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| Title | Cryo-EM structure of the full-length WzmWzt ABC transporter required for lipid-linked O antigen transport. |
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| Journal, issue, pages | Proc Natl Acad Sci U S A, Vol. 118, Issue 1, Year 2021 |
| Publish date | Jan 5, 2021 |
 Authors | Christopher A Caffalette / Jochen Zimmer /  |
| PubMed Abstract | O antigens are important cell surface polysaccharides in gram-negative bacteria where they extend core lipopolysaccharides in the extracellular leaflet of the outer membrane. O antigen structures are ...O antigens are important cell surface polysaccharides in gram-negative bacteria where they extend core lipopolysaccharides in the extracellular leaflet of the outer membrane. O antigen structures are serotype specific and form extended cell surface barriers endowing many pathogens with survival benefits. In the ABC transporter-dependent biosynthesis pathway, O antigens are assembled on the cytosolic side of the inner membrane on a lipid anchor and reoriented to the periplasmic leaflet by the channel-forming WzmWzt ABC transporter for ligation to the core lipopolysaccharides. In many cases, this process depends on the chemical modification of the O antigen's nonreducing terminus, sensed by WzmWzt via a carbohydrate-binding domain (CBD) that extends its nucleotide-binding domain (NBD). Here, we provide the cryo-electron microscopy structure of the full-length WzmWzt transporter from bound to adenosine triphosphate (ATP) and in a lipid environment, revealing a highly asymmetric transporter organization. The CBDs dimerize and associate with only one NBD. Conserved loops at the CBD dimer interface straddle a conserved peripheral NBD helix. The CBD dimer is oriented perpendicularly to the NBDs and its putative ligand-binding sites face the transporter to likely modulate ATPase activity upon O antigen binding. Further, our structure reveals a closed WzmWzt conformation in which an aromatic belt near the periplasmic channel exit seals the transporter in a resting, ATP-bound state. The sealed transmembrane channel is asymmetric, with one open and one closed cytosolic and periplasmic portal. The structure provides important insights into O antigen recruitment to and translocation by WzmWzt and related ABC transporters. |
 External links | Proc Natl Acad Sci U S A / PubMed:33443152 / PubMed Central |
| Methods | EM (single particle) |
| Resolution | 3.6 Å |
| Structure data | EMDB-22644, PDB-7k2t: |
| Chemicals |  ChemComp-ATP:  ChemComp-MG: |
| Source |
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 Keywords | TRANSPORT PROTEIN / O antigen transporter / integral membrane protein / lipopolysaccharide LPS biosynthesis |
Aquifex aeolicus VF5 (bacteria)