The Interaction of N-glycans in Fc-gamma Receptor I Alpha Chain with Escherichia coli K1 Outer Membrane Protein A for Entry into Macrophages — Experimental and Computational Analysis [Molecular Bases of Disease]

September 17th, 2014 by Krishnan, S., Liu, F., Abrol, R., Hodges, J., Goddard, W. A., Prasadarao, N. V.

Neonatal meningitis, due to 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 pre-requisite 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 (BMDMs) transfected with FcγRIa into FcγRIa-/- newborn mice renders them susceptible to E. coli K1-induced meningitis. In contrast, mice that received BMDMs 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 while N-glycans 1 and 4 interact with the loops of 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.
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