Visualizing Light-Driven Structural Dynamics in Myxobacterial Phytochromes Using Time-Resolved Cryo-EM
Location
SU-215
Start Date
1-5-2026 10:50 AM
Department
Chemistry
Abstract
Phytochromes are red and far-red light sensing photoreceptors that regulate light-dependent signaling in plants, fungi, and bacteria. While plant phytochromes have been extensively characterized, comparatively little is understood about phytochromes from non-pathogenic soil bacteria such as Stigmatella aurantiaca and Cystobacter fuscus, members of the myxobacteria. These organisms inhabit soil environments where far-red light penetrates more efficiently than shorter wavelengths, suggesting that far-red sensing may play an important ecological role in subsurface signaling and microbial-plant interactions. This thesis focuses on the purification, spectroscopic characterization, and crystallization of myxobacterial bacterial phytochromes to better understand their photoconversion mechanism and structural dynamics. Recombinant phytochrome proteins were expressed, purified, and reconstituted with biliverdin chromophore. Spectroscopy was used to confirm photoconversion between red-absorbing (Pr) and far-red-absorbing (Pfr) states and to assess chromophore incorporation and protein integrity. Crystallization trials were conducted under a range of conditions to promote formation of diffraction-quality crystals. Upon successful crystal formation, structural analysis proceeds via cryo-electron microscopy and complementary X-ray diffraction to determine high-resolution conformational changes associated with photoconversion. In cases where crystals are not obtained, additional optimization of crystallization parameters, including pH, precipitants, and protein concentration, is performed until successful. Understanding the structural basis of far-red light sensing in soil myxobacteria is significant because phytochrome signaling near plant root systems may influence microbial behavior, intercellular communication, and potentially plant growth responses. Recent findings demonstrating enhanced plant growth following introduction of myxobacteria into soil suggest that phytochrome-mediated response regulator pathways may contribute to beneficial root system interactions.
Faculty Sponsor
Emina Stojkovic
Visualizing Light-Driven Structural Dynamics in Myxobacterial Phytochromes Using Time-Resolved Cryo-EM
SU-215
Phytochromes are red and far-red light sensing photoreceptors that regulate light-dependent signaling in plants, fungi, and bacteria. While plant phytochromes have been extensively characterized, comparatively little is understood about phytochromes from non-pathogenic soil bacteria such as Stigmatella aurantiaca and Cystobacter fuscus, members of the myxobacteria. These organisms inhabit soil environments where far-red light penetrates more efficiently than shorter wavelengths, suggesting that far-red sensing may play an important ecological role in subsurface signaling and microbial-plant interactions. This thesis focuses on the purification, spectroscopic characterization, and crystallization of myxobacterial bacterial phytochromes to better understand their photoconversion mechanism and structural dynamics. Recombinant phytochrome proteins were expressed, purified, and reconstituted with biliverdin chromophore. Spectroscopy was used to confirm photoconversion between red-absorbing (Pr) and far-red-absorbing (Pfr) states and to assess chromophore incorporation and protein integrity. Crystallization trials were conducted under a range of conditions to promote formation of diffraction-quality crystals. Upon successful crystal formation, structural analysis proceeds via cryo-electron microscopy and complementary X-ray diffraction to determine high-resolution conformational changes associated with photoconversion. In cases where crystals are not obtained, additional optimization of crystallization parameters, including pH, precipitants, and protein concentration, is performed until successful. Understanding the structural basis of far-red light sensing in soil myxobacteria is significant because phytochrome signaling near plant root systems may influence microbial behavior, intercellular communication, and potentially plant growth responses. Recent findings demonstrating enhanced plant growth following introduction of myxobacteria into soil suggest that phytochrome-mediated response regulator pathways may contribute to beneficial root system interactions.