Cryo-EM Structures and Regulation of Arabinofuranosyltransferase AftD from Mycobacteria

Mol Cell. 2020 May 21;78(4):683-699.e11. doi: 10.1016/j.molcel.2020.04.014. Epub 2020 May 7.


Mycobacterium tuberculosis causes tuberculosis, a disease that kills over 1 million people each year. Its cell envelope is a common antibiotic target and has a unique structure due, in part, to two lipidated polysaccharides-arabinogalactan and lipoarabinomannan. Arabinofuranosyltransferase D (AftD) is an essential enzyme involved in assembling these glycolipids. We present the 2.9-Å resolution structure of M. abscessus AftD, determined by single-particle cryo-electron microscopy. AftD has a conserved GT-C glycosyltransferase fold and three carbohydrate-binding modules. Glycan array analysis shows that AftD binds complex arabinose glycans. Additionally, AftD is non-covalently complexed with an acyl carrier protein (ACP). 3.4- and 3.5-Å structures of a mutant with impaired ACP binding reveal a conformational change, suggesting that ACP may regulate AftD function. Mutagenesis experiments using a conditional knockout constructed in M. smegmatis confirm the essentiality of the putative active site and the ACP binding for AftD function.

Keywords: Mycobacterium tuberculosis; acyl carrier protein; arabinofuranose; glycosyltransferase; lipoarabinomannan; lipomannan; membrane protein; nanodisc; single-particle cryo-electron microscopy.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Acyl Carrier Protein / genetics
  • Acyl Carrier Protein / metabolism*
  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Catalytic Domain
  • Cell Membrane / metabolism*
  • Cell Wall / metabolism
  • Cryoelectron Microscopy / methods*
  • Galactans / metabolism
  • Glycosyltransferases / genetics
  • Glycosyltransferases / metabolism*
  • Lipopolysaccharides / metabolism
  • Mutation
  • Mycobacterium smegmatis / enzymology*
  • Mycobacterium smegmatis / genetics
  • Mycobacterium smegmatis / growth & development
  • Phylogeny
  • Protein Conformation
  • Substrate Specificity


  • Acyl Carrier Protein
  • Bacterial Proteins
  • Galactans
  • Lipopolysaccharides
  • lipoarabinomannan
  • Glycosyltransferases
  • arabinogalactan