Biological Chemistry seminar: Gabriel Rosenblum, Weizmann Institute of Science

March 07, 2019 - 03:00 PM - 04:00 PM
Speaker: 

Gabriel Rosenblum

Department of Structural Biology

Weizmann Institute of Science

 

"Observation of Allosteric Signaling Through DNA with Single-Molecule FRET and Cryo-EM"


Gene networks often obey complex dynamics such as pulsing and oscillations that require a nearly binary “on” and ”off” switch in gene activity. At a molecular level, a high cooperativity in the interaction between transcription factors (TFs) and DNA is key for this switch. However, how this cooperativity is achieved is unknown for many systems. We used a combination of cryo-electron microscopy (cryo-EM) and single-molecule fluorescence spectroscopy to unravel the emergence of cooperativity in the interaction between ComK, a bacterial transcription factor from Bacillus subtilis, and its promoter sequence. The promoter contains two binding sites (AT-boxes) that are separated by 18 base pairs (6 nm). Single-molecule FRET experiments show a low cooperativity for the binding to individual AT-boxes whereas the combination of two distant binding sites in the natural promoter boosts cooperativity. Importantly, the boost does not result from interactions between ComK-molecules at the two sites, as revealed by a cryo-EM structure of the ComK-DNA complex. Instead, the results unravel a new allosteric mechanism. Cooperativity between the ComK-binding sites results from an axially transmitted signal through the DNA-structure. Hence, ComK-binding to one site increases the affinity of the 18 base pair distant site. This communication forms a toggle in which complete binding, i.e., the switch from “off” to “on”, is achieved within a narrow ComK concentration range.

 


Location: 

Carolyn Hoff Lynch Room

Chemistry Complex

 

Host:  Barry Cooperman

Department of Chemistry

231 S. 34 Street, Philadelphia, PA 19104-6323

215.898.8317 voice | 215.573.2112 fax | web@chem.upenn.edu