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Published November 7, 2014 | Published
Journal Article Open

The Interaction of N-Glycans in Fcγ Receptor I α-Chain with Escherichia coli K1 Outer Membrane Protein A for Entry into Macrophages

Abstract

Neonatal meningitis, caused by Escherichia coli K1, is a serious central nervous system disease. We have established that macrophages serve as permissive niches for E. coli K1 to multiply in the host and for attaining a threshold level of bacterial load, which is a prerequisite for the onset of the disease. Here, we demonstrate experimentally that three N-glycans in FcγRIa interact with OmpA of E. coli K1 for binding to and entering the macrophages. Adoptive transfer of FcγRIa−/− bone marrow-derived macrophages transfected with FcγRIa into FcγRIa−/− newborn mice renders them susceptible to E. coli K1-induced meningitis. In contrast, mice that received bone marrow-derived macrophages transfected with FcγRIa in which N-glycosylation sites 1, 4, and 5 are mutated to alanines exhibit resistance to E. coli K1 infection. Our molecular dynamics and simulation studies predict that N-glycan 5 exhibits strong binding at the barrel site of OmpA formed by loops 3 and 4, whereas N-glycans 1 and 4 interact with loops 1, 3, and 4 of OmpA at tip regions. Molecular modeling data also suggest no role for the IgG binding site in the invasion process. In agreement, experimental mutations in IgG binding site had no effect on the E. coli K1 entry into macrophages in vitro or on the onset of meningitis in newborn mice. Together, this integration of experimental and computational studies reveals how the N-glycans in FcγRIa interact with the OmpA of E. coli K1 for inducing the disease pathogenesis.

Additional Information

© 2014 The American Society for Biochemistry and Molecular Biology. Received August 4, 2014; accepted September 17, 2014. First Published on September 17, 2014. We thank Rahul Mittal for helping in scanning and transmission electron microscopy using University of Southern California School of Medicine core facilities. This work was supported by NIH grants NS73115 and AI40567 to NVP (PI) and WAG (Co-PI). The computational studies were carried out on computers in the WAG lab provided by DURIP and NSF CSEM.

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