Investigation of the enzymes required for the biosynthesis of an unusual formylated sugar in the emerging human pathogen Helicobacter canadensis

Protein Sci. 2021 Oct;30(10):2144-2160. doi: 10.1002/pro.4169. Epub 2021 Aug 31.


It is now well established that the Gram-negative bacterium, Helicobacter pylori, causes gastritis in humans. In recent years, it has become apparent that the so-called non-pylori Helicobacters, normally infecting pigs, cats, and dogs, may also be involved in human pathology via zoonotic transmission. Indeed, more than 30 species of non-pylori Helicobacters have been identified thus far. One such organism is Helicobacter canadensis, an emerging pathogen whose genome sequence was published in 2009. Given our long-standing interest in the biosynthesis of N-formylated sugars found in the O-antigens of some Gram-negative bacteria, we were curious as to whether H. canadensis produces such unusual carbohydrates. Here, we demonstrate using both biochemical and structural techniques that the proteins encoded by the HCAN_0198, HCAN_0204, and HCAN_0200 genes in H. canadensis, correspond to a 3,4-ketoisomerase, a pyridoxal 5'-phosphate aminotransferase, and an N-formyltransferase, respectively. For this investigation, five high-resolution X-ray structures were determined and the kinetic parameters for the isomerase and the N-formyltransferase were measured. Based on these data, we suggest that the unusual sugar, 3-formamido-3,6-dideoxy-d-glucose, will most likely be found in the O-antigen of H. canadensis. Whether N-formylated sugars found in the O-antigen contribute to virulence is presently unclear, but it is intriguing that they have been observed in such pathogens as Francisella tularensis, Mycobacterium tuberculosis, and Brucella melitensis.

Keywords: N-formyltransferase; X-ray crystallography; aminotransferase; carbohydrate; enzyme kinetics; folate; ketoisomerase; pyridoxal 5′-phosphate; structure-function; tertiary structure.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Bacterial Proteins* / chemistry
  • Bacterial Proteins* / genetics
  • Bacterial Proteins* / metabolism
  • Carbohydrate Metabolism*
  • Carbohydrates* / biosynthesis
  • Carbohydrates* / chemistry
  • Carbohydrates* / genetics
  • Crystallography, X-Ray
  • Helicobacter pylori / enzymology
  • Helicobacter pylori / genetics
  • Helicobacter* / enzymology
  • Helicobacter* / genetics


  • Bacterial Proteins
  • Carbohydrates

Supplementary concepts

  • Helicobacter canadensis