Effects of zero-valent iron added in the flooding or drainage process on cadmium immobilization in an acid paddy soil.

Zero-valent iron (ZVI) is a promising material for the remediation of Cd-contaminated paddy soils. However, the effects of ZVI added during flooding or drainage processes on cadmium (Cd) retention remain unclear. Herein, Cd-contaminated paddy soil was incubated for 40 days of flooding and then for 15 days of drainage, and the underlying mechanisms of Cd immobilization coupled with Fe/S/N redox processes were investigated. The addition of ZVI to the flooding process was more conducive to Cd immobilization. Less potential available Cd was detected by adding ZVI before flooding, which may be due to the increase in paddy soil pH and newly formed secondary Fe minerals. Moreover, the reductive dissolution of Fe minerals promoted the release of soil colloids, thereby increasing significantly the surface sites and causing Cd immobilization. Additionally, the addition of ZVI before flooding played a vital role in Cd retention after soil drainage. In contrast, the addition of ZVI in the drainage phase was not conducive to Cd retention, which might be due to the rapid decrease in soil pH that inhibited Cd adsorption and further immobilization on soil surfaces. The findings of this study demonstrated that Cd availability in paddy soil was largely reduced by adding ZVI during the flooding period and provide a novel insight into the mechanisms of ZVI remediation in Cd-contaminated paddy soils.

Iron Vacancy Accelerates Fe(II)-Induced Anoxic As(III) Oxidation Coupled to Iron Reduction.

Chemical oxidation of As(III) by iron (Fe) oxyhydroxides has been proposed to occur under anoxic conditions and may play an important role in stabilization and detoxification of As in subsurface environments. However, this reaction remains controversial due to lack of direct evidence and poorly understood mechanisms. In this study, we show that As(III) oxidation can be facilitated by Fe oxyhydroxides (i.e., goethite) under anoxic conditions coupled with the reduction of structural Fe(III). An excellent electron balance between As(V) production and Fe(III) reduction is obtained. The formation of an active metastable Fe(III) phase at the defective surface of goethite due to atom exchange is responsible for the oxidation of As(III). Furthermore, the presence of defects (i.e., Fe vacancies) in goethite can noticeably enhance the electron transfer (ET) and atom exchange between the surface-bound Fe(II) and the structural Fe(III) resulting in a two time increase in As(III) oxidation. Atom exchange-induced regeneration of active goethite sites is likely to facilitate As(III) coordination and ET with structural Fe(III) based on electrochemical analysis and theoretical calculations showing that this reaction pathway is thermodynamically and kinetically favorable. Our findings highlight the synergetic effects of defects in the Fe crystal structure and Fe(II)-induced catalytic processes on anoxic As(III) oxidation, shedding a new light on As risk management in soils and subsurface environments.

PCSK9 Inhibition: From Current Advances to Evolving Future.

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a secretory serine protease synthesized primarily by the liver. It mainly promotes the degradation of low-density lipoprotein receptor (LDL-R) by binding LDL-R, reducing low-density lipoprotein cholesterol (LDL-C) clearance. In addition to regulating LDL-R, PCSK9 inhibitors can also bind Toll-like receptors (TLRs), scavenger receptor B (SR-B/CD36), low-density lipoprotein receptor-related protein 1 (LRP1), apolipoprotein E receptor-2 (ApoER2) and very-low-density lipoprotein receptor (VLDL-R) reducing the lipoprotein concentration and slowing thrombosis. In addition to cardiovascular diseases, PCSK9 is also used in pancreatic cancer, sepsis, and Parkinson's disease. Currently marketed PCSK9 inhibitors include alirocumab, evolocumab, and inclisiran, as well as small molecules, nucleic acid drugs, and vaccines under development. This review systematically summarized the application, preclinical studies, safety, mechanism of action, and latest research progress of PCSK9 inhibitors, aiming to provide ideas for the drug research and development and the clinical application of PCSK9 in cardiovascular diseases and expand its application in other diseases.

Distinct roles of pH and organic ligands in the dissolution of goethite by cysteine.

