The crystal structure of pneumococcal surface antigen PsaA reveals a metal-binding site and a novel structure for a putative ABC-type binding protein

Abstract

. The structural topology of PsaA is fundamentally different from that of other ABC-type binding proteins determined thus far in that PsaA lacks the characteristic 'hinge peptides' involved in conformational change upon solute uptake and release. In our structure, the metal-binding site is probably occupied by Zn2+. The site seems to be well conserved amongst related receptors from both Gram-positive and Gram-negative bacteria.

Structure and metal binding properties of ZnuA, a periplasmic zinc transporter from Escherichia coli

“…The structural and biochemical data presented here combined with previous reports [7,10,11,15,19] provide insight into the mechanism of metal acquisition and transport by Eco-ZnuA. The binding of Zn 2+ in the main metal binding site of apoZnuA probably results in local conformational changes in the loop that houses ligands Glu59 and His60 (Fig.…”

“…Metal-bound structures of Syn-ZnuA [7], Streptococcus pneumoniae PsaA (Spn-PsaA) [10], Treponema pallidum TroA (Tpa-TroA) [11], Synechocystis PCC sp. 6803 MntC (Syn-MntC) [12], and Eco-ZnuA [13,14] as well as the metal-free (apo) structures of Tpa-TroA [15] and mutant Syn-ZnuA (without the His-rich loop) [8] have been determined by X-ray crystallography.…”

“…Although the structures of Spn-PsaA [10] and Tpa-TroA [11] both contain Zn 2+ , the physiological ligand for these proteins is likely Mn 2+ [2]. The in vitro metal binding affinities of Tpa-TroA for Zn 2+ and Mn 2+ are similar, with K d values of 1.27 and 0.95 μM, respectively [19]; that of Syn-ZnuA is substantially higher, approximately 10 nM [8].…”

Interactions between TonB from Escherichia coli and the Periplasmic Protein FhuD

“…The overall fold of FhuD is similar to that of BtuF (14,15), the periplasmic cobalamin-binding protein of E. coli. Periplasmic metal-binding proteins TroA (16) and PsaA (17) are also structurally related to FhuD. These proteins share a fold distinct from those of classical periplasmic proteins such as maltose-binding protein (18).…”

Crystal Structures of the Liganded and Unliganded Nickel-binding Protein NikA from Escherichia coli

“…The crystal structures of two metal binding proteins in the solute-binding protein family, however, show a very different connection between the two domains, forming a new family of metal binding receptors (24). TroA is a zinc-binding protein from Treponema pallidum (25,26), and PsaA is a manganese/zinc-binding protein from Streptococcus pneumoniae (27). In these proteins, the polypeptide chain passes from one domain to the other only once, this connection being a long helix running most of the length of the protein.…”