Hee-Bong Lee

TXNIP Deficiency Exacerbates Endotoxic Shock via the Induction of Excessive Nitric Oxide Synthesis

Thioredoxin-interacting protein (TXNIP) has multiple functions, including tumor suppression and involvement in cell proliferation and apoptosis. However, its role in the inflammatory process remains unclear. In this report, we demonstrate that Txnip−/− mice are significantly more susceptible to lipopolysaccharide (LPS)-induced endotoxic shock. In response to LPS, Txnip−/− macrophages produced significantly higher levels of nitric oxide (NO) and inducible nitric oxide synthase (iNOS), and an iNOS inhibitor rescued Txnip−/− mice from endotoxic shock-induced death, demonstrating that NO is a major factor in TXNIP-mediated endotoxic shock. This susceptibility phenotype of Txnip−/− mice occurred despite reduced IL-1β secretion due to increased S-nitrosylation of NLRP3 compared to wild-type controls. Taken together, these data demonstrate that TXNIP is a novel molecule that links NO synthesis and NLRP3 inflammasome activation during endotoxic shock.

A Novel Thermostable Arylesterase from the Archaeon Sulfolobus solfataricus P1: Purification, Characterization, and Expression

A novel thermostable arylesterase, a 35-kDa monomeric enzyme, was purified from the thermoacidophilic archaeon Sulfolobus solfataricus P1. The optimum temperature and pH were 94 degrees C and 7.0, respectively. The enzyme displayed remarkable thermostability: it retained 52% of its activity after 50 h of incubation at 90 degrees C. In addition, the purified enzyme showed high stability against denaturing agents, including various detergents, urea, and organic solvents. The enzyme has broad substrate specificity besides showing an arylesterase activity toward aromatic esters: it exhibits not only carboxylesterase activity toward tributyrin and p-nitrophenyl esters containing unsubstituted fatty acids from butyrate (C(4)) to palmitate (C(16)), but also paraoxonase activity toward organophosphates such as p-nitrophenylphosphate, paraoxon, and methylparaoxon. The k(cat)/K(m) ratios of the enzyme for phenyl acetate and paraoxon, the two most preferable substrates among all tested, were 30.6 and 119.4 s(-1) microM(-1), respectively. The arylesterase gene consists of 918 bp corresponding to 306 amino acid residues. The deduced amino acid sequence shares 34% identity with that of arylesterase from Acinetobacter sp. strain ADP1. Furthermore, we successfully expressed active recombinant S. solfataricus arylesterase in Escherichia coli. Together, our results show that the enzyme is a serine esterase belonging to the A-esterases and contains a catalytic triad composed of Ser156, Asp251, and His281 in the active site.

Ephedrannin A and B from roots of Ephedra sinica inhibit lipopolysaccharide-induced inflammatory mediators by suppressing nuclear factor-κB activation in RAW 264.7 macrophages.

Ephedra sinica is a traditional Chinese medicinal herb and has pharmacological functions including anti-inflammatory effects. However, the active ingredients from Ephedra roots have not been characterized. Here, two active constituents were isolated and their structures and mechanisms of action were defined. Active constituents from Ephedra roots were isolated by continuous solvent-extractions and column chromatography. Their structures were determined by use of multiple types of spectrometry. The mechanisms of action were examined using lipopolysaccharide (LPS)-stimulated RAW 264.7 cells through PCR, ELISA, electrophoretic mobility shift assays, and immunocytochemistry. Two active constituents, ephedrannin A and B, belonging to the A-type proanthocyanidin family were identified. Both ephedrannin A and B effectively suppressed the transcription of tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β). These compounds exerted their anti-inflammatory actions on LPS-stimulated macrophages by suppressing the translocation of nuclear factor-kappa B (NF-κB) and the phosphorylation of p38 mitogen-activated protein (MAP) kinase. Ephedrannin A and B both exhibited strong anti-inflammatory effects, however, the optimal dose of ephedrannin B was 10 times lower than that of ephedrannin A. This is the first report describing effective anti-inflammatory activity for ephedrannin A and B isolated from Ephedra roots. Ephedrannin B may be a good candidate for delaying the progression of human inflammatory diseases and warrants further studies.

Chaperone‐like function of lipocortin 1

Lipocortin 1 (LC1) is a 37 kDa member of the annexin family of proteins. It has been proposed to act as a mediator of some of the actions of glucocorticoids in anti‐inflammatory and immune suppressive functions. LC1 has been shown to play a role in cell proliferation, apoptosis, and differentiation. However, the exact biological functions of LC1 still remain obscure. Here it is shown that LC1 displays a chaperone‐like function. Stoichiometric amounts of LC1 suppressed thermally induced inactivation and aggregation of the test enzymes citrate synthase and glutamate dehydrogenase. LC1 was also effective in refolding guanine hydrochloride‐denatured glutamate dehydrogenase, as judged by circular dichroism spectroscopy.

