Berlin 2024 – scientific programme

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BP: Fachverband Biologische Physik

BP 6: Bacterial Biophysics I

BP 6.7: Talk

Monday, March 18, 2024, 17:00–17:15, H 1028

Ultrasensitive dependence of fitness costs on membrane protein overexpression — •Janina Müller, Andreas Angermayr, Gerrit Ansmann, and Tobias Bollenbach — Institute for Biological Physics, University of Cologne

Perturbing expression levels of genes is a key technique for studying their function. In E. coli, strong overexpression of gratuitous proteins leads to fitness costs that are partially predictable from bacterial growth laws and sector models of proteome allocation. Here, we systematically quantified the precise dependence of fitness costs on the level of overexpression using a genome-wide library. Our results confirm that the fitness cost for membrane proteins is extremely high compared to cytosolic proteins, and reveal that this cost is ultrasensitive to the expression level. To elucidate the mechanisms underlying this ultrasensitive response to membrane protein overexpression, we characterized the role of membrane translocation by examining the fitness costs of mutants of a model membrane protein with different translocation requirements, resulting in a reduction in translocation success. Single-cell experiments to detect membrane localization using protein-GFP fusions further demonstrated that overexpression of membrane proteins leads to displacement of other membrane proteins. This displacement closely coincides with the abrupt collapse of the growth rate. A minimal physical model can explain these observations and suggests that the abrupt growth collapse is caused by zero-order ultrasensitivity in the translocation pathway.

Keywords: protein overexpression; growth laws