TY - JOUR
T1 - Genetic and biochemical modulation of sialic acid O-acetylation on group B Streptococcus
T2 - Phenotypic and functional impact
AU - Weiman, Shannon
AU - Dahesh, Samira
AU - Carlin, Aaron F.
AU - Varki, Ajit
AU - Nizet, Victor
AU - Lewis, Amanda L.
N1 - Funding Information:
The UC President’s Postdoctoral Fellowship Program (AL); the Gianinni Family Foundation (AL); and National Institutes of Health grants R01-HD051796 (VN) and P01-HL057345 (AV).
PY - 2009
Y1 - 2009
N2 - Group B Streptococcus (GBS) is an important human pathogen and a model system for studying the roles of bacterial glycosylation in host-microbe interactions. Sialic acid (Sia), expressed prominently in the GBS capsular polysaccharide (CPS), mimics mammalian cell surface Sia and can interact with host Sia-binding proteins to subvert immune clearance mechanisms. Our earlier work has shown that GBS partially O-acetylates CPS Sia residues and employs an intracellular O-acetylation/ de-O-acetylation cycle to control the final level of this surface Sia modification. Here, we examine the effects of point mutations in the NeuD O-acetyltransferase and NeuA O-acetylesterase on specific glycosylation phenotypes of GBS, pinpointing an isogenic strain pair that differs dramatically in the degree of the O-acetyl modification (80% versus 5%) while still expressing comparable levels of overall sialylation. Using these strains, higher levels of O-acetylation were found to protect GBS CPS Sia against enzymatic removal by microbial sialidases and to impede engagement of human Siglec-9, but not to significantly alter the ability of GBS to restrict complement C3b deposition on its surface. Additional experiments demonstrated that pH-induced migration of the O-acetyl modification from the 7- to 9-carbon position had a substantial impact on GBS-Siglec-9 interactions, with 7-O-acetylation exhibiting the strongest interference. These studies show that both the degree and position of the GBS O-acetyl modification influence Sia-specific interactions relevant to the host-pathogen relationship. We conclude that native GBS likely expresses a phenotype of intermediate Sia O-acetylation to strike a balance between competing selective pressures present in the host environment.
AB - Group B Streptococcus (GBS) is an important human pathogen and a model system for studying the roles of bacterial glycosylation in host-microbe interactions. Sialic acid (Sia), expressed prominently in the GBS capsular polysaccharide (CPS), mimics mammalian cell surface Sia and can interact with host Sia-binding proteins to subvert immune clearance mechanisms. Our earlier work has shown that GBS partially O-acetylates CPS Sia residues and employs an intracellular O-acetylation/ de-O-acetylation cycle to control the final level of this surface Sia modification. Here, we examine the effects of point mutations in the NeuD O-acetyltransferase and NeuA O-acetylesterase on specific glycosylation phenotypes of GBS, pinpointing an isogenic strain pair that differs dramatically in the degree of the O-acetyl modification (80% versus 5%) while still expressing comparable levels of overall sialylation. Using these strains, higher levels of O-acetylation were found to protect GBS CPS Sia against enzymatic removal by microbial sialidases and to impede engagement of human Siglec-9, but not to significantly alter the ability of GBS to restrict complement C3b deposition on its surface. Additional experiments demonstrated that pH-induced migration of the O-acetyl modification from the 7- to 9-carbon position had a substantial impact on GBS-Siglec-9 interactions, with 7-O-acetylation exhibiting the strongest interference. These studies show that both the degree and position of the GBS O-acetyl modification influence Sia-specific interactions relevant to the host-pathogen relationship. We conclude that native GBS likely expresses a phenotype of intermediate Sia O-acetylation to strike a balance between competing selective pressures present in the host environment.
KW - Capsular polysaccharide
KW - N-acetylneuraminic acid
KW - Sialidase
KW - Siglec
KW - Streptococcus agalactiae
UR - http://www.scopus.com/inward/record.url?scp=70350003969&partnerID=8YFLogxK
U2 - 10.1093/glycob/cwp111
DO - 10.1093/glycob/cwp111
M3 - Article
C2 - 19643844
AN - SCOPUS:70350003969
VL - 19
SP - 1204
EP - 1213
JO - Glycobiology
JF - Glycobiology
SN - 0959-6658
IS - 11
ER -