Structural Evidence of Perfluorooctane Sulfonate Transport by Human Serum Albumin

Perfluorooctane sulfonate (PFOS) is a man-made fluorosurfactant and globally persistent organic pollutant. PFOS is mainly distributed in blood with a long half-life for elimination. PFOS was found mainly bound to human serum albumin (HSA) in plasma, the most abundant protein in human blood plasma, which transports a variety of endogenous and exogenous ligands. However, the structural basis of such binding remains unclear. Here, we report the crystal structure of the HSA–PFOS complex and show that PFOS binds to HSA at a molar ratio of 2:1. In addition, PFOS binding renders the HSA structure more compact. Our results provide a structural mechanism to understand the retention of surfactants in human serum

Decrease in biofilm formation of the <i>nox</i> mutant with human plasma, extracellular matrix proteins and saliva.

<p>A, biofilm formation (OD₆₀₀) and growth (OD₄₅₀) in BM on plate wells pre-coated with human plasma and extracellular matrix proteins. B, biofilm formation (OD₆₀₀) in BM on plate wells pre-coated with human saliva (pre-coated) and in BM medium mixed with saliva (medium). (OD₄₅₀), growth in BM (pre-coated) or BM mixed with saliva (medium). Δ<i>nox</i>, the <i>nox</i> mutant; <i>Δnox_compl</i>, the complemented strain of the <i>nox</i> mutant. **, significant difference with P < 0.01 compared to SK36. Data obtained at least in triplicates.</p

Deduced mechanisms of the <i>nox</i> gene in relation to biofilm formation in <i>S</i>. <i>sanguinis</i>.

<p>Deletion of <i>nox</i> leads to cessation of the <i>nox</i>–mediated oxidation of NADH to NAD⁺. This causes decreased expression (green) of <i>ldh</i> and two genes encoding components of acetoin dehydrogenase, <i>acoA</i> and <i>acoB</i>, and increased expression (red) of <i>adhE</i>, <i>ackA</i>, <i>ald</i> and ethanolamine utilization genes including <i>eutG</i>, <i>eutE</i> and <i>pdu</i>. These gene expression changes affect the associated pathways to partially compensate for the imbalance of NAD⁺/NADH caused by <i>nox</i> deletion. Meanwhile, <i>gtfA</i> (red) expression increases and <i>gtfP</i> (green) expression decreases, which may cause more sucrose influx into energy metabolism rather than exopolysaccharide biosynthesis (e.g. glucan). Increased consumption of acetyl-CoA by AdhE may influence fatty acid biosynthesis to alter the membrane fatty acid components and to subsequently decrease the membrane fluidity and may suppress the release of eDNA. The inhibition of DNA release and glucan biosynthesis impairs biofilm matrix and results in defective biofilm formation. Green arrow, reduced reaction or function in the <i>nox</i> mutant; black arrow, normal reaction or function; red arrow, increased reaction or function; hollow arrow, function lost as a result of the <i>nox</i> deletion.</p

Change in membrane fluidity in the <i>nox</i> mutant.

<p>Δ<i>nox</i>, the <i>nox</i> mutant; <i>Δnox_compl</i>, the complemented strain of the <i>nox</i> mutant. *, significant difference with P < 0.05 compared to SK36. Data obtained at least in triplicates.</p

Comparison of fatty acid composition in the <i>nox</i> mutant and wild-type.

<p>Comparison of fatty acid composition in the <i>nox</i> mutant and wild-type.</p

NADH dehydrogenase activity of the rNox protein.

<p>Reduction of electron receptors by the rNox measured by spectrophotometrically monitoring the following wavelengths: FAD, 450 nm; DCIP, 600 nm; menadione, 340 nm; K₃(FeCN₃)₆, 420 nm; cytochrome c, 550 nm; CoQ₁₀, 340 nm; XTT, 480 nm. ***, P < 0.001. Data obtained at least in triplicates.</p

Change in eDNA concentration in the <i>nox</i> mutant.

<p>Δ<i>nox</i>, the <i>nox</i> mutant; <i>Δnox_compl</i>, the complemented strain of the <i>nox</i> mutant. *, significant difference with P < 0.05 compared to SK36. Data obtained at least in triplicates.</p

Biofilm and gene expressions changes of the <i>nox-</i>related mutants.

<p>A, biofilm structural comparison of the <i>ldh</i> mutant (left) and SK36 by confocal laser scanning microscopy. B, qRT-PCR for the expressions of <i>ldh</i> and <i>gtfP</i> genes in the <i>nox</i> mutant using <i>gyrA</i> as an internal control. C, biofilm decrease of the <i>gtfP</i> mutant (left). Δ<i>ldh</i>, the <i>ldh</i> mutant; Δ<i>nox</i>, the <i>nox</i> mutant; <i>Δnox_compl</i>, the complemented strain of the <i>nox</i> mutant; Δ<i>gtfP</i>, <i>gtfP</i> mutant; P-value significant difference in triplicates compared to SK36 *, P < 0.05; **, P < 0.01.</p

Reduction in biofilm formation in the <i>nox</i> mutant as assessed by confocal laser scanning microscopy.

<p>A, biofilm formation on a polystyrene surface detected using a confocal laser scanning microscope. B, quantification of biofilm formation in A. Δ<i>nox</i>, the <i>nox</i> mutant; <i>Δnox_compl</i>, the complemented strain of the <i>nox</i> mutant. **, significant difference with P < 0.01 between SK36 and <i>nox</i> mutant. Data obtained at least in triplicates.</p

DNA Molecular Beacon-Based Plastic Biochip: A Versatile and Sensitive Scanometric Detection Platform

In this paper, we report a novel DNA molecular beacon (MB)-based plastic biochip platform for scanometric detection of a range of analytical targets. Hairpin DNA strands, which are dually modified with amino and biotin groups at their two ends are immobilized on a disposable plastic (polycarbonate) substrate as recognition element and gold nanoparticle-assisted silver-staining as signal reading protocol. Initially, the immobilized DNA probes are in their folded forms; upon target binding the hairpin secondary structure of the probe strand is “forced” open (i.e., converted to the unfolded state). Nanogold-streptavidin conjugates can then bind the terminal biotin groups and promote the deposition of rather large silver particles which can be either directly visualized or quantified with a standard flatbed scanner. We demonstrate that with properly designed probe sequences and optimized preparation conditions, a range of molecular targets, such as DNA strands, proteins (thrombin) and heavy metal ions (Hg²⁺), can be detected with high sensitivity and excellent selectivity. The detection can be done in both standard physiological buffers and real world samples. This constitutes a platform technology for performing rapid, sensitive, cost-effective, and point-of-care (POC) chemical analysis and medical diagnosis