Milan Dimitrovski

Milan

Dimitrovski

MMRES student at ICIQ and CRG
Class 2019-2020

Salt effects on the structure of de novo proteins used as bio-inspired chromophore holders for light harvesting

Summary

The world consumption of the limited fossil fuels combined with its negative environmental effects has prompted research towards clean and efficient renewable energy sources. Among wind and hydro energy, solar has been the leading source and the invention of photovoltaic (PV) cells and solar panels has facilitated the process. However, with the average solar panel operating around 20% light conversion efficiency, perhaps the answer towards the future of renewable energy sources lies within the photosynthetic process. Over the course of millions of years, plants, algae and some bacteria have evolved to fine tune natural systems which enable light harvesting and charge transfer of near 100% efficiency. The main components which drive this process are pigment-protein complexes (PPC). Here, we shown successful incorporation of pigment analogues (chromophores) into specially designed de novo proteins. Three different protein designs were tested, two of which form a 4-alpha helix structures (potentially forming H or J chromophore aggregates) and one which forms a 5-alpha-helix bundle (aiming to form J aggregates). Titration experiments in which molar excess of chromophores are added and were followed by UV-Vis Absorption spectroscopy and Circular Dichroism (CD) in two different salt concentrations: low (150mM KCl) and high (1M KCl). Absorption spectroscopy allowed us to determine that some protein designs retain at least two chromophores within the structure and that increased salt concentration enhances the chromophore retention. CD spectra of purified complexes confirms presence of excitonic interactions in one protein design only in high salt condition. Hereby, we show the improvements made towards a greater chromophore retention in synthetic PPCs via increasing the buffer ionic strength, changing histidine linking locations and addition of an extra alpha helix.

Major project supervisor

Elisabet Romero
ICIQ

Minor project supervisor

Carlo Carolis
CRG