CsgC homologs prolonged the lag phase of E. coli CsgA amyloid formation similar to E. coli CsgC. Additionally, we found E. coli CsgC interacted transiently and weakly with a monomeric, pre-nucleus species of CsgA which delayed amyloid formation. A transient CsgC-CsgA heterodimer was observed using ion mobility-mass spectrometry. When CsgC was added to actively polymerizing CsgA, exponential growth commonly associated with nucleation-dependent amyloid formation was lost. Adding preformed CsgA seeds did not rescue exponential growth, indicating that CsgC also has inhibitory activity during fibril elongation. Indeed, CsgC interacted strongly with CsgA fibers, suggesting the interaction between CsgC and CsgA fibers can slow new fiber growth. CsgC displays unique inhibitory activity at multiple stages of amyloid formation. CsgC acts as an energy-independent chaperone that transiently interacts with prefibrillar CsgA and an amyloid fiber.

biochemistry↗