An Outer Membrane Receptor of Neisseria meningitidis Involved in Zinc Acquisition with Vaccine Potential

Michiel Stork,Vincent E Weynants,Jan T Poolman,Ilse Jongerius,Natasja De Kok,Ingrid Schilders,Martine P Bos,Jan Tommassen,H Steven Seifert

doi:10.1371/journal.ppat.1000969

Michiel Stork, Vincent E Weynants + Show 7 more

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https://doi.org/10.1371/journal.ppat.1000969

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Journal: PLoS Pathogens	Publication Date: Jul 1, 2010
Citations: 155	License type: CC BY 4.0

Affiliation: Utrecht University, GlaxoSmithKline (Belgium)

Abstract

Since the concentration of free iron in the human host is low, efficient iron-acquisition mechanisms constitute important virulence factors for pathogenic bacteria. In Gram-negative bacteria, TonB-dependent outer membrane receptors are implicated in iron acquisition. It is far less clear how other metals that are also scarce in the human host are transported across the bacterial outer membrane. With the aim of identifying novel vaccine candidates, we characterized in this study a hitherto unknown receptor in Neisseria meningitidis. We demonstrate that this receptor, designated ZnuD, is produced under zinc limitation and that it is involved in the uptake of zinc. Upon immunization of mice, it was capable of inducing bactericidal antibodies and we could detect ZnuD-specific antibodies in human convalescent patient sera. ZnuD is highly conserved among N. meningitidis isolates and homologues of the protein are found in many other Gram-negative pathogens, particularly in those residing in the respiratory tract. We conclude that ZnuD constitutes a promising candidate for the development of a vaccine against meningococcal disease for which no effective universal vaccine is available. Furthermore, the results suggest that receptor-mediated zinc uptake represents a novel virulence mechanism that is particularly important for bacterial survival in the respiratory tract.

Highlights

The cell envelope of Gram-negative bacteria consists of two membranes, the inner and the outer membrane, which are separated by the periplasm containing the peptidoglycan layer
We show that expression of this receptor is induced under zinc limitation and that the protein is involved in the uptake of zinc. Homologues of this protein are present in many other Gram-negative pathogens, in those residing in the respiratory tract, suggesting that receptor-mediated zinc acquisition is important for bacteria residing in this niche
We found that the protein is highly conserved among N. meningitidis isolates and that it induces bactericidal antibodies upon immunization of mice

Summary

Introduction

The cell envelope of Gram-negative bacteria consists of two membranes, the inner and the outer membrane, which are separated by the periplasm containing the peptidoglycan layer. The outer membrane forms a barrier for harmful compounds from the environment. Most nutrients can pass the outer membrane by passive diffusion via abundant channel-forming outer membrane proteins, collectively called porins. Diffusion is not an option when the extracellular concentration of a nutrient is low. This is usually the case, for example, with iron. Pathogens are confronted with low concentrations of free iron within the human host, where iron is bound by iron-transport and -storage proteins, such as lactoferrin and transferrin. Efficient iron acquisition mechanisms constitute important virulence factors and have been studied extensively in many pathogens [1,2]

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