Colicins are toxic molecules secreted to kill other bacteria in times of stress. Colicin Ia kills susceptible E.coli cells by binding to the colicin I receptor leading to the formation of a voltage-dependant ion channel. The protein can be divided into three domains, a translocation domain, a receptor binding domain and a channel forming domain [1].

1: Structure of colicin I receptor bound to the R-domain of colicin Ia: implications for protein import. Buchanan SK, Lukacik P, Grizot S, Ghirlando R, Ali MM, Barnard TJ, Jakes KS, Kienker PK, Esser L; EMBO J. 2007;26:2594-2604. PMID:17464289