Zinc sequestration by human calprotectin facilitates manganese binding to the bacterial solute-binding proteins PsaA and MntC

Abstract

Zinc is an essential transition metal nutrient for bacterial survival and growth but may become toxic when present at elevated levels. The Gram-positive bacterial pathogen Streptococcus pneumoniae is sensitive to zinc poisoning, which results in growth inhibition and lower resistance to oxidative stress. S. pneumoniae has a relatively high manganese requirement and zinc toxicity in this pathogen has been attributed to the coordination of Zn(II) at the Mn(II) site of the solute-binding protein (SBP) PsaA, which prevents Mn(II) uptake by the PsaABC transport system. In this work, we investigate the Zn(II)-binding properties of pneumococcal PsaA and staphylococcal MntC, a related SBP expressed by another Gram-positive bacterial pathogen, Staphylococcus aureus, that contributes to Mn(II) uptake. X-ray absorption spectroscopic studies demonstrate that both SBPs harbor Zn(II) sites best described as five-coordinate, and metal-binding studies in solution show that both SBPs bind Zn(II) reversibly with sub-nanomolar affinities. Moreover, both SBPs exhibit a strong thermodynamic preference for Zn(II) ions, which readily displace bound Mn(II) ions from these proteins. We also evaluate the Zn(II) competition between these SBPs and the human S100 protein calprotectin (CP, S100A8/S100A9 oligomer), an abundant host-defense protein that is involved in the metal-withholding innate immune response. CP can sequester Zn(II) from PsaA and MntC, which facilitates Mn(II) binding to the SBPs. These results demonstrate that CP can inhibit Zn(II) poisoning of the SBPs and provide molecular insight into how S100 proteins may inadvertently benefit bacterial pathogens rather than the host.

Metalloproteomics: Unraveling the Metal Binding Proteins of Diverse Metal-Resistant Bacteria

“…Zinc-binding proteins: Several studies have investigated the binding properties of these proteins and their impact on bacterial survival. In 2022, Rosen et al [69] demonstrated that the solute-binding proteins (SBPs) called PsaA and MntC in Streptococcus pneumoniae and Staphylococcus aureus, respectively, bind Zn reversibly and exhibit a preference for Zn ions over other metals. Researchers have uncovered several mechanisms by which bacteria resist zinc toxicity.…”

Remodeling of Paranasal Sinuses Mucosa Functions in Response to Biofilm-Induced Inflammation

“…196 Interestingly, by reducing sensitivity to zinc poisoning, CP may inadvertently benefit bacterial pathogens instead of the host, eg, via sequestration of Zn from high-affinity manganese transporter PsaA of highly sensitive to zinc poisoning pathogen S. pneumoniae. 197 Finally, production of high-affinity Zn transporter ZnuABC transporter allows Salmonella enterica to overcome CP-mediated Zn sequestration, and, in turn, to outcompete intestinal commensals and survive in the inflamed intestine. 76…”

The oxidative stress response of Streptococcus pneumoniae: its contribution to both extracellular and intracellular survival

“…The proposed mechanism involves the displacement of Mn 2+ by Zn 2+ in the PsaA protein, thereby hindering the uptake of Mn 2+ and resulting in a deficiency of this cation within the cytoplasm ( Jacobsen et al, 2011 ; Counago et al, 2014 ). Nevertheless, throughout the course of pneumococcal infection, both CP ( Rosen et al, 2022 ) and calgranulin ( Rosen and Nolan, 2022 ) have the ability to sequester Zn 2+ from PsaA, facilitating the binding of Mn 2+ to this protein and subsequent uptake of Mn 2+ . Interestingly, these proteins, which are employed by host cells as antimicrobial agents, paradoxically promote bacterial pathogenesis in this particular context.…”