Bacteria produce an astonishingly diverse array of carbohydrate-based macromolecules that serve important physiological roles. The lipopolysaccharide or LPS, for example, is a complex glycoconjugate attached to the outer membranes of Gram-negative bacteria. It is often composed of unusual dideoxysugars that may be important for virulence.
Recent research has demonstrated that some pathogenic Gram-negative bacteria contain quite remarkable N-formylated dideoxysugars. These organisms include, for example, Campylobacter jejuni, which is one of the most common causes of gastroenteritis worldwide and a risk factor for the development of Guillain-Barré syndrome, and Francisella tularensis, the causative agent of rabbit fever.
The N-formylated sugars found in these organisms are synthesized by complex pathways that involve N-formyltransferases. From our research the three-dimensional structures of five of these enzymes from various organisms have been defined. Very recently we demonstrated that one of these enzymes, in addition to containing the classical N-formyltransferase fold, also has an ankyrin repeat domain. Whereas the ankyrin repeat is a common eukaryotic motif involved in protein-protein interactions, reports of its presence in prokaryotic enzymes have been limited. Unexpectedly, this ankyrin repeat was shown to house a second binding pocket for the enzyme’s substrate. Our subsequent kinetic analyses demonstrated that this additional binding pocket is involved in allosteric regulation.
This is the first example of an ankyrin repeat being involved in small molecule binding and allosteric control. Our work thus paves the way for new investigations focusing on the use of ankyrin repeat in small molecule binding and allosteric regulation.
Papers describing Holden lab research on N-formyltransferases:
Three-dimensional structure of a sugar N-formyltransferase from Francisella tularensis. Zimmer, A. L., Thoden, J. B., and Holden, H. M. (2014) Protein Science, 23, 273-283.
A new role for the ankyrin repeat revealed by the study of the N-formyltransferase from Providencia alcalifaciens.Woodford, C. R., Thoden, J. B., and Holden, H. M. (2015) Biochemistry, 54, 631-638.
Molecular structure of an N-formyltransferase from Providencia alcalifaciens O30. Genthe, N. A., Thoden, J. B., Benning, M. M., and Holden, H. M. (2015) Protein Science, accepted for publication.