This seminar will only be available remotely.
VIEW THIS SEMINAR LIVE VIA THE WEB AT:
https://zoom.us/j/4165865928

Uthama Edupuganti, Ph.D. student, Kevin Gardner group, CUNY ASRC, will give a talk on "Structural and functional insights to allosteric regulation of blue light sensing by LOV domains."

ABSTRACT    Photoreceptors play a crucial role in signal transduction by modulating the process at molecular level via sensing light as environmental stimuli and transducing this signal to downstream functions. One class of photoreceptors, the Light-Oxygen-Voltage (LOV) domains, sense blue light in plants, bacteria, and algal systems. Since initial discovery, details of their photochemistry, chromophore interactions and use with diverse functional effectors have been described. However, several key details of their signaling mechanism and regulation are still poorly understood, limited in part by the need for structural insights of active states of full-length systems. Here, I fill this gap in knowledge by examining EL222 – a bacterial blue-light activate transcription factor – as a model LOV protein and determine the structures of active states and mutating the residues at the structural and functional interfaces. Upon illumination, the photochemistry of internally bound flavin cofactor triggers the intra and interdomain rearrangements leading up to effector release and DNA binding. While dark state structure is known from X-ray crystallography, the heterogeneity and dynamics of active state and size of the DNA-bound complex required an integrative structural biology approach of several techniques including EPR, HDX-MS, and NMR. By combining their output, including EPR distance constraints, HDX-MS global and local peptide level dynamics, and NMR chemical shift perturbations, I obtained a wealth of information to model EL222 active states. Complementary studies of point mutants at domain interfaces let me test our understanding of the allosteric determinants of effector release and signal propagation. Taken together, these results will assist in engineering new optogenetic systems and/or fine-tuning these exciting systems.

Binod Nepal, Postdoctoral Associate, Themis Lazaridis group, City College of New York, will give a talk on "Mechanism of negative membrane curvature generation by ESCRTIII subunit Snf7 and I-BAR domains."

ABSTRACT    Membrane remodeling is essential in key cellular events, such as endocytosis (positive curvature towards the cytoplasm) and viral budding (negative curvature towards the cytoplasm). We used an implicit membrane model to explore the mechanism of two important negative curvature sensing and generating proteins: the main ESCRT III subunit Snf7 and IRSP53 I-BAR domain. We observed spontaneous bending of Snf7 oligomers into circular structures with preferred radius of ~20 nm. Snf7 filaments cannot bind with the same interface to flat and curved membranes. We found that even when a filament has the preferred radius, it is always less stable on the flat membrane surface than on the interior cylindrical membrane surface. This could provide the required energy for membrane bending.  The IRSP53 I-BAR domain dimer is another protein that senses and generates negative membrane curvature by an unknown mechanism. We studied possible oligomeric structures of this protein that may be responsible for negative curvature generation. Our results show that I-BAR dimers undergo lateral and end-to-end interactions to form higher oligomers which are more curvature sensing than the individual dimers. The lateral interaction tends to give an oligomer shape with a convex membrane binding interface, which is consistent with negative curvature generation.