WciG O -Acetyltransferase Functionality Differentiates Pneumococcal Serotypes 35C and 42

Abstract

Streptococcus pneumoniae expresses capsular polysaccharides (CPSs) to protect itself from opsonophagocytic killing. The genes responsible for capsules synthesized by the Wzy-dependent mechanism, which accounts for 96 of the 98 known pneumococcal capsule types, are in a chromosomal region known as the cps locus. The nucleotide sequence in this region has been determined for all serotypes. In contrast, not all CPS structures have been defined. The structure of the serotype 35C polysaccharide was recently reported, but the presence of O-acetyltransferase genes in the serotype 35C cps locus suggested that it could be incomplete, as the reported structure contains no O-acetylation. In addition, the genetic distinction of serotype 35C from the closely related serotype 42 was unclear, as their reported cps loci are nearly identical. To clarify these discrepancies, we obtained serotype 35C and 42 clinical and reference isolates and studied their serological and genetic properties, as well as the structures of CPSs purified from reference isolates. We demonstrated that the Oacetyltransferase WciG was functional in serotype 35C but nonfunctional in serotype 42 due to a deletion in wciG. Serotype 35C was O-acetylated at the 5-and 6-positions of 3-␤-galactofuranose, as well as the 2-position of 6-␤-galactofuranose. However, serotype 42 has only O-acetylation at 3-␤-galactofuranose, an observation consistent with its loss of WciG functionality, which is associated with O-acetylation at the 2-position and subsequent reaction with typing antiserum 35a. These findings provide a comprehensive view of the genetic, biochemical structural, and serological bases of serotypes 35C and 42.

Discovery of a Streptococcus pneumoniae serotype 33F capsular polysaccharide locus that lacks wcjE and contains a wcyO pseudogene

“…Whether the mutation of wcyO is due to selective pressure to inactivate a disadvantageous gene or due to a lack of selective advantage to maintain it remains to be investigated. Previously, mutations have been identified in other pneumococcal capsule acetyltransferase genes including wciG [ 24 ] and wcjE [ 22 , 25 , 26 ]. Serotype 11E, which lacks WcjE-mediated acetylation can evade opsonophagocytosis more efficiently compared to 11A (which possess WcjE-mediated acetylation) [ 25 ].…”

Bacterial polysaccharides as major surface antigens: interest in O-acetyl substitutions

“…pneumoniae serotype pairing through functional/non-functional acetyltransferases 20 has become increasingly relevant. It was demonstrated to be occasionally associated to mistyping, 98 especially since some isolates may express reduced amount of Oacetylation, a per se labile and possibly variable CPS substitution. In this regard, the S. pneumoniae 42 mistyping as S. pneumoniae 35C is an exquisite example.…”

“…12C). 98 The updated repeating unit for S. pneumoniae 35C CPS has the WcjE-controlled O-acetylation at OH-5 and OH-6 of the →3)-D-Galf residue in common with the repeating units from the CPS 30 of serotypes 35A (Fig 12A) and 42 (Fig. 12C).…”

Structural, Biosynthetic, and Serological Cross-Reactive Elucidation of Capsular Polysaccharides from Streptococcus pneumoniae Serogroup 16

“…Thus, the only unassigned GT (WcxT) was assigned, by process of elimination, as being responsible for catalyzing the linkage of ␣-L-Rhap-(1-2)-␣-L-Rhap. WciG, a putative acetyltransferase, catalyzed 2-O-acetylation at ␤-D-Galf (26)(27)(28)(29). WcxR is a putative LicD family phosphotransferase that was assigned to catalyze phosphorylation at the 6 position of ␣-D-Galp.…”