| Summary: | <p>Abstract</p> <p>Background</p> <p>Glyceraldehyde 3-phosphate dehydrogenases (GAPDHs) are cytoplasmic glycolytic enzymes, which although lacking identifiable secretion signals, have also been found localized to the surface of several bacteria (and some eukaryotic organisms); where in some cases they have been shown to contribute to the colonization and invasion of host tissues. <it>Neisseria meningitidis </it>is an obligate human nasopharyngeal commensal which can cause life-threatening infections including septicaemia and meningitis. <it>N. meningitidis </it>has two genes, <it>gapA-1 </it>and <it>gapA-2</it>, encoding GAPDH enzymes. GapA-1 has previously been shown to be up-regulated on bacterial contact with host epithelial cells and is accessible to antibodies on the surface of capsule-permeabilized meningococcal cells. The aims of this study were: 1) to determine whether GapA-1 was expressed across different strains of <it>N. meningitidis</it>; 2) to determine whether GapA-1 surface accessibility to antibodies was dependant on the presence of capsule; 3) to determine whether GapA-1 can influence the interaction of meningococci and host cells, particularly in the key stages of adhesion and invasion.</p> <p>Results</p> <p>In this study, expression of GapA-1 was shown to be well conserved across diverse isolates of <it>Neisseria </it>species. Flow cytometry confirmed that GapA-1 could be detected on the cell surface, but only in a <it>siaD</it>-knockout (capsule-deficient) background, suggesting that GapA-1 is inaccessible to antibody in <it>in vitro</it>-grown encapsulated meningococci. The role of GapA-1 in meningococcal pathogenesis was addressed by mutational analysis and functional complementation. Loss of GapA-1 did not affect the growth of the bacterium <it>in vitro</it>. However, a GapA-1 deficient mutant showed a significant reduction in adhesion to human epithelial and endothelial cells compared to the wild-type and complemented mutant. A similar reduction in adhesion levels was also apparent between a <it>siaD</it>-deficient meningococcal strain and an isogenic <it>siaD gapA-1 </it>double mutant.</p> <p>Conclusions</p> <p>Our data demonstrates that meningococcal GapA-1 is a constitutively-expressed, highly-conserved surface-exposed protein which is antibody-accessible only in the absence of capsule. Mutation of GapA-1 does not affect the <it>in vitro </it>growth rate of <it>N. meningitidis</it>, but significantly affects the ability of the organism to adhere to human epithelial and endothelial cells in a capsule-independent process suggesting a role in the pathogenesis of meningococcal infection.</p>
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