Osteocyte- and late osteoblast-derived NOTUM reduces cortical bone mass in mice

Osteoporosis is a common skeletal disease, with increased risk of fractures. Currently available osteoporosis treatments reduce the risk of vertebral fractures, mainly dependent on trabecular bone, whereas the effect on nonvertebral fractures, mainly dependent on cortical bone, is less pronounced. WNT signaling is a crucial regulator of bone homeostasis, and the activity of WNTs is inhibited by NOTUM, a secreted WNT lipase. We previously demonstrated that conditional inactivation of NOTUM in all osteoblast lineage cells increases the cortical but not the trabecular bone mass. The aim of the present study was to determine if NOTUM increasing cortical bone is derived from osteoblast precursors/early osteoblasts or from osteocytes/late osteoblasts. First, we demonstrated Notum mRNA expression in Dmp1-expressing osteocytes and late osteoblasts in cortical bone using in situ hybridization. We then developed a mouse model with inactivation of NOTUM in Dmp1-expressing osteocytes and late osteoblasts (Dmp1-creNotum^flox/flox mice). We observed that the Dmp1-creNotum^flox/flox mice displayed a substantial reduction of Notum mRNA in cortical bone, resulting in increased cortical bone mass and decreased cortical porosity in femur but no change in trabecular bone volume fraction in femur or in the lumbar vertebrae L5 in Dmp1-creNotum^flox/flox mice as compared with control mice. In conclusion, osteocytes and late osteoblasts are the principal source of NOTUM in cortical bone, and NOTUM derived from osteocytes/late osteoblasts reduces cortical bone mass. These findings demonstrate that inhibition of osteocyte/late osteoblast-derived NOTUM might be an interesting pharmacological target to increase cortical bone mass and reduce nonvertebral fracture risk.NEW & NOTEWORTHY NOTUM produced by osteoblasts is known to regulate cortical bone mass. Our new findings show that NOTUM specifically derived by DMP1-expressing osteocytes and late osteoblasts regulates cortical bone mass and not trabecular bone mass.

Knockout of rapC Improves the Bacillomycin D Yield Based on De Novo Genome Sequencing of Bacillus amyloliquefaciens fmbJ

Bacillus amyloliquefaciens, a Gram-positive and soil-dwelling bacterium, could produce secondary metabolites that suppress plant pathogens. In this study, we provided the whole genome sequence results of B. amyloliquefaciens fmbJ, which had one circular chromosome of 4 193 344 bp with 4249 genes, 87 tRNA genes, and 27 rRNA genes. In addition, fmbJ was found to contain several gene clusters of antimicrobial lipopeptides (bacillomycin D, surfactin, and fengycin), and bacillomycin D homologues were further comprehensively identified. To clarify the influence of rapC regulating the synthesis of lipopeptide on the yield of bacillomycin D, rapC gene in fmbJ was successfully deleted by the marker-free method. Finally, it was found that the deletion of rapC gene in fmbJ significantly improved bacillomycin D production from 240.7 ± 18.9 to 360.8 ± 30.7 mg/L, attributed to the increased the expression of bacillomycin D synthesis-related genes through enhancing the transcriptional level of comA, comP, and phrC. These results showed that the production of bacillomycin D in B. amyloliquefaciens fmbJ might be regulated by the RapC-PhrC system. The findings are expected to advance further agricultural application of Bacillus spp. as a promising source of natural bioactive compounds.

Esterases of Varroa destructor (Acari: Varroidae), parasitic mite of the honeybee

Varroa destructor is an ectoparasite that causes serious damage to the population of the honeybee. Increasing resistance of the parasite to acaricides is related, among others, to metabolic adaptations of its esterases to facilitate decomposition of the chemicals used. Esterases are a large heterogeneous group of enzymes that metabolize a number of endogenous and exogenous substrates with ester binding. The aim of the present study was to determine the activity of esterases in the body extracts (BE) and excretion/secretion products (E/SP) of the mite. The enzymes contained in the E/SP should originate mainly from the salivary glands and the alimentary system and they may play a particularly important role in the first line of defence of the mite against acaricides. Activity of cholinesterases (ChEs) [acetylcholinesterase (AChE) and butyrylcholinesterase], carboxylesterases (CEs) and phosphatases [alkaline phosphatase (AP) and acid phosphatase (AcP)] was investigated. The activity of all the enzymes except AChE was higher in the E/SP than in the BE. ChEs from the BE and from the E/SP reacted differently on eserine, a ChE inhibitor. Eserine inhibited both enzymes from the BE, increased decomposition of acetylcholine, but did not influence hydrolysis of butyrylcholine by the E/SP. Activity of the CEs from the BE in relation to the esters of carboxylic acids can be presented in the following series: C10 > C12 > C14 > C8 > C2 > C4 = C16, while activity of the CEs from the E/SP was: C4 > C8 > C2 > C14 > C10 > C12 > C16. The inhibitor of CEs, triphenyl phosphate, reduced the activity of esterases C2–C8 and C14–C16; however, it acted in the opposite way to CEs C10 and C12. The activity of both phosphatases was higher in the E/SP than in the BE (AcP about twofold and AP about 2.6-fold); the activities of AP and AcP in the same material were similar. Given the role of esterases in resistance to pesticides, further studies are necessary to obtain complete biochemical characteristics of the enzymes currently present in V. destructor.

