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Figure 1
(a) Part of the mce1 and mce4 operons of Mtb encoding permeases (YrbEA–B), SBPs (MceA–F) and Mam proteins. (b) Lipid-transporter complexes from E. coli [EcMlaFEDB (PDB entry 6zy2), EcPqiB (PDB entry 5uvn) and EcLetB (PDB entry 6v0c)] for which structural information has been reported (Ekiert et al., 2017BB10; Isom et al., 2020BB16; Tang et al., 2021BB46). Lipid transport by the EcMlaFEDB complex depends on a ferry-based lipid-transport mechanism, whereas the EcPqiB and EcLetB complexes facilitate a tunnel-based transport mechanism (Ekiert et al., 2017BB10; Kamischke et al., 2019BB19; Coudray et al., 2020BB8; Isom et al., 2020BB16; Liu et al., 2020BB24; Mann et al., 2020BB25). OM is the outer membrane of Mtb, PG is peptidoglycan and IM is the inner membrane. In each of these transporters the MCE domains are assembled into hexameric rings that stabilize the assembled homohexameric complexes.

IUCrJ
Volume 8| Part 5| September 2021| Pages 757-774
ISSN: 2052-2525
https://doi.org/10.1107/S2052252521006199