The SFB 1078 kindly invites you to the following colloquium talks:

1. Dr. David Buhrke hosted by Prof. Franz Bartl (HUB):

Title: Understanding the Cyanobacteriochrome Slr-g3 with advanced IR spectroscopy

Red/green cyanobacteriochromes like Slr-g3 bind open-chain tetrapyrroles as light-sensitive chromophores and are closely related to phytochromes. They can be photo-switched between a red-absorbing (Pr) and green-absorbing (Pg) form in a bistable and reversible manner. In my talk I will discuss how the molecular details of this photoswitching process can be understood by applying advanced IR spectroscopic methods. We applied time resolved linear and 2D IR spectroscopy to track the sequence of photocycle intermediates over many orders in magnitude in time, from the excited state decay in picoseconds to the formation of the final photoproduct in miliseconds. In the conversion from Pg to Pr form we have revealed new intermediates which precedes the Pr formation. In addition, stationary and transient 2D IR experiments measured the vibrational couplings between different groups of the chromophore among each other and with the protein. Finally, anharmonic QM/MM calculations are shown to be in good agreement with experimental 2D IR spectra of the initial and the final state of the photocycle and explain the coupling pattern.

2. Prof. Marilyn Gunner:

Title: How the multiplicity of protonation states in proteins supports proton transfers

Proteins are known to exist in a distribution of conformations, but the distribution of protonation states in the equilibrium ensemble is under appreciated. Recent developments in the MCCE program have enabled the analysis of protonation and conformation microstates in Monte Carlo sampling, providing insights into the diverse protonation states that exist in proteins.

Proton pumps contain proton loading sites, which undergo significant changes in proton affinity (>5 pH unit shifts) to cycle through proton-bound and released states in their reaction cycle. In this discussion, I will explore how clusters of amino acids, with multiple possible protonation states, facilitate efficient proton pumping. I will also describe how Proton Loading Sites that are made up of clusters of amino acids are often embedded in complex proton transfer networks. 

Thanks to Junjun Mao (CCNY) and Umesh Khaniya (NIH).