[Partial characterization of esterase activity in a temephos-resistant Aedes aegypti strain]

INTRODUCTION

the esterase enzymes have been defined as the mechanism of resistance to temephos in Aeges aegypti in Cuba, which is the most used larvacide worldwide.

OBJECTIVE

to partially characterize the activity of esterases in exposed and nonexposed larvae at sublethal doses of temephos in an Aedes aegypti strain that is resistant to this product.

METHODS

a susceptible reference Aedes aegypti strain (Rockefeller) and another temephos-resistant strain (SANtemFII) were used. The larvae from SANtemF11 strain were exposed to lethal concentration 90 (LC90) of temephos (1 ppm); 10 % of the surviving larvae after 24 hours (SANtem[24 h] was moved to clean water, with no exposure to insecticide for 24 hours (SANtem [48 h]). The activity of esterases was partially characterized in these larvae through biochemical assays and gel-polyacrylamide electrophoresis. The molecular weight of esterase A 4 (ESt. A4) was estimated with the support of sodium duodecyl sulophate (SDS-PAGE).

RESULTS

the activity of esterases in SANtemF11 was significantly higher than in Rockefeller strain. Significant reduction of the activity of esterases in surviving larvae was observed (SANtemF11 [24 h], but it increased 24 h later without exposure to temephos. The zymogram showed that 10% of larvae that survived from temephos action, just the esterase A4 band increased if compared with those of SAntemF11. The estimated molecular weight of esterase A4 was 58 kDa.

CONCLUSIONS

the presence of a specific band of esterase (58 kDa) in surviving larvae confirmed the role of these enzymes in insecticidal resistance. The diagnosis of the function of the esterases in resistance to temephos through biochemical tests should not be made in larvae exposed to sublethal doses of this insecticide, in order to avoid false negatives.

Structural and functional profile of the carbohydrate esterase gene complement in Phytophthora infestans

The plant cell cuticle is the first obstacle for penetration of the host by plant pathogens. To breach this barrier, most pathogenic fungi employ a complex assortment of cell wall-degrading enzymes including carbohydrate esterases, glycoside hydrolases, and polysaccharide lyases. We characterized the full complement of carbohydrate esterase-coding genes in three Phytophthora species and analyzed the expression of cutinase in vitro and in planta; we also determined the cutinase allele distribution in multiple isolates of P. infestans. Our investigations revealed that there are 49, 21, and 37 esterase homologs in the P. infestans, P. ramorum, and P. sojae genomes, respectively, with a considerable number predicted to be extracellular. Four cutinase gene copies were found in both the P. infestans and P. ramorum genomes, while 16 copies were found in P. sojae. Transcriptional analyses of cutinase in P. infestans revealed that its expression level during infection is significantly upregulated at all time points compared to that of the same gene in mycelium grown in vitro. Expression achieves maximum values at 15 hpi, declining at subsequent time points. These results may suggest, therefore, that cutinase most likely plays a role in P. infestans pathogenicity.

Mechanistic plasticity of sexual reproduction and meiosis in the Candida pathogenic species complex

BACKGROUND

Candida species are microbial pathogens originally thought to be asexual, but several are now recognized as sexual or parasexual. Candida albicans, the most common fungus infecting humans, is an obligate diploid with a parasexual cycle involving mating, recombination, and genome reduction but no recognized meiosis. Others (C. lusitaniae, C. guilliermondii) are haploid, and their mating produces spores, suggestive of complete meiotic sexual cycles. However, comparative genomic analysis reveals that these species lack key meiotic components, including the recombinase Dmc1 and cofactors (Mei5/Sae3), synaptonemal-complex proteins (Zip1-Zip4/Hop1), and the crossover interference pathway (Msh4/5).

