Structural and biophysical characterization of the tandem substrate-binding domains of the ABC importer GlnPQ

Oxidation of hemoglobin in the lung parenchyma facilitates the differentiation of pneumococci into encapsulated bacteria

Pneumococcal pneumonia causes cytotoxicity in the lung parenchyma but the underlying mechanism involves multiple factors contributing to cell death. Here, we discovered that hydrogen peroxide produced by Streptococcus pneumoniae (Spn-H 2 O 2 ) plays a pivotal role by oxidizing hemoglobin, leading to its polymerization and subsequent release of labile heme. At physiologically relevant levels, heme selected a population of encapsulated pneumococci. In the absence of capsule and Spn-H 2 O 2 , host intracellular heme exhibited toxicity towards pneumococci, thus acting as an antibacterial mechanism. Further investigation revealed that heme-mediated toxicity required the ABC transporter GlnPQ. In vivo experiments demonstrated that pneumococci release H 2 O 2 to cause cytotoxicity in bronchi and alveoli through the non-proteolytic degradation of intracellular proteins such as actin, tubulin and GAPDH. Overall, our findings uncover a mechanism of lung toxicity mediated by oxidative stress that favor the growth of encapsulated pneumococci suggesting a therapeutic potential by targeting oxidative reactions.

Graphical abstract

Highlights

Oxidation of hemoglobin by Streptococcus pneumoniae facilitates differentiation to encapsulated pneumococci in vivo Differentiated S. pneumoniae produces capsule and hydrogen peroxide (Spn-H 2 O 2 ) as defense mechanism against host heme-mediated toxicity. Spn-H 2 O 2 -induced lung toxicity causes the oxidation and non-proteolytic degradation of intracellular proteins tubulin, actin, and GAPDH. The ABC transporter GlnPQ is a heme-binding complex that makes Spn susceptible to heme toxicity.

A new twist on PIFE: photoisomerisation-related fluorescence enhancement

PIFE was first used as an acronym for protein-induced fluorescence enhancement, which refers to the increase in fluorescence observed upon the interaction of a fluorophore, such as a cyanine, with a protein. This fluorescence enhancement is due to changes in the rate ofcis/transphotoisomerisation. It is clear now that this mechanism is generally applicable to interactions with any biomolecule. In this review, we propose that PIFE is thereby renamed according to its fundamental working principle as photoisomerisation-related fluorescence enhancement, keeping the PIFE acronym intact. We discuss the photochemistry of cyanine fluorophores, the mechanism of PIFE, its advantages and limitations, and recent approaches to turning PIFE into a quantitative assay. We provide an overview of its current applications to different biomolecules and discuss potential future uses, including the study of protein-protein interactions, protein-ligand interactions and conformational changes in biomolecules.

Biophysical Approaches for the Characterization of Protein-Metabolite Interactions

With an estimate of hundred thousands of protein molecules per cell and the number of metabolites several orders of magnitude higher, protein-metabolite interactions are omnipresent. In vitro analyses are one of the main pillars on the way to establish a solid understanding of how these interactions contribute to maintaining cellular homeostasis. A repertoire of biophysical techniques is available by which protein-metabolite interactions can be quantitatively characterized in terms of affinity, specificity, and kinetics in a broad variety of solution environments. Several of those provide information on local or global conformational changes of the protein partner in response to ligand binding. This review chapter gives an overview of the state-of-the-art biophysical toolbox for the study of protein-metabolite interactions. It briefly introduces basic principles, highlights recent examples from the literature, and pinpoints promising future directions.

Lactococcus lactis, an Attractive Cell Factory for the Expression of Functional Membrane Proteins

Membrane proteins play key roles in most crucial cellular processes, ranging from cell-to-cell communication to signaling processes. Despite recent improvements, the expression of functionally folded membrane proteins in sufficient amounts for functional and structural characterization remains a challenge. Indeed, it is still difficult to predict whether a protein can be overproduced in a functional state in some expression system(s), though studies of high-throughput screens have been published in recent years. Prokaryotic expression systems present several advantages over eukaryotic ones. Among them, Lactococcus lactis (L. lactis) has emerged in the last two decades as a good alternative expression system to E. coli. The purpose of this chapter is to describe L. lactis and its tightly inducible system, NICE, for the effective expression of membrane proteins from both prokaryotic and eukaryotic origins.

Fluorescence-based sensing of the bioenergetic and physicochemical status of the cell

Fluorescence-based sensors play a fundamental role in biological research. These sensors can be based on fluorescent proteins, fluorescent probes or they can be hybrid systems. The availability of a very large dataset of fluorescent molecules, both genetically encoded and synthetically produced, together with the structural insights on many sensing domains, allowed to rationally design a high variety of sensors, capable of monitoring both molecular and global changes in living cells or in in vitro systems. The advancements in the fluorescence-imaging field helped researchers to obtain a deeper understanding of how and where specific changes occur in a cell or in vitro by combining the readout of the fluorescent sensors with the spatial information provided by fluorescent microscopy techniques. In this review we give an overview of the state of the art in the field of fluorescent biosensors and fluorescence imaging techniques, and eventually guide the reader through the choice of the best combination of fluorescent tools and techniques to answer specific biological questions. We particularly focus on sensors for probing the bioenergetics and physicochemical status of the cell.