Over the last decade, there has been a growing body of experimental work showing that proteins devoid of aromatic and conjugated groups can absorb light in the near-UV beyond 300 nm and emit visible light. Understanding the origins of this phenomena offers the possibility of designing non-invasive spectroscopic probes for local interactions in biological systems. It was recently found that the synthetic protein Alpha-3C exhibits UV–vis absorption between 250–800 nm [1], and emission between 310–550 nm upon excitation at 295 nm [2]. Remarkably, this behavior occurs in the absence of aromatic or conjugated groups, which are typically responsible for near-UV absorption and emission.
In this talk, I will discuss how we investigated the structural origins of the this unconventional optical response. Specifically, an unsupervised machine-learning approach was employed to automatically identify statistically significant structural motifs. These motifs were then subjected to QM/MM simulations of the full protein in explicit solvent, employing density-functional tight binding (DFTB) for the ground state and its time-dependent extension (TD-DFTB) for excited states. This integrated workflow enables the efficient identification of key structural motifs and their direct connection to the observed absorption and emission features. We found that hydrogen bonding between carboxylate and guanidinium groups was crucial for near-UV absorption [3], while the stability of the helical structure played a key role in the observed emission.

[1] S. Prasad, et al., Chem. Sci. (2017)
[2] A. Kumar, et al., Biophysical J. (2022)
[3] G. Neza Hozana, et al., J. Phys. Chem. B (2025)

Biography:

Dr. Germaine Neza Hozana is a physicist by training, interested in understanding physical principles that govern biomolecular systems. She obtained a BSc. in Physics from the University of Rwanda's College of Science and Technology, then pursued a master's degree in Mathematical Sciences at the African Institute for Mathematical Sciences (AIMS) Rwanda.

Dr. Neza Hozana later moved to Italy, specifically to the Abdus Salam International Centre for Theoretical Physics (ICTP) to undertake a postgraduate diploma training in Condensed Matter Physics, followed by a joint PhD Fellowship with the ICTP and University of Trieste. Her doctoral research, recently defended,  used computational and machine learning methods to study unconventional optical properties of nonaromatic proteins. She is expecting graduation this July.