Native structure of the RhopH complex, a key determinant of malaria parasite nutrient acquisition

The RhopH complex is implicated in malaria parasites’ ability to invade and create new permeability pathways in host erythrocytes, but its mechanisms remain poorly understood. Here, we enrich the endogenous RhopH complex in a native soluble form, comprising RhopH2, CLAG3.1, and RhopH3, directly from parasite cell lysates and determine its atomic structure using cryo–electron microscopy (cryo-EM), mass spectrometry, and the cryoID program. CLAG3.1 is positioned between RhopH2 and RhopH3, which both share substantial binding interfaces with CLAG3.1 but make minimal contacts with each other. The forces stabilizing individual subunits include 13 intramolecular disulfide bonds. Notably, CLAG3.1 residues 1210 to 1223, previously predicted to constitute a transmembrane helix, are embedded within a helical bundle formed by residues 979 to 1289 near the C terminus of CLAG3.1. Buried in the core of the RhopH complex and largely shielded from solvent, insertion of this putative transmembrane helix into the erythrocyte membrane would likely require a large conformational rearrangement. Given the unusually high disulfide content of the complex, it is possible that such a rearrangement could be initiated by the breakage of allosteric disulfide bonds, potentially triggered by interactions at the erythrocyte membrane. This first direct observation of an exported Plasmodium falciparum transmembrane protein—in a soluble, trafficking state and with atomic details of buried putative membrane-insertion helices—offers insights into the assembly and trafficking of RhopH and other parasite-derived complexes to the erythrocyte membrane. Our study demonstrates the potential the endogenous structural proteomics approach holds for elucidating the molecular mechanisms of hard-to-isolate complexes in their native, functional forms.

Effect of Hair Straightening Treatment on Porosity and Cysteic Acid Content of Hair

Background: Chemical straightening has increased in popularity because of its durability over thermal straightening and because it gives the hair a natural smooth, shiny look, more styling options for a longer time. The aim of this study was to evaluate the degree of damage that occur to the hair after chemical straightener treatment by assessing the change in hair porosity and hair cysteic acid content before and after straightener treatment. Methods: Forty hair samples were collected from female volunteers; each sample was divided into 2 groups; group A (before straightening) and group B (after straightening). Hair samples were washed then blow dried after that hair straightener was applied for 30 min then flat iron was done, hair samples were washed and blow dried. Each group was subjected to test their porosity and Fourier transform infrared spectroscopy examination to assess cysteic acid content. Results: Hair porosity showed significant increase after straitening. Cysteic acid and disulfide content showed insignificant difference between both groups. Conclusion: Hair straighteners may cause great damage to hair internal structures. So, proper choice of the material used and assessing the hair characters before straightening is necessary.

Effect of alloxan on glutathione system and oxidative protein modification in adipocytes of rats at experimental diabetes

There was carried out a research of the development of oxidative stress, the condition of glutathione dependant system of antioxidant protection in adipocytes of epididymal adipose tissue of rats when injecting alloxan. The development of oxidative stress in adipocytes was characterized by the increase of lipids hydroperoxide concentration, products reacting with thiobarbituric acid, and the increase of carbonylderived protein. Redox-condition in adipocytes was considerably changing that was specified by the decrease of the content of the reduced form of glutathione and tendency to the increase of glutathione disulfide content, decrease of ratio between reduced and oxidized forms of threepeptide. Damage of protein molecule at oxidative stress may lead to the abnormality of transduction of insulinic signal and appearance of insulin resistance in adipose tissue.

A Mycothiol Synthase Mutant of Mycobacterium tuberculosis Has an Altered Thiol-Disulfide Content and Limited Tolerance to Stress

ABSTRACT Mycothiol (MSH) (acetyl-Cys-GlcN-Ins) is the major low-molecular-mass thiol in Mycobacterium tuberculosis. MSH has antioxidant activity, can detoxify a variety of toxic compounds, and helps to maintain the reducing environment of the cell. The production of MSH provides a potential novel target for tuberculosis treatment. Biosynthesis of MSH requires at least four genes. To determine which of these genes is essential in M. tuberculosis, we have been constructing targeted gene disruptions. Disruption in the mshC gene is lethal to M. tuberculosis, while disruption in the mshB gene results in MSH levels 20 to 100% of those of the wild type. For this study, we have constructed a targeted gene disruption in the mshD gene that encodes mycothiol synthase, the final enzyme in MSH biosynthesis. The mshD mutant produced ∼1% of normal MSH levels but high levels of the MshD substrate Cys-GlcN-Ins and the novel thiol N-formyl-Cys-GlcN-Ins. Although N-formyl-Cys-GlcN-Ins was maintained in a highly reduced state, Cys-GlcN-Ins was substantially oxidized. In both the wild type and the mshD mutant, cysteine was predominantly oxidized. The M. tuberculosis mshD mutant grew poorly on agar plates lacking catalase and oleic acid and in low-pH media and had heightened sensitivity to hydrogen peroxide. The inability of the mshD mutant to survive and grow in macrophages may be associated with its altered thiol-disulfide status. It appears that N-formyl-Cys-GlcN-Ins serves as a weak surrogate for MSH but is not sufficient to support normal growth of M. tuberculosis under stress conditions such as those found within the macrophage.

Responses of glutathione system and antioxidant enzymes to exhaustive exercise and hydroperoxide

Glutathione (gamma-glutamylcysteinylglycine) is one of the major antioxidants in the body. The present study investigated the changes of glutathione status, oxidative injury, and antioxidant enzyme systems after an exhaustive bout of treadmill running and/or hydroperoxide injection in male Sprague-Dawley rats. Concentrations of total and reduced glutathione in deep vastus lateralis muscle were significantly increased (P less than 0.01) after exhaustive exercise with either hydroperoxide (t-butyl hydroperoxide) or saline injection, whereas hydroperoxide alone had no significant effect. Exhaustive exercise increased muscle glutathione disulfide content by 75 and 60% (P less than 0.05), respectively, in hydroperoxide and saline groups. Concentrations of glutathione-related amino acids glutamate, cysteine, and aspartate were significantly increased in the same muscle after exhaustion. Hepatic glutathione status was not affected by either hydroperoxide injection or exercise. Glutathione peroxidase, glutathione reductase, superoxide dismutase, and catalase activities were significantly elevated after exhaustive exercise with or without hydroperoxide injection in muscle but not in liver. Hydroperoxide and exhaustive exercise enhanced lipid peroxidation in muscle and liver, respectively. It is concluded that exhaustive exercise can impose a severe oxidative stress on skeletal muscle and that glutathione systems as well as antioxidant enzymes are important in coping with free radical-mediated muscle injury.