Lipid Dependence of the Channel Properties of a Colicin E1-Lipid Toroidal Pore

Abstract

Colicin E1 belongs to a group of bacteriocins whose cytotoxicity toward Escherichia coli is exerted through formation of ion channels that depolarize the cytoplasmic membrane. The lipid dependence of colicin single-channel conductance demonstrated intimate involvement of lipid in the structure of this channel. The colicin formed "small" conductance 60-picosiemens (pS) channels, with properties similar to those previously characterized, in 1,2-dieicosenoyl-snglycero-3-phosphocholine (C20) or thinner membranes, whereas it formed a novel "large" conductance 600-pS state in thicker 1,2-dierucoyl-sn-glycero-3-phosphocholine (C22) bilayers. Both channel states were anion-selective and voltage-gated and displayed a requirement for acidic pH. Lipids having negative spontaneous curvature inhibited the formation of both channels but increased the ratio of open 600 pS to 60 pS conductance states. Different diameters of small and large channels, 12 and 16 Å , were determined from the dependence of single-channel conductance on the size of nonelectrolyte solute probes. Colicin-induced lipid "flip-flop" and the decrease in anion selectivity of the channel in the presence of negatively charged lipids implied a significant contribution of lipid to the structure of the channel, most readily described as toroidal organization of lipid and protein to form the channel pore.The lipid environment of membrane proteins that defines the local distribution of polarity, dielectric constant, and steric geometry has a central role in the determination of protein structure and function. For ion channels, lipids impose the following constraints: (i) structure-function is sensitive to the matching of hydrophobic thickness of the protein and lipid bilayer (1-10); (ii) opening of channels (e.g. mechano-sensitive, can be dependent on bilayer tension) (11), which manifests itself in a dependence on acyl chain length (12); (iii) spontaneous curvature (SC) 2 of lipids linked to the lateral pressure of the bilayer can modulate ion channel activity (13), as demonstrated for the KcsA channel (14) and mechano-sensitive MscL channels (12, 15); and (iv) many channel proteins require anionic lipids for function (16 -19).Channel-forming proteins can require specific lipids, presumably because of a combination of charge and curvature parameters, to form active channels (e.g. anionic lipid bound between the transmembrane ␣-helices and necessary for gating of the KcsA channel (20, 21)). The lantibiotic nisin provides a well defined example of lipid participation in peptide pore formation, in which the peptidoglycan precursor lipid II is an intrinsic component of the pore formed by this antimicrobial peptide (22). The proposed structure of this pore contains 5-8 nisin molecules and an identical number of lipid II molecules (23). Participation of lipid in the formation of a channel wall was hypothesized for cholesteroldependent cytolysins (24,25).Colicins are plasmid-encoded bacteriocins that are cytotoxic to Escherichia coli and related strains. Their modes of ...

Colicin Biology

“…Such a mechanism has been suggested for certain peptides that form multimeric pores (405,450,451), but it is not yet clear how it could be applied to colicin. Recently, however, evidence in support of this proposal has been reported (605,606).…”

Perforin oligomers form arcs in cellular membranes: a locus for intracellular delivery of granzymes

“…Phenotypically, this translates to the anticipated blockade of cylindrical pore formation in simple planar bilayers and complex plasma membrane where functionality of an arc is defined respectively by measurable conductance and PS flip-flop. 20 Notably, during the AFM experiments, pf-80 mAb increases the total number of structures. This outcome is consistent with the formation of twenty-mer cylindrical pores in the absence of pf-80 but of arcs varying in size between 6 to 10 mer in the presence of the Figure 1.…”

“…19,20 In contrast to a cylindrical pore which is lined exclusively by protein that barricades phospholipid movement across the bilayer, 21,22 a toroidal pore (alternately termed proteolipid, lipidic or 'leaky slit' pore) consists of inserted peptides (or proteins) and lipid together forming a water channel. During the formation of such structures, transbilayer curvature is promoted leading to merger of the inner and outer leaflets.…”

Tim17p Regulates the Twin Pore Structure and Voltage Gating of the Mitochondrial Protein Import Complex TIM23

“…These marked differences in channel behavior are likely due to reconstitution and/or the influence of other components, almost certainly Tim17p and possibly Tim50p whose role in closing TIM23 was recently reported (50). Differences in membrane curvature and/or fluidity may also be contributing factors as reported in other systems (51,52). For example, the conductance of colicin E1 channels changes from 60 to 600 pS depending on the lipid environment (51).…”

“…Differences in membrane curvature and/or fluidity may also be contributing factors as reported in other systems (51,52). For example, the conductance of colicin E1 channels changes from 60 to 600 pS depending on the lipid environment (51).…”