Abstract
ABC transporters facilitate the movement of diverse molecules across cellular membranes, but how their activity is regulated post-translationally is not well understood. Here we report the crystal structure of MlaFB from E. coli, the cytoplasmic portion of the larger MlaFEDB ABC transporter complex, which drives phospholipid trafficking across the bacterial envelope to maintain outer membrane integrity. MlaB, a STAS domain protein, binds the ABC nucleotide binding domain, MlaF, and is required for its stability. Our structure also implicates a unique C-terminal tail of MlaF in self-dimerization. Both the C-terminal tail of MlaF and the interaction with MlaB are required for the proper assembly of the MlaFEDB complex and its function in cells. This work leads to a new model for how an important bacterial lipid transporter may be regulated by small proteins, and raises the possibility that similar regulatory mechanisms may exist more broadly across the ABC transporter family.
Highlights
ATP Binding Cassette (ABC) transporters catalyze the import or export of a wide range of molecules across cellular membranes, including ions[1], drugs[2], antibiotics[3], sugars[4], lipids[5,6,7,8,9], and even large proteins[10]
Overview of the MlaFB crystal structure MlaF and MlaB are both required for the proper functioning of the Mla transport system in E. coli[19,20,24]
Consistent with these previous reports, an in-frame deletion of mlaF from the E. coli chromosome compromises outer membrane integrity, leading to poor growth of the mutant relative to the wild type strain on LB agar in the presence of OM perturbing agents such as SDS and EDTA, which can be complemented by providing a wild type copy of mlaF on a plasmid (Figure 1B; Tables S1 and S2)
Summary
ABC transporters catalyze the import or export of a wide range of molecules across cellular membranes, including ions[1], drugs[2], antibiotics[3], sugars[4], lipids[5,6,7,8,9], and even large proteins[10] Named for their conserved ATP Binding Cassette (ABC) nucleotide binding domains (NBD), ABC transporters use energy from ATP hydrolysis by the NBDs to drive conformational changes in their associated transmembrane domains (TMD) in order to translocate substrates across a lipid bilayer. A small but growing number of regulatory proteins have been shown to stimulate or inhibit ABC transporter activity, such as MetNI13, ModBC14, MalFGK15,16, and CFTR17,18 These interaction-based mechanisms of transporter regulation may be quite common but underrepresented in the literature, as identification of protein-protein interactions involving membrane proteins is challenging, and frequently screens for protein-protein interactions are biased towards soluble proteins (e.g., yeast 2-hybrid). We report structures of the MlaFB complex, and present a model for how these two proteins may work together
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
