Meningococcal surface fibril (Msf) binds to activated vitronectin and inhibits the terminal complement pathway to increase serum resistance

Abstract

SummaryComplement evasion is an important survival strategy of Neisseria meningitidis (Nm) during colonization and infection. Previously, we have shown that Nm Opc binds to serum vitronectin to inhibit complementmediated killing. In this study, we demonstrate meningococcal interactions with vitronectin via a novel adhesin, Msf (meningococcal surface fibril, previously NhhA or Hsf). As with Opc, Msf binds preferentially to activated vitronectin (aVn), engaging at its N-terminal region but the C-terminal heparin binding domain may also participate. However, unlike Opc, the latter binding is not heparin-mediated. By binding to aVn, Msf or Opc can impart serum resistance, which is further increased in coexpressers, a phenomenon dependent on serum aVn concentrations. The survival fitness of aVn-binding derivatives was evident from mixed population studies, in which msf/opc mutants were preferentially depleted. In addition, using vitronectin peptides to block Msf-aVn interactions, aVninduced inhibition of lytic C5b-9 formation and of serum killing could be reversed. As Msf-encoding gene is ubiquitous in the meningococcal strains examined and is expressed in vivo, serum resistance via Msf may be of significance to meningococcal pathogenesis. The data imply that vitronectin binding may be an important strategy for the in vivo survival of Nm for which the bacterium has evolved redundant mechanisms.

Comparative Proteome Analysis of Spontaneous Outer Membrane Vesicles and Purified Outer Membranes of Neisseria meningitidis

“…Among the OM proteins enriched in SOMVs, we found complement regulatory proteins fHbp, Opc, NspA, and NhhA (55,(58)(59)(60). Why does N. meningitidis sort complement regulatory proteins into SOMVs, although these proteins modulate complement activation on the bacterial surface?…”

Phase Variation Mediates Reductions in Expression of Surface Proteins during Persistent Meningococcal Carriage

“…These proteins have important primary functions-such as iron acquisition (e.g., HpuA, HmbR) and adhesion (e.g., Opc, NadA, and MspA) to host tissues-associated with their expression and hence phase-variants in an ON or high expression state are likely to contribute to survival on nasopharyngeal surfaces (20,21). Host persistence may be further facilitated by the secondary functions of some of these proteins; for example, Opc contributes to complement resistance (22,23). Selection for expression of the phenotypes associated with these SSCL is, therefore, potentially strong during host persistence.…”

Haemophilus influenzae surface fibril (Hsf) is a unique twisted hairpin-like trimeric autotransporter

“…A domain close to the C-terminal (2144-2315 aa) was constructed from PDB:3laa with low identity, but having a high local similarity. The remaining regions that were not matching with known threedimensional structures or had low identity/similarity to known templates were constructed as trimeric coiled coils (Griffiths et al, 2011). The trimeric models were first refined with Prime side chain prediction, and strained loops were refined using Prime loop prediction, followed by a constrained Prime energy refinement (imperf minimization).…”

“…Therefore, the 54-135 aa were not included in the model, and these amino acids will definitely contribute to the length of the fibril. In this model, however, only partial structures that have very poor template similarity were modeled as a coiled-coil as described elsewhere (Griffiths et al, 2011). The axial rise for an alpha-helical coiled coil is 1.5 Å per amino acid.…”

“…An in silico model of Hsf was constructed by using a comparative protein structure modeling on domains with a highly homologous amino acid sequence to that of a known three-dimensional structure determined by X-Ray Diffraction Crystallography. Domains with low homology to known three-dimensional structures was built as a trimeric coiled-coil as described elsewhere (Griffiths et al, 2011). The initial alignment from the BLAST/PSI-BLAST homology search was refined using ClustalW alignment and prime STA alignment combined with manual alignment.…”