A couple of caveats should be mentioned regarding the use of APols to deliver MPs to preformed
membranes. First, the carrier APols will themselves become inserted into the target membrane
(cf. Pocanschi et al. 2006b; Popot et al. 2011), even though, very likely, they will dissociate from
the protein and migrate independently from it (cf. the separation of BR from A8-35 upon transfer of the
complexes to a lipidic mesophase; see below). They may cause perturbations that have to be paid
attention to. Indeed, the conductance of the pores formed by OmpA and FomA delivered to a black
film was abnormally low until A8-35 was also added to the trans compartment, indicating that the
asymmetry created by APol binding to one side only of the film perturbed the function of the channel
(Fig. 5.41; Pocanschi et al. 2006a, b). Second, not all MPs can be expected to survive such a drastic
Fig. 5.41 Delivery of two membrane proteins from A8-35 to a black lipid film. Single-channel recordings
of refolded OmpA (from E. coli) and FomA (from Fusobacterium nucleatum) integrated into black lipid
films. (A) OmpA. (a) Large-conductance (1) and small-conductance (2) states observed when A8-35refolded OmpA was added to the cis side of a diphytanoylphosphatidylcholine film. The conductance of
the small-conductance state increased when A8-35 was added to the trans side (3). No event was observed
in the presence of A8-35 alone, whether added in trans (not shown), in cis (4), or on both sides of the film
(not shown), or in that of unfolded OmpA (5). (b, c) Distribution of small-conductance states observed
after addition of A8-35/OmpA complexes to the cis side in the absence (b) or presence (c) of A8-35 on the
trans side. (B) FomA. (a) Channels formed by A8-35-refolded FomA added to the cis side with A8-35
present (1) or absent (2) in the trans compartment and control experiments with LDAO-refolded FomA
(3), with A8-35 only (on the cis side) (4), and with denatured FomA (5). (b, c) Distribution of conductance
states observed after addition of FomA/A8-35 complexes to the cis side without (b) and with (c) A8-35
added to the trans side (Reprinted with permission from Pocanschi et al. 2006a, b, # 2006 American
Chemical Society).
5.7 Transferring Membrane Proteins from Amphipols to Other Environments
309
membranes. First, the carrier APols will themselves become inserted into the target membrane
(cf. Pocanschi et al. 2006b; Popot et al. 2011), even though, very likely, they will dissociate from
the protein and migrate independently from it (cf. the separation of BR from A8-35 upon transfer of the
complexes to a lipidic mesophase; see below). They may cause perturbations that have to be paid
attention to. Indeed, the conductance of the pores formed by OmpA and FomA delivered to a black
film was abnormally low until A8-35 was also added to the trans compartment, indicating that the
asymmetry created by APol binding to one side only of the film perturbed the function of the channel
(Fig. 5.41; Pocanschi et al. 2006a, b). Second, not all MPs can be expected to survive such a drastic
Fig. 5.41 Delivery of two membrane proteins from A8-35 to a black lipid film. Single-channel recordings
of refolded OmpA (from E. coli) and FomA (from Fusobacterium nucleatum) integrated into black lipid
films. (A) OmpA. (a) Large-conductance (1) and small-conductance (2) states observed when A8-35refolded OmpA was added to the cis side of a diphytanoylphosphatidylcholine film. The conductance of
the small-conductance state increased when A8-35 was added to the trans side (3). No event was observed
in the presence of A8-35 alone, whether added in trans (not shown), in cis (4), or on both sides of the film
(not shown), or in that of unfolded OmpA (5). (b, c) Distribution of small-conductance states observed
after addition of A8-35/OmpA complexes to the cis side in the absence (b) or presence (c) of A8-35 on the
trans side. (B) FomA. (a) Channels formed by A8-35-refolded FomA added to the cis side with A8-35
present (1) or absent (2) in the trans compartment and control experiments with LDAO-refolded FomA
(3), with A8-35 only (on the cis side) (4), and with denatured FomA (5). (b, c) Distribution of conductance
states observed after addition of FomA/A8-35 complexes to the cis side without (b) and with (c) A8-35
added to the trans side (Reprinted with permission from Pocanschi et al. 2006a, b, # 2006 American
Chemical Society).
5.7 Transferring Membrane Proteins from Amphipols to Other Environments
309