Cell Surface Antigen – Manganese‐Binding ProteinMntCfromStaphylococcus Aureus

Abstract

MntC is the metal‐binding protein component of the Mn 2+ ‐specific MntABC transporter from the human pathogen Staphylococcus aureus . MntC orthologs are found in all Gram positive bacteria, the protein is attached to the bacterial membrane through a lipid anchor and captures Mn 2+ ion from the environment with high affinity for subsequent transport across the transmembrane channel of the transporter. MntC consists of two homologous domains connected through a long ‘backbone’ α‐helix, with a metal‐binding site located at the interface of those domains. The long α‐helix restricts domain mobility, making it harder for the bound ligand (Mn 2+ ) to escape the binding site and, correspondingly, increasing the metal‐binding affinity of the protein. The physiological role of Mn 2+ binding by MntC in bacterial resistance to oxidative stress is well documented. MntC is also able to bind other divalent metals (Zn 2+ , Co 2+ , Ni 2+ , and Cd 2+ ), although it is not yet clear whether this has any biological relevance. Binding of divalent metals to the protein can be reversible and irreversible, depending on the nature of the metal. X‐ray data provide a plausible explanation for the two binding modes: the X‐ray structure contains two molecules in the asymmetric unit, with the metal‐binding site being solvent accessible in one molecule and inaccessible in the other. Serum antibodies to MntC (or orthologs of MntC) are detected following exposure to staphylococcal species in animal models as well as in human sera from patients with S. aureus infections. Immunization with a recombinant expressed MntC protein antigen induces protective immunity against S. aureus in preclinical models of infection. As such, MntC is a promising vaccine candidate and is currently being tested in human clinical trials as a component of a multiantigen vaccine for the prevention of staphylococcal infections.

Biochemical and Spectroscopic Observation of Mn(II) Sequestration from Bacterial Mn(II) Transport Machinery by Calprotectin

“…4 In the current work, performed to provide molecular understanding of the tug-of-war between CP and microbes for Mn(II), we employ biochemical and electron paramagnetic resonance (EPR) spectroscopic methods to evaluate metal competition between human CP and bacterial metal transport machinery. We focus on extracellular solute-binding proteins (SBPs) employed by two Gram-positive human pathogens for acquiring Mn(II) from the host, MntC of S. aureus 5 and PsaA of Streptococcus pneumoniae . 6 The results show that CP outcompetes both of these Mn(II)-acquisition proteins for Mn(II) under conditions of high Ca(II), as found in the extracellular environment.…”

High-Field EPR Spectroscopic Characterization of Mn(II) Bound to the Bacterial Solute-Binding Proteins MntC and PsaA

“…The crystallographic Mn(II)-MntC site was described as 5coordinate where His50, His123, Oε1 of Glu189, and both Oδ1 and Oδ2 of Asp264 coordinate the metal ion (Figure 1B). 14 However, the metal-ligand distances determined crystallographically range from 2.1-2.8 Å and do not preclude the possibility of other coordination geometries (Figure 1). In addition, the metal content of the crystallized protein is ambiguous because the protein in solution contained low amounts of various metal ions according to inductively-coupled mass spectrometry and anomalous diffraction data was not reported, 14 which can be employed to confirm the identity of the bound metal.…”

“…14 However, the metal-ligand distances determined crystallographically range from 2.1-2.8 Å and do not preclude the possibility of other coordination geometries (Figure 1). In addition, the metal content of the crystallized protein is ambiguous because the protein in solution contained low amounts of various metal ions according to inductively-coupled mass spectrometry and anomalous diffraction data was not reported, 14 which can be employed to confirm the identity of the bound metal. As a result, the Mn(II) coordination sphere of MntC is not well-defined and requires further examination.…”

“…[11][12][13] How MntC and PsaA coordinate Mn(II) and deliver it to their respective permease has not been fully elucidated. Reported crystal structures of Mn(II)-MntC (2.2-Å resolution) 14 and Mn(II)-PsaA (2.7-Å resolution) 15 show Mn(II) bound by a His 2 AspGlu coordination sphere in both proteins (Figure 1). The crystallographic Mn(II)-MntC site was described as 5coordinate where His50, His123, Oε1 of Glu189, and both Oδ1 and Oδ2 of Asp264 coordinate the metal ion (Figure 1B).…”

“…The spectral data and simulations indicate that MntC and PsaA both bind Mn(II) in a similar tetrahedral or trigonal prismatic coordination environment consistent with the primary coordination sphere defined by the His 2 AspGlu motifs observed crystallographically. [14][15]17…”