Biochemical characterization of the first step in sulfonolipid biosynthesis in Alistipes finegoldii

Christopher D. Radka, Darcie J. Miller, Matthew W. Frank, Charles O. Rock

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


Sulfonolipids are unusual lipids found in the outer membranes of Gram-negative bacteria in the phylum Bacteroidetes. Sulfonolipid and its deacylated derivative, capnine, are sulfur analogs of ceramide-1-phosphate and sphingosine-1-phosphate, respectively; thus, sulfonolipid biosynthesis is postulated to be similar to the sphingolipid biosynthetic pathway. Here, we identify the first enzyme in sulfonolipid synthesis in Alistipes finegoldii as the product of the alfi_1224 gene, cysteate acyl-acyl carrier protein (ACP) transferase (SulA). We show SulA catalyzes the condensation of acyl-ACP and cysteate (3-sulfo-alanine) to form 3-ketocapnine. Acyl-CoA is a poor substrate. We show SulA has a bound pyridoxal phosphate (PLP) cofactor that undergoes a spectral redshift in the presence of cysteate, consistent with the transition of the lysine–aldimine complex to a substrate–aldimine complex. Furthermore, the SulA crystal structure shows the same prototypical fold found in bacterial serine palmitoyltransferases (Spts), enveloping the PLP cofactor bound to Lys251. We observed the SulA and Spt active sites are identical except for Lys281 in SulA, which is an alanine in Spt. Additionally, SulA(K281A) is catalytically inactive but binds cysteate and forms the external aldimine normally, highlighting the structural role of the Lys281 side chain in walling off the active site from bulk solvent. Finally, the electropositive groove on the protein surface adjacent to the active site entrance provides a landing pad for the electronegative acyl-ACP surface. Taken together, these data identify the substrates, products, and mechanism of SulA, the PLP-dependent condensing enzyme that catalyzes the first step in sulfonolipid synthesis in a gut commensal bacterium.

Original languageEnglish
Article number102195
JournalJournal of Biological Chemistry
Issue number8
StatePublished - Aug 2022

Bibliographical note

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© 2022 The Authors


  • 3-ketocapnine
  • Alistipes finegoldii
  • Bacteroidetes
  • condensing enzyme
  • crystal structure
  • fatty acid
  • gut microbiome
  • sulfonolipid biosynthesis

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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