Comparative study of the extracellular proteome of Sulfolobus species reveals limited secretion

Although a large number of potentially secreted proteins can be predicted on the basis of genomic distribution of signal sequence-bearing proteins, protein secretion in Archaea has barely been studied. A proteomic inventory and comparison of the growth medium proteins in three hyperthermoacidophiles, i.e., Sulfolobus solfataricus, S. acidocaldarius and S. tokodaii, indicates that only few proteins are freely secreted into the growth medium and that the majority originates from cell envelope bound forms. In S. acidocaldarius both cell-associated and secreted α-amylase activities are detected. Inactivation of the amyA gene resulted in a complete loss of activity, suggesting that the same protein is responsible for the a-amylase activity at both locations. It is concluded that protein secretion in Sulfolobus is a limited process, and it is suggested that the S-layer may act as a barrier for the free diffusion of folded proteins into the medium

1H, 13C, 15N backbone resonance assignments of the apo and holo forms of the ABC transporter solute binding protein PiuA from Streptococcus pneumoniae

Streptococcus pneumoniae is a Gram-positive human pathogen that causes millions of infections worldwide with an increasing occurrence of antibiotic resistance. Iron acquisition is essential for its survival and virulence, especially under host-imposed nutritional immunity. S. pneumoniae expresses several ATP-binding cassette (ABC) transporters to facilitate acquisition under iron limitation, including PitABCD, PiaABCD, and PiuBCDA. The substrate specificity of PiuBCDA is not fully established. Herein, we report the backbone 1H, 13C and 15N resonance assignments of the 31 kDa soluble, extracellular domain of the substrate binding protein PiuA in the apo form and in complex with Ga(III) and the catechol siderophore-mimic 4-LICAM. These studies provide valuable information for further functional studies of interactions with other proteins, metals, and small molecules

The Pneumococcal Iron Uptake Protein a (PiuA) Specifically Recognizes Tetradentate FeIIIbis- and Mono-Catechol Complexes

Streptococcus pneumoniae (Spn) is an important Gram-positive human pathogen that causes millions of infections worldwide with an increasing occurrence of antibiotic resistance. Fe acquisition is a crucial virulence determinant in Spn; further, Spn relies on exogenous FeIII-siderophore scavenging to meet nutritional Fe needs. Recent studies suggest that the human catecholamine stress hormone, norepinephrine (NE), facilitates Fe acquisition in Spn under conditions of transferrin-mediated Fe starvation. Here we show that the solute binding lipoprotein PiuA from the piu Fe acquisition ABC transporter PiuBCDA, previously described as an Fe-hemin binding protein, binds tetradentate catechol FeIII complexes, including NE and the hydrolysis products of enterobactin. Two protein-derived ligands (H238, Y300) create a coordinately-saturated FeIII complex, which parallel recent studies in the Gram-negative intestinal pathogen Campylobacter jejuni. Our in vitro studies using NMR spectroscopy and 54Fe LC-ICP-MS confirm the FeIII can move from transferrin to apo-PiuA in a NE-dependent manner. Structural analysis of PiuA FeIII-bis-catechol and GaIII-bis-catechol and GaIII-(NE)2 complexes by NMR spectroscopy reveals only localized structural perturbations in PiuA upon ligand binding, largely consistent with recent descriptions of other solute binding proteins of type II ABC transporters. We speculate that tetradentate FeIII complexes formed by mono- and bis-catechol species are important Fe sources in Gram-positive human pathogens, since PiuA functions in the same way as SstD from Staphylococcus aureus