Lipopolysaccharide-linked Enterobacterial Common Antigen (ECA_LPS) Occurs in Rough Strains of <i>Escherichia coli</i> R1, R2, and R4

• Main Authors: Anna Maciejewska, Marta Kaszowska, Wojciech Jachymek, Czeslaw Lugowski, Jolanta Lukasiewicz
• Format: Article
• Language: English
• Published: MDPI AG 2020-08-01
• Series: International Journal of Molecular Sciences
• Subjects: enterobacterial common antigen; ECA; lipopolysaccharide; LPS; ECA_LPS; endotoxin
• Online Access: https://www.mdpi.com/1422-0067/21/17/6038

Enterobacterial common antigen (ECA) is a conserved surface antigen characteristic for <i>Enterobacteriaceae</i>. It is consisting of trisaccharide repeating unit, →3)-α-D-Fuc<i>p</i>4NAc-(1→4)-β-D-Man<i>p</i>NAcA-(1→4)-α-D-Glc<i>p</i>NAc-(1→, where prevailing forms include ECA linked to phosphatidylglycerol (ECA_PG) and cyclic ECA (ECA_CYC). Lipopolysaccharide (LPS)-associated form (ECA_LPS) has been proved to date only for rough <i>Shigella sonnei</i> phase II. Depending on the structure organization, ECA constitutes surface antigen (ECA_PG and ECA_LPS) or maintains the outer membrane permeability barrier (ECA_CYC). The existence of LPS was hypothesized in the 1960-80s on the basis of serological observations. Only a few <i>Escherichia coli</i> strains (i.e., R1, R2, R3, R4, and K-12) have led to the generation of anti-ECA antibodies upon immunization, excluding ECA_PG as an immunogen and conjecturing ECA_LPS as the only immunogenic form. Here, we presented a structural survey of ECA_LPS in <i>E. coli</i> R1, R2, R3, and R4 to correlate previous serological observations with the presence of ECA_LPS. The low yields of ECA_LPS were identified in the R1, R2, and R4 strains, where ECA occupied outer core residues of LPS that used to be substituted by O-specific polysaccharide in the case of smooth LPS. Previously published observations and hypotheses regarding the immunogenicity and biosynthesis of ECA_LPS were discussed and correlated with presented herein structural data.