Journal Article

Structure of an endogenous mycobacterial MCE lipid transporter

Fruhauf, Alice, Ueberheide, Beatrix, Bhabha, Gira, Ponce, Jackeline, Ekiert, Damian C., Chen, James, Fan, Catherine

2023

Overview

To replicate inside macrophages and cause tuberculosis, Mycobacterium tuberculosis must scavenge a variety of nutrients from the host 1 , 2 . The mammalian cell entry (MCE) proteins are important virulence factors in M. tuberculosis 1 , 3 , where they are encoded by large gene clusters and have been implicated in the transport of fatty acids 4 – 7 and cholesterol 1 , 4 , 8 across the impermeable mycobacterial cell envelope. Very little is known about how cargos are transported across this barrier, and it remains unclear how the approximately ten proteins encoded by a mycobacterial mce gene cluster assemble to transport cargo across the cell envelope. Here we report the cryo-electron microscopy (cryo-EM) structure of the endogenous Mce1 lipid-import machine of Mycobacterium smegmatis —a non-pathogenic relative of M. tuberculosis . The structure reveals how the proteins of the Mce1 system assemble to form an elongated ABC transporter complex that is long enough to span the cell envelope. The Mce1 complex is dominated by a curved, needle-like domain that appears to be unrelated to previously described protein structures, and creates a protected hydrophobic pathway for lipid transport across the periplasm. Our structural data revealed the presence of a subunit of the Mce1 complex, which we identified using a combination of cryo-EM and AlphaFold2, and name LucB. Our data lead to a structural model for Mce1-mediated lipid import across the mycobacterial cell envelope. Proteins of the Mycobacterium smegmatis Mce1 system assemble to form an elongated ABC transporter complex that is long enough to span the impermeable mycobacterial cell envelope.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 101/28 / 631/326/41/2536 / 631/326/421 / 631/45/612/1237 / 631/535/1258/1259 / 631/57/2271 / 82/16 / 82/58 / 82/80 / 82/83 / ABC transporter / ABC transporters / Animals / ATP-Binding Cassette Transporters - chemistry / ATP-Binding Cassette Transporters - metabolism / ATP-Binding Cassette Transporters - ultrastructure / Bacterial Proteins - chemistry / Bacterial Proteins - metabolism / Bacterial Proteins - ultrastructure / Cholesterol / Cryoelectron Microscopy / Electron microscopy / Fatty acids / Gene clusters / Genes / Genomes / Humanities and Social Sciences / Hydrophobic and Hydrophilic Interactions / Hydrophobicity / Imports / Lipids / Macrophages / Membrane Transport Proteins - chemistry / Membrane Transport Proteins - metabolism / Membrane Transport Proteins - ultrastructure / multidisciplinary / Multiprotein Complexes - chemistry / Multiprotein Complexes - metabolism / Multiprotein Complexes - ultrastructure / Mycobacterium tuberculosis - chemistry / Mycobacterium tuberculosis - metabolism / Mycobacterium tuberculosis - ultrastructure / Nutrients / Periplasm / Periplasm - metabolism / Protein Domains / Proteins / Science / Science (multidisciplinary) / Structural models / Tuberculosis / Tuberculosis - microbiology / Virulence / Virulence factors / Virulence Factors - chemistry / Virulence Factors - metabolism / Virus Internalization