A novel dienelactone hydrolase from the thermoacidophilic archaeon Sulfolobus solfataricus P1: purification, characterization, and expression.

BACKGROUNDnDienelactone hydrolases catalyze the hydrolysis of dienelactone to maleylacetate, which play a key role for the microbial degradation of chloroaromatics via chlorocatechols. Here, a thermostable dienelactone hydrolase from thermoacidophilic archaeon Sulfolobus solfataricus P1 was the first purified and characterized and then expressed in Escherichia coli.nnnMETHODSnThe enzyme was purified by using several column chromatographys and characterized by determining the enzyme activity using p-nitrophenyl caprylate and dienelactones. In addition, the amino acids related to the catalytic mechanism were examined by site-directed mutagenesis using the identified gene.nnnRESULTSnThe enzyme, approximately 29 kDa monomeric, showed the maximal activity at 74 degrees C and pH 5.0, respectively. The enzyme displayed remarkable thermostability: it retained approximately 50% of its activity after 50 h of incubation at 90 degrees C, and showed high stability against denaturing agents, including various detergents, urea, and organic solvents. The enzyme displayed substrate specificities toward trans-dienelactone, not cis-isomer, and also carboxylesterase activity toward p-nitrophenyl esters ranging from butyrate (C₄) to laurate (C₁₂). The k(cat)/K(m) ratios for trans-dienelactone and p-nitrophenyl caprylate (C₈), the best substrate, were 92.5 and 54.7 s⁻¹ μM⁻¹, respectively.nnnCONCLUSIONSnThe enzyme is a typical dienelactone hydrolase belonging to alpha/beta hydrolase family and containing a catalytic triad composed of Cys151, Asp198, and His229 in the active site.nnnGENERAL SIGNIFICANCEnThe enzyme is the first characterized archaeal dienelactone hydrolase.

Inhibitory effect of ephedrannins A and B from roots of Ephedra sinica STAPF on melanogenesis

BACKGROUNDnMelanogenesis, a process producing the pigment melanin in human skin, eyes and hair, is a major physiological response against various environmental stresses, in particular exposure to ultraviolet radiation, and its pathway is regulated by a key enzyme, tyrosinase. In this study, we evaluated the effects of ephedrannins A and B, which are polyphenols from the roots of Ephedra sinica, commonly used in herbalism in oriental countries, on mushroom tyrosinase and melanogenesis in B16F10 melanoma cells.nnnMETHODSnTheir effects on mushroom tyrosinase were determined via kinetic studies using a spectrophotometric analysis and those on melanin and tyrosinase production in melanoma cells treated with α-MSH (melanin stimulating hormone) were examined using PCR and ELISA.nnnRESULTSnBoth ephedrannins A and B exhibited concentration-dependent inhibitory effects on L-tyrosine oxidation by mushroom tyrosinase, and the inhibition mechanism was competitive and reversible with L-tyrosine as the substrate. In addition, melanin production in melanoma cells was also suppressed in a concentration-dependent manner by ephedrannins A and B without significant effects on cell proliferation at the concentrations tested. Both compounds showed inhibitory effects on melanin production by suppressing the transcription of tyrosinase in the cells.nnnCONCLUSIONnBoth compounds exhibited significant inhibitory effects, but the inhibition by ephedrannin B was much more effective than that by ephedrannin A. Both ephedrannins A and B may be good candidates for a whitening agent for skin.nnnGENERAL SIGNIFICANCEnThis is the first report that describes effective inhibition of melanin production by ephedrannins A and B isolated from Ephedra roots.

Identification of amino acids related to catalytic function of Sulfolobus solfataricus P1 carboxylesterase by site-directed mutagenesis and molecular modeling.

The archaeon Sulfolobus solfataricus P1 carboxylesterase is a thermostable enzyme with a molecular mass of 33.5 kDa belonging to the mammalian hormone-sensitive lipase (HSL) family. In our previous study, we purified the enzyme and suggested the expected amino acids related to its catalysis by chemical modification and a sequence homology search. For further validating these amino acids in this study, we modified them using site-directed mutagenesis and examined the activity of the mutant enzymes using spectrophotometric analysis and then estimated by homology modeling and fluorescence analysis. As a result, it was identified that Ser151, Asp244, and His274 consist of a catalytic triad, and Gly80, Gly81, and Ala152 compose an oxyanion hole of the enzyme. In addition, it was also determined that the cysteine residues are located near the active site or at the positions inducing any conformational changes of the enzyme by their replacement with serine residues. [BMB Reports 2016; 49(6): 349-354]