A Conserved UDP-Glucose Dehydrogenase Encoded outside the hasABC Operon Contributes to Capsule Biogenesis in Group A Streptococcus

Abstract

g Group A Streptococcus (GAS) is a human-specific bacterial pathogen responsible for serious morbidity and mortality worldwide. The hyaluronic acid (HA) capsule of GAS is a major virulence factor, contributing to bloodstream survival through resistance to neutrophil and antimicrobial peptide killing and to in vivo pathogenicity. Capsule biosynthesis has been exclusively attributed to the ubiquitous hasABC hyaluronan synthase operon, which is highly conserved across GAS serotypes. Previous reports indicate that hasA, encoding hyaluronan synthase, and hasB, encoding UDP-glucose 6-dehydrogenase, are essential for capsule production in GAS. Here, we report that precise allelic exchange mutagenesis of hasB in GAS strain 5448, a representative of the globally disseminated M1T1 serotype, did not abolish HA capsule synthesis. In silico whole-genome screening identified a putative HasB paralog, designated HasB2, with 45% amino acid identity to HasB at a distant location in the GAS chromosome. In vitro enzymatic assays demonstrated that recombinant HasB2 is a functional UDP-glucose 6-dehydrogenase enzyme. Mutagenesis of hasB2 alone slightly decreased capsule abundance; however, a ⌬hasB ⌬hasB2 double mutant became completely acapsular. We conclude that HasB is not essential for M1T1 GAS capsule biogenesis due to the presence of a newly identified HasB paralog, HasB2, which most likely resulted from gene duplication. The identification of redundant UDP-glucose 6-dehydrogenases underscores the importance of HA capsule expression for M1T1 GAS pathogenicity and survival in the human host.

Induction of a quorum sensing pathway by environmental signals enhances group A streptococcal resistance to lysozyme

“…This gene was also identified by Transposon‐Site Hybridization (TraSH) following passage in blood (Le Breton et al ., ). Additionally, hasB2 ( spy49_0459 ) was found to contribute to hyaluronic acid capsule biosynthesis and compensated for hasB1 mutants (Cole et al ., ). These enzymes serve as UDP‐glucose dehydrogenases and upregulation of hasB2 by Rgg‐SHP signaling supports the prospect that glycosylation of a capsule or other substrate outside the cell is altered by pheromones.…”

Comparative genomic analysis of Myroides odoratimimus isolates

“…Both source of this enzyme can catalyze the conversion of UDP‐GlcNAc into ManNAc and UDP, the first two steps in the sialic acid biosynthesis in mammals (Chou et al., ) and the first step of sialic acid (N‐acetylneuraminic acid) biosynthesis in bacteria (Murkin et al., ). UDP‐glucose 6‐dehydrogenase (UGD) has an indispensable role in hyaluronic acid capsule production and pathogenicity in Group A Streptococcus (Cole et al., ), is required for bacterial growth inside macrophages (Mouslim & Groisman, ). Undecaprenyl diphosphate synthase (UPPS) is involved in cell wall biosynthesis (peptidoglycan and wall teichoic acid synthesis) by catalyzing the synthesis of a polyisoprenoid, becoming an attractive antibacterial drug target (Farha et al., ).…”

Improvement of LysM-Mediated Surface Display of Designed Ankyrin Repeat Proteins (DARPins) in Recombinant and Nonrecombinant Strains of Lactococcus lactis and Lactobacillus Species

“…salivarius ATCC 11741 genome. UGDH can convert UDP-glucose to UDP-glucoronate, which is rarely observed in lactobacillus EPS (41) but is a relatively common constituent of the capsule of pathogenic Gram-positive bacteria (42,43). The interdependence of UDPglucoronate monomers in the EPS structure and LysM-mediated binding remains to be confirmed, and more detailed characterization is therefore needed to confirm the possible involvement of UGDH or the EPS structure.…”