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

Prof. Minhaeng Cho 

Department of Chemistry, Korea University, KR

Title: Time-resolved IR spectroscopic study of water structure and dynamics in biological systems

Abstract:

In the realm of cellular biology, the relationship between the cytomatrix and intracellular water is a subject of intense scrutiny. The concept that the cytomatrix and cell water should be regarded as an intricate system akin to a super-complex material and a few challenges against traditional notions of water within the cell are briefly mentioned. Central to the long-standing scientific debates is the intriguing divergence between the dynamics and properties of intracellular water and those of pure liquid water.

Water, often referred to as life's "mother and medium" by Szent-Györgyi, plays a pivotal role in shaping the structure and function of biological macromolecules. Internal conserved water, through hydrogen bonding, contributes to protein conformation, while surface-conserved water molecules are involved in conformational changes that regulate their functions. Over the past decades, a gap has persisted between the perspectives of two groups of scientists concerning the structure and dynamics of intracellular water, underscoring the need for a unified approach. Primarily, the influence of water's structural organization extends beyond the molecular scale, affecting the motional properties of the aqueous matrix. Key questions revolve around the direct relationship between dynamic aspects of water - translational and rotational diffusion processes, hydrogen-bond formation and breakage rates - and water's structural arrangement.

To illustrate these concepts, I will present two case studies. First, we explore spatially confined water in reverse micelles and on membrane surfaces. The second case study examines protein aggregations in both H₂O and D₂O environments, where we employed techniques such as time-resolved IR spectroscopy, MD simulations, and various methods, revealing water's structural intricacies within these confined and controlled environments.

In conclusion, our findings demonstrate that confined water in reverse micelles possesses an ultra-thin shell of interfacial water. We reveal the structural attributes and diffusive dynamics of water enclosed by lipid layers in multilamellar structures. Furthermore, our investigation into aggregation rates and mechanisms of insulin and a-synuclein underscores notable differences between H₂O and D₂O environments, i.e., nuclear quantum effects. I anticipate that these insights will deepen our understanding of the vital interplay between water and cellular processes at the molecular level.

Prof. Igor Schapiro

The Hebrew University of Jerusalem, Israel

Title: Shedding light on isomerization in phytochrome: Insights from computational investigations

Abstract:

Phytochromes are photoreceptor proteins that carry a linear tetrapyrrole chromophore. The chromophore absorbs light and undergoes photoisomerization which is the first step in the photocycle of these proteins [1]. We have employed computational methods such as hybrid quantum mechanics/molecular mechanics (QM/MM) to investigate the photoisomerization of the phycocyanobilin (PCB) chromophore in the protein environment of different phytochromes. The work was done in collaboration with several groups in the CRC 1078.

The changes in the geometry of the chromophore during the isomerization process were tracked using geometry optimizations along the S1 excited state by twisting the dihedral angle between rings C and D as the reaction coordinate. We focus attention on how the environment which surrounds the PCB may impact the photoisomerization process by tracking the movement of the amino acid residues as well as the hydrogen bonding interactions involving the PCB along the rotation around the dihedral in the S1 state. The photoisomerization process of the phytochrome is compared to that of a prototypical cyanobacteriochrome (CBCR) with the main target being to determine the origin of difference in the isomerization yield of the prototypical phytochrome and CBCR [2].

References

[1] Rockwell, N. C.; Lagarias, J. C. A Brief History of Phytochromes. Chemphyschem 2010, 11 (6), 1172-1180. DOI: 10.1002/cphc.200900894.
[2] Rao, A. G.; Schapiro, I. Photoisomerization of phytochrome chromophore models: an XMS-CASPT2 study. Physical Chemistry Chemical Physics 2022, 24 (48), 29393-29405, 10.1039/D2CP04249E. DOI: 10.1039/D2CP04249E