Electron shuttles such cysteine play an important role in Fe cycle and its availability in soils, while the roles of pH and organic ligands in this process are poorly understood. Herein, the reductive dissolution process of goethite by cysteine were explored in the presence of organic ligands. Our results showed that cysteine exhibited a strong reactivity towards goethite - a typical iron minerals in paddy soils with a rate constant ranging from 0.01 to 0.1 hr-1. However, a large portion of Fe(II) appeared to be "structural species" retained on the surface. The decline of pH was favorable to generate more Fe(II) ions and enhancing tendency of Fe(II) release to solution. The decline of generation of Fe(II) by increasing pH was likely to be caused by a lower redox potential and the nature of cysteine pH-dependent adsorption towards goethite. Interestingly, the co-existence of oxalate and citrate ligands also enhanced the rate constant of Fe(II) release from 0.09 to 0.15 hr-1; nevertheless, they negligibly affected the overall generation of Fe(II) in opposition to the pH effect. Further spectroscopic evidence demonstrated that two molecules of cysteine could form disulfide bonds (S-S) to generate cystine through oxidative dehydration, and subsequently, inducing electron transfer from cysteine to the structural Fe(III) on goethite; meanwhile, those organic ligands act as Fe(II) "strippers". The findings of this work provide new insights into the understanding of the different roles of pH and organic ligands on the generation and release of Fe induced by electron shuttles in soils.

New insights into stoichiometric efficiency and synergistic mechanism of persulfate activation by zero-valent bimetal (Iron/Copper) for organic pollutant degradation.

Extensive studies have been devoting to investigating the catalytic efficiency of zero-valent iron (Fe0)-based bimetals with persulfate (PS), while little is known in the stoichiometric efficiency, underlying mechanisms and reaction center of zero-valent bimetallic catalysts in activating PS. Herein, nanoscale zero-valent Fe/Cu catalysts in decomposing 2,4-dichlorophenol (DCP) have been investigated. The results show that the increase of Cu ratio from 0 to 0.75 significantly enhances the DCP degradation with a rate constant of 0.025 min-1 for Fe0 to 0.097 min-1 for Fe/Cu(0.75) at pH ∼3.3, indicating Cu is likely the predominate reaction centers over Fe. The PS decomposition is reduced with the increase of Cu ratios, suggesting the stoichiometric efficiency of Fe/Cu in activating PS is notably enhanced from 0.024 for Fe0 to 0.11 for Fe/Cu(0.75). Analyses indicate Cu atoms are likely the predominant reaction site for DCP decomposition, and Fe atoms synergistically enhance the activity of Cu as indicated by DFT calculations. Both SO4⦁- and ⦁OH radicals are responsible for reactions, and the contribution of SO4⦁- is decreased at higher pH conditions. The findings of this work provide insight into the stoichiometric efficiency and the reaction center of Fe/Cu catalysts to activate PS for pollutant removals.

Inhibition of an active zymogen protease: the zymogen form of matriptase is regulated by HAI-1 and HAI-2.

The membrane-bound serine protease matriptase belongs to a rare subset of serine proteases that display significant activity in the zymogen form. Matriptase is critically involved in epithelial differentiation and homeostasis, and insufficient regulation of its proteolytic activity directly causes onset and development of malignant cancer. There is strong evidence that the zymogen activity of matriptase is sufficient for its biological function(s). Activated matriptase is inhibited by the two Kunitz-type inhibitor domain-containing hepatocyte growth factor activator inhibitors 1 (HAI-1) and HAI-2, however, it remains unknown whether the activity of the matriptase zymogen is regulated. Using both purified proteins and a cell-based assay, we show that the catalytic activity of the matriptase zymogen towards a peptide-based substrate as well as the natural protein substrates, pro-HGF and pro-prostasin, can be inhibited by HAI-1 and HAI-2. Inhibition of zymogen matriptase by HAI-1 and HAI-2 appears similar to inhibition of activated matriptase and occurs at comparable inhibitor concentrations. This indicates that HAI-1 and HAI-2 interact with the active sites of zymogen and activated matriptase in a similar manner. Our results suggest that HAI-1 and HAI-2 regulate matriptase zymogen activity and thus may act as regulators of matriptase trans(auto)-activation. Due to the main localisation of HAI-2 in the ER and HAI-1 in the secretory pathway and on the cell surface, this regulation likely occurs both in the secretory pathway and on the plasma membrane. Regulation of an active zymogen form of a protease is a novel finding.

