Structural and Thermodynamic Characterization of Metal Ion Binding in Streptococcus suis Dpr

Abstract

The use of protein cages for the creation of novel inorganic nanomaterials has attracted considerable attention in recent years. Ferritins are among the most commonly used protein cages in nanoscience. Accordingly, the binding of various metals to ferritins has been studied extensively. Dps (DNA-binding protein from starved cells)-like proteins belong to the ferritin superfamily. In contrast to ferritins, Dps-like proteins form 12-mers instead of 24-mers, have a different ferroxidase center, and are able to store a smaller amount of iron atoms in a hollow cavity (up to ∼500, instead of the ∼4500 iron atoms found in ferritins). With the exception of iron, the binding of other metal cations to Dps proteins has not been studied in detail. Here, the binding of six divalent metal ions (Zn(2+), Mn(2+), Ni(2+), Co(2+), Cu(2+), and Mg(2+)) to Streptococcus suisDps-like peroxide resistance protein (SsDpr) was characterized by X-ray crystallography and isothermal titration calorimetry (ITC). All metal cations, except for Mg(2+), were found to bind to the ferroxidase center similarly to Fe(2+), with moderate affinity (binding constants between 0.1×10(5) M(-1) and 5×10(5) M(-1)). The stoichiometry of binding, as deduced by ITC data, suggested the presence of a dication ferroxidase site. No other metal binding sites were identified in the protein. The results presented here demonstrate the ability of SsDpr to bind various metals as substitutes for iron and will help in better understanding protein-metal interactions in the Dps family of proteins as potential metal nanocontainers.

Effect of Nonheme Iron-Containing Ferritin Dpr in the Stress Response and Virulence of Pneumococci

“…dpr was first discovered by a library screening for a gene(s) responsible for resistance to peroxide or hydroperoxide toxicity in S. mutans (11). Dpr belongs to the Dps member family and has a structure similar to that of either ferritin or Dps (14,15,(38)(39)(40). Studies have showed that dpr serves to protect Gram-positive bacteria against oxidative and other stresses (11)(12)(13).…”

“…A homolog of Dps, Dpr (Dps-like peroxide resistance), is conserved in Gram-positive bacteria, such as Streptococcus mutans, Streptococcus pyogenes, and Streptococcus suis (11)(12)(13). The structure of Dpr from S. suis is similar to that of Dps, and it can bind ferrous ions as well as other divalent cations, such as Cu 2ϩ , Mn 2ϩ , and Zn 2ϩ (14,15). Dpr is essential for aerobic survival of S. mutans and also prevents iron-dependent hydroxyl radical formation in vitro (16).…”

Stress Physiology of Lactic Acid Bacteria

“…Although the oxidative stress response has been researched extensively in LAB, the regulatory mechanisms involved are still largely unknown (92) (97), and it plays a key role in aerobic growth of S. mutans (98) and S. suis (99). PmtA is a putative Zn 2ϩ efflux transporter, and its overexpression resulted in a strong induction of the AdcR-regulated genes (see the section on the MarR family, above) (95).…”

Conserved histidine residues at the ferroxidase centre of the Campylobacter jejuni Dps protein are not strictly required for metal binding and oxidation

“…It has been previously reported that Mn 2+ can bind to the FOC of Dps (Ardini et al, 2013), which is expected as Fe 2+ and Mn 2+ can assume similar coordination geometries in protein crystal structures (Haikarainen et al, 2011;Zheng et al, 2008). We evaluated the binding of manganese to CjDps by measuring the intrinsic tryptophan fluorescence (Fig.…”

“…In addition to Fe 2+ , some Dps members are able to bind other metal ions (Havukainen et al, 2008;Yokoyama & Fujii, 2014). The Streptococcus suis Dps can bind Cu 2+ , Ni 2+ , Co 2+ and Mn 2+ to the FOC, as determined by isothermal titration calorimetry and X-ray crystallography (Haikarainen et al, 2011). Furthermore, Kineococcus radiotolerans Dps can form an Mn-Fe heteronuclear metal cluster at the FOC; however, only iron can be stored inside the protein shell (Ardini et al, 2013).…”