RESULTS

Here we elucidate the structure and functions of the mating-type (MAT) locus and establish that C. lusitaniae undergoes meiosis during its sexual cycle. The MAT-encoded a2 (high-mobility group) and alpha1 (alpha domain) factors specify a and alpha cell identity, whereas the a1 homeodomain protein drives meiosis and sporulation and functions without its canonical heterodimeric partner, alpha2. Despite the apparent loss of meiotic genes, C. lusitaniae undergoes meiosis during sexual reproduction involving diploid intermediates, frequent SPO11-dependent recombination, and whole-genome reduction generating haploid progeny. The majority of meiotic progeny are euploid, but approximately one-third are diploid/aneuploid.

CONCLUSIONS

The cell identity and meiotic pathways have been substantially rewired, and meiotic generation of both recombinant and aneuploid progeny may expand genetic diversity. These findings inform our understanding of sexual reproduction in pathogenic microbes and the evolutionary plasticity of the meiotic machinery, with implications for the sexual nature of C. albicans and the generation and consequences of aneuploidy in biology and medicine.

A cell wall-degrading esterase of Xanthomonas oryzae requires a unique substrate recognition module for pathogenesis on rice

Xanthomonas oryzae pv oryzae (Xoo) causes bacterial blight, a serious disease of rice (Oryza sativa). LipA is a secretory virulence factor of Xoo, implicated in degradation of rice cell walls and the concomitant elicitation of innate immune responses, such as callose deposition and programmed cell death. Here, we present the high-resolution structural characterization of LipA that reveals an all-helical ligand binding module as a distinct functional attachment to the canonical hydrolase catalytic domain. We demonstrate that the enzyme binds to a glycoside ligand through a rigid pocket comprising distinct carbohydrate-specific and acyl chain recognition sites where the catalytic triad is situated 15 A from the anchored carbohydrate. Point mutations disrupting the carbohydrate anchor site or blocking the pocket, even at a considerable distance from the enzyme active site, can abrogate in planta LipA function, exemplified by loss of both virulence and the ability to elicit host defense responses. A high conservation of the module across genus Xanthomonas emphasizes the significance of this unique plant cell wall-degrading function for this important group of plant pathogenic bacteria. A comparison with the related structural families illustrates how a typical lipase is recruited to act on plant cell walls to promote virulence, thus providing a remarkable example of the emergence of novel functions around existing scaffolds for increased proficiency of pathogenesis during pathogen-plant coevolution.

ABHD5/CGI-58 facilitates the assembly and secretion of apolipoprotein B lipoproteins by McA RH7777 rat hepatoma cells

Lipolysis of stored triacylglycerols provides lipid precursors for the assembly of apolipoprotein B (apoB) lipoproteins in hepatocytes. Abhydrolase domain containing 5 (ABHD5) is expressed in liver and facilitates the lipolysis of triacylglycerols. To study the function of ABHD5 in lipoprotein secretion, we silenced the expression of ABHD5 in McA RH7777 cells using RNA interference and studied the metabolism of lipids and secretion of apoB lipoproteins. McA RH7777 cells deficient in ABHD5 secreted reduced amounts of apoB, triacylglycerols, and cholesterol esters. Detailed analysis of liquid chromatography-mass spectrometry data for the molecular species of secreted triacylglycerols revealed that deficiency of ABHD5 significantly reduced secretion of triacylglycerols containing oleate, even when oleate was supplied in the culture medium; the ABHD5-deficient cells partially compensated by secreting higher levels of triacylglycerols containing saturated fatty acids. In experiments tracking the metabolism of [(14)C]oleate, silencing of ABHD5 reduced lipolysis of cellular triacylglycerols and incorporation of intermediates derived from stored lipids into secreted triacylglycerols and cholesterol esters. In contrast, the incorporation of exogenous oleate into secreted triacylglycerols and cholesterol esters was unaffected by deficiency of ABHD5. These findings suggest that ABHD5 facilitates the use of lipid intermediates derived from lipolysis of stored triacylglycerols for the assembly of lipoproteins.

Characterization of novel esterases in insecticide-resistant mosquitoes

In the mosquito Culex pipiens complex (Diptera: Culicidae), the amplification of carboxylesterase genes is an important mechanism providing resistance to organophosphate insecticides. Various amplified alleles at the Ester locus have been identified over the world. In this study, two newly detected Ester alleles, Ester(B10) and Ester(11) (including associated Ester(A11) and Ester(B11)), coding for esterases B10 and A11-B11, respectively, are characterized qualitatively and quantitatively. A high molecular identity is observed both at the nucleotide level and at the deduced amino acid level among the known Ester alleles. Real-time quantitative PCR results suggest 2.5-fold amplification of the Ester(B10) allele, 36.5-fold amplification of the Ester(A11) allele, and 19.1-fold amplification of the Ester(B11) allele. The ca. 2-fold difference in amplification level between Ester(A11) and Ester(B11) may indicate a new model for the esterase amplification. Bioassays show that these two resistant Ester alleles only can confer moderate or low resistance to the tested organophosphate insecticides.