Blocking the proteolytic activity of zymogen matriptase with antibody-based inhibitors.

Matriptase is a member of the type-II transmembrane serine protease (TTSP) family and plays a crucial role in the development and maintenance of epithelial tissues. As all chymotrypsin-like serine proteases, matriptase is synthesized as a zymogen (proform), requiring a cleavage event for full activity. Recent studies suggest that the zymogen of matriptase possesses enough catalytic activity to not only facilitate autoactivation, but also carry out its in vivo functions, which include activating several proteolytic and signaling cascades. Inhibition of zymogen matriptase may therefore be a highly effective approach for limiting matriptase activity. To this end, here we sought to characterize the catalytic activity of human zymogen matriptase and to develop mAb inhibitors against this enzyme form. Using a mutated variant of matriptase in which the serine protease domain is locked in the zymogen conformation, we confirmed that the zymogen form of human matriptase has catalytic activity. Moreover, the crystal structure of the catalytic domain of zymogen matriptase was solved to 2.5 Å resolution to characterize specific antibody-based matriptase inhibitors and to further structure-based studies. Finally, we describe the first antibody-based competitive inhibitors that target both the zymogen and activated forms of matriptase. We propose that these antibodies provide a more efficient way to regulate matriptase activity by targeting the protease both before and after its activation and may be of value for both research and preclinical applications.

The solution structure of the MANEC-type domain from hepatocyte growth factor activator inhibitor-1 reveals an unexpected PAN/apple domain-type fold.

A decade ago, motif at N-terminus with eight-cysteines (MANEC) was defined as a new protein domain family. This domain is found exclusively at the N-terminus of >400 multi-domain type-1 transmembrane proteins from animals. Despite the large number of MANEC-containing proteins, only one has been characterized at the protein level: hepatocyte growth factor activator inhibitor-1 (HAI-1). HAI-1 is an essential protein, as knockout mice die in utero due to placental defects. HAI-1 is an inhibitor of matriptase, hepsin and hepatocyte growth factor (HGF) activator, all serine proteases with important roles in epithelial development, cell growth and homoeostasis. Dysregulation of these proteases has been causatively implicated in pathological conditions such as skin diseases and cancer. Detailed functional understanding of HAI-1 and other MANEC-containing proteins is hampered by the lack of structural information on MANEC. Although many MANEC sequences exist, sequence-based database searches fail to predict structural homology. In the present paper, we present the NMR solution structure of the MANEC domain from HAI-1, the first three-dimensional (3D) structure from the MANEC domain family. Unexpectedly, MANEC is a new subclass of the PAN/apple domain family, with its own unifying features, such as two additional disulfide bonds, two extended loop regions and additional α-helical elements. As shown for other PAN/apple domain-containing proteins, we propose a similar active role of the MANEC domain in intramolecular and intermolecular interactions. The structure provides a tool for the further elucidation of HAI-1 function as well as a reference for the study of other MANEC-containing proteins.

Structural insight into inactivation of plasminogen activator inhibitor-1 by a small-molecule antagonist.

Plasminogen activator inhibitor-1 (PAI-1), a serpin, is the physiological inhibitor of tissue-type and urokinase-type plasminogen activators and thus also an inhibitor of fibrinolysis and tissue remodeling. It is a potential therapeutic target in many pathological conditions, including thrombosis and cancer. Several types of PAI-1 antagonist have been developed, but the structural basis for their action has remained largely unknown. Here we report X-ray crystal structure analysis of PAI-1 in complex with a small-molecule antagonist, embelin. We propose a mechanism for embelin-induced rapid conversion of PAI-1 into a substrate for its target proteases and the subsequent slow conversion of PAI-1 into an irreversibly inactivated form. Our work provides structural clues to an understanding of PAI-1 inactivation by small-molecule antagonists and an important step toward the design of drugs targeting PAI-1.