Protein evolution is driven by random drift, selective pressure and epistasis. Here the degree of conformational epistasis in the evolution of a protein-protein interface, the Gyrase-CcdB complex, is analysed. The study is based in the ancestor reconstruction of the C-terminal a-helix of the CcdB proteins encoded on the chromosomes and plasmids of proteobacteria. As this C-terminus is responsible for interacting with Gyrase and ultimately producing bacterial cell death, in vivo toxicity assays were used taking advantage of this CcdB poison ability. Two evolutionary pathways of the C-terminal segment of CcdB are proposed with each intermediates being functional, each of which leads to the highly studied V. fischeri CcdB and F-plasmid CcdB. A case of strong conformational epistasis can be observed in the amino acids 91 and 95 which must be coupled. Also, the importance of the context dependence of the functionality of the Gyrase binding site of CcdB is proven. Finally, our test system enables us to hypothesize that chromosomal CcdBs have a lower activity than plasmid encoded CcdBs.
Ancestor reconstruction of the bacterial Gyrase poison CcdB
Bermejo Diez, I. ((PhD) Student), Loris, R. (Promotor), De Greve, H. (Promotor). 29 jun 2018
Scriptie/Masterproef: Master's Thesis