The bacterial lung pathogen Streptococcus pneumoniae has a unique nutritional requirement for exogenous choline and attaches phosphorylcholine ( P -Cho) residues to the Gal p NAc moieties of its teichoic acids (TAs) in its cell wall. Two phosphorylcholine transferases, LicD1 and LicD2, mediate the attachment of P -Cho to the O-6 positions of the two Gal p NAc residues present in each repeating unit of pneumococcal TAs (pnTAs), of which only LicD1 has been determined to be essential. At the molecular level, the specificity of the P -Cho attachment to pnTAs by LicD1 and LicD2 remains still elusive. Here, using detailed structural analyses of pnTAs from a LicD2-deficient strain, we confirmed the specificity in the attachment of P -Cho residues to pnTA. LicD1 solely transfers P -Cho to α-d-Gal p NAc moieties, whereas LicD2 attaches P -Cho to β-d-Gal p NAc. Further, we investigated the role of the pneumococcal phosphorylcholine esterase (Pce) in the modification of the P -Cho substitution pattern of pnTAs. To clarify the specificity of Pce-mediated P -Cho hydrolysis, we evaluated different concentrations and pH conditions for the treatment of pneumococcal lipoteichoic acid with purified Pce. We show that Pce can hydrolyze both P -Cho residues of the terminal repeat of the pnTA chain and almost all P -Cho residues bound to β-d-Gal p NAc in vitro However, hydrolysis in vivo was restricted to the terminal repeat. In summary, our findings indicate that LicD1 and LicD2 specifically transfer P -Cho to α-d-Gal p NAc and β-d-Gal p NAc moieties, respectively, and that Pce removes distinct P -Cho substituents from pnTAs.
【저자키워드】 Bacteria, Streptococcus pneumoniae, cell wall, teichoic acid, nuclear magnetic resonance (NMR), Mass Spectrometry (MS), glycolipid structure, N-acetylgalactosamine, Phosphorylcholine esterase, Phosphorylcholine transferase,