Structure of colicin I receptor bound to the R-domain of colicin Ia: implications for protein import

Abstract

Colicin Ia is a 69 kDa protein that kills susceptible Escherichia coli cells by binding to a specific receptor in the outer membrane, colicin I receptor (70 kDa), and subsequently translocating its channel forming domain across the periplasmic space, where it inserts into the inner membrane and forms a voltage-dependent ion channel. We determined crystal structures of colicin I receptor alone and in complex with the receptor binding domain of colicin Ia. The receptor undergoes large and unusual conformational changes upon colicin binding, opening at the cell surface and positioning the receptor binding domain of colicin Ia directly above it. We modelled the interaction with full-length colicin Ia to show that the channel forming domain is initially positioned 150 Å above the cell surface. Functional data using full-length colicin Ia show that colicin I receptor is necessary for cell surface binding, and suggest that the receptor participates in translocation of colicin Ia across the outer membrane.

Novel Colicin F Y of Yersinia frederiksenii Inhibits Pathogenic Yersinia Strains via YiuR-Mediated Reception, TonB Import, and Cell Membrane Pore Formation

“…Although YiuABC proteins were shown to be involved in the iron acquisition system in Y. pestis, YiuR was not required for iron uptake (35); as a result, the function of the predicted outer membrane receptor YiuR protein remains unknown. YiuR displayed 37% identity with the Cir protein of E. coli involved in iron acquisition and in colicin and microcin uptake (9,11,33,37,50). Interestingly, introduction of the yiuR gene into E. coli strain TOP10F= did not restore susceptibility to colicin F Y .…”

“…Residues interacting with colicin F Y are likely to be found on externally exposed loops 1 to 11 of the YiuR receptor (Table 5). For comparison, most of the sites of interaction between the receptor domain of colicin Ia and the Cir receptor (homologous to YiuR) were identified in Cir loops L7 and L8 (9). Interestingly, these loops in the YiuR receptor are the longest and most divergent between Y. kristensenii and Y. pseudotuberculosis (Table 5) and may therefore specify interaction with colicin F Y .…”

The Colicin E1 TolC Box: Identification of a Domain Required for Colicin E1 Cytotoxicity and TolC Binding

“…For colicins E3 and E9, segments of their T domains were shown to be bound inside the pore of OmpF (14)(15)(16), and their T domains have also been shown to occlude OmpF channels in planar lipid bilayer membranes (16,17). For colicin Ia, a pore-forming colicin, a second copy of its Cir receptor serves as its translocator (10,18). The colicin's R domain binds to Cir with high affinity, allowing for a more efficient search, while anchored at the cell surface, by its T domain for another nearby copy of Cir, through which it transits into the periplasm by an as-yet poorly understood mechanism that must involve some movement of the plug domain of Cir.…”

“…These receptors are all 22-stranded ␤-barrels with an N-terminal periplasmfacing plug that fills the barrel (6,7). Structures have been solved for a number of these receptors with bound colicin R domains: colicins E3 and E2 bound to their BtuB receptor (8,9), and colicin Ia bound to Cir (10). Once the colicin is bound at the cell surface, however, it must still cross the membrane on which it is bound.…”

Reconstitution of bacterial outer membrane TonB-dependent transporters in planar lipid bilayer membranes

“…1). The crystal structure of a number of these ␤-barrels has been determined (2)(3)(4)(5)(6)(7)(8), and in addition to being 22-stranded, they share the unusual feature that their N-terminal end inserts from the periplasmic side into the ␤-barrel and plugs the lumen (Fig. 1).…”