Regulating double-stranded DNA break repair towards crossover or non-crossover during mammalian meiosis

During meiosis the programmed induction of DNA double-stranded breaks (DSB) leads to crossover (CO) and non-crossover products (NCO). One key role of CO is to connect homologs before metaphase I and thus to ensure the proper reductional segregation. This role implies an accurate regulation of CO frequency with the establishment of at least one CO per chromosome arm. Current major challenges are to understand how CO and NCO formation are regulated and what is the role of NCO. We present here the current knowledge about CO and NCO and their regulation in mammals. CO density varies widely along chromosomes and their distribution is not random as they are subject to positive interference. As documented in the mouse and human, a significant excess of DSB are generated relative to the number of CO. In fact, evidence has been obtained for the formation of NCO products, for regulation of the choice of DSB repair towards CO or NCO and for a CO specific pathway. We discuss the roles of Msh4, Msh5 and Sycp1 which affect DSB repair and probably not only the CO pathway. We suggest that, in mammals, the regulation of NCO differs from that described in Saccharomyces cerevisiae.

CGI-58 facilitates the mobilization of cytoplasmic triglyceride for lipoprotein secretion in hepatoma cells

Comparative Gene Identification-58 (CGI-58) is a member of the alpha/beta-hydrolase family of proteins. Mutations in the human CGI-58 gene are associated with Chanarin-Dorfman syndrome, a rare autosomal recessive genetic disease in which excessive triglyceride (TG) accumulation occurs in multiple tissues. In this study, we investigated the role of CGI-58 in cellular lipid metabolism in several cell models and discovered a role for CGI-58 in promoting the packaging of cytoplasmic TG into secreted lipoprotein particles in hepatoma cells. Using both gain-of-function and loss-of-function approaches, we demonstrate that CGI-58 facilitates the depletion of cellular TG stores without altering cellular cholesterol or phospholipid accumulation. This depletion of cellular TG is attributable solely to augmented hydrolysis, whereas TG synthesis was not affected by CGI-58. Furthermore, CGI-58-mediated TG hydrolysis can be completely inhibited by the known lipase inhibitors diethylumbelliferyl phosphate and diethyl-p-nitrophenyl phosphate, but not by p-chloro-mercuribenzoate. Intriguingly, CGI-58-driven TG hydrolysis was coupled to increases in both fatty acid oxidation and secretion of TG. Collectively, this study reveals a role for CGI-58 in coupling lipolytic degradation of cytoplasmic TG to oxidation and packaging into TG-rich lipoproteins for secretion in hepatoma cells.

[Determination in vivo of the role of esterase and glutathione transferase enzymes in pyrethroid resistance of Aedes aegypti (Diptera: Culicidae)]

An in vivo study of two synergists, that is, Triphenil phosphate -specific esterase inhibitor- and ethacrynic acid -specific gluthation transferase inhibitor- was performed to determine if these enzymes were responsible for pyrethroid resistance of Aedes aegypti. To this end, two insecticide resistant Aedes aegypti strains were used, one strain selected with temephos by six selection generations (SAN-F6) and the other strain with delmamethrin by 12 selection generations (SAN-F12), being both strains resistant to pyrethroid insecticices. Through the use of TPP and EA synergists, it was proved that esterase and gluthation-s-transferase (GST) enzymes were responsible for pryrethroid resistance of these strains. These results showed the existence of cross-resistance and multidrug resistance, which should be taken into account for insecticide use strategies aimed at vector control.

[Insecticide resistance mechanisms of Aedes aegypti (Diptera: Culicidae) from two Peruvian provinces]

Insecticide resistance of Aedes aegypti larvae and adults from two Peruvian provinces, that is, Trujillo and Tumbes provinces, was conducted. High infestation indexes and extensive use of insecticides based on the Vector Surveillance and Control Strategy of the Ministry of Public Health prevailed in these places. Larval bioassays revealed susceptibility to organophosphorate insecticide called malathion in TRUJILLO strain, it being moderate to fention and fenitrotion and high to chlorpyriphos and temephos;however, TUMBES strain was susceptible to the evaluated organophosphorate compounds, except for fention, with moderate resistance. In the adult state, at the recommended dose, TRUJILLO strain showed resistence to DDT organochlorate insecticide and to pyrethoids called lambdacyalotrine and cyflutrine whereas TUMBES was resistant to DDT and to all assessed pyrethoids. None of them was resistant to chlorpiriphos in adult stage. By using synergists, the results showed that esterases and monooxigenases played an important role in the detected resistence to organophosphorate in Aedes larvae from TRUJILLO province. Biochemical assays yielded that increased activity of esterases was very frequent in TRUJILLO strain as was the case of glutathion transferase(GST) and modified acetylcholinesterase (AchR). On the other hand, the polyacrylamide gel electrophoresis allowed observing the prevalence of amplified activity of esterases A4 in TRUJILLO strain but not in TUMBES strain.

[Determination of insecticide-resistance and resistance mechanisms of Blattella germanica (Dictyoptera: Blattellidae)]

In this paper, the level of resistance to four insecticides of 3 Blatella germanica strains collected from various places in the City of Havana province was evaluated. These strains were resistant to two pyrethroids (cypermethrin and lambda-cyalothrine) and to organophosphorate malathion but susceptible to carbamate propoxur. The values of alpha and beta esterases, acetylcholinesterase and gluthatione-S-transferase were estimated in three strains involved in the study. The results of the study showed high esterase activity in all the strains, mainly beta esterases and two of the three strains presented with high gluthation-S-transferase enzyme. No changes in acetylcholinesterase were demonstrated in relation to the reference strain. The association of levels of resistance to insecticides, the possible resistance mechanisms in each strain and the results of the enzymatic activity were also analyzed.

Stable and continuous long-term enzymatic reaction using an enzyme–nanofiber composite

This study shows the preparation and application of enzyme-nanofiber composites for long-term stable operation. The enzyme-nanofiber composite was prepared by coating an enzyme aggregate, the esterase from Rhizopus oryzae, on the surface of the nanofibers. After immobilization on the nanofiber, the apparent K ( m ) for the immobilized esterase was 1.48-fold higher than that of the free esterase, with values of 0.98 and 1.35 mM for the free and immobilized enzymes, respectively. It was found that enzyme-nanofiber was very stable, even when the fibers were shaken in glass vials, preserving 80% of the initial activity for 100 days. In addition, the enzyme-nanofiber composite was used repeatedly in 30 cycles of substrate hydrolysis and still remained active. Consequently, the esterase-nanofiber composite was employed within a continuous reactor system to evaluate its use in a long-term and stable continuous substrate hydrolysis reaction. It was found that the production of p-nitrophenol was stable for at least 400 h. This study demonstrates that the enzyme-nanofiber composite can be used in both repeated-batch mode and a continuous mode for a long-term stable operation.

Decreased obesity and atherosclerosis in human paraoxonase 3 transgenic mice

Paraoxonase 3 (PON3) is a member of the PON family, which includes PON1, PON2, and PON3. Recently, PON3 was shown to prevent the oxidation of low-density lipoprotein in vitro. To test the role of PON3 in atherosclerosis and related traits, 2 independent lines of human PON3 transgenic (Tg) mice on the C57BL/6J (B6) background were constructed. Human PON3 mRNA was detected in various tissues, including liver, lung, kidney, brain, adipose, and aorta, of both lines of Tg mice. The human PON3 mRNA levels in the livers of PON3 Tg mice were 4- to 7-fold higher as compared with the endogenous mouse Pon3 mRNA levels. Human PON3 protein and activity were detected in the livers of Tg mice as well. No significant differences in plasma total, high-density lipoprotein, and very-low-density lipoprotein/low-density lipoprotein cholesterol and triglyceride and glucose levels were observed between the PON3 Tg and non-Tg mice. Interestingly, atherosclerotic lesion areas were significantly smaller in both lines of male PON3 Tg mice as compared with the male non-Tg littermates on B6 background fed an atherogenic diet. When bred onto the low-density lipoprotein receptor knockout mouse background, the male PON3 Tg mice also exhibited decreased atherosclerotic lesion areas and decreased expression of monocyte chemoattractant protein-1 in the aorta as compared with the male non-Tg littermates. In addition, decreased adiposity and lower circulating leptin levels were observed in both lines of male PON3 Tg mice as compared with the male non-Tg mice. In an F2 cross, adipose Pon3 mRNA levels inversely correlated with adiposity and related traits. Our study demonstrates that elevated PON3 expression significantly decreases atherosclerotic lesion formation and adiposity in male mice. PON3 may play an important role in protection against obesity and atherosclerosis.

Highly enantioselective kinetic resolution of two tertiary alcohols using mutants of an esterase from Bacillus subtilis

Enzyme-catalyzed kinetic resolutions of secondary alcohols are a standard procedure today and several lipases and esterases have been described to show high activity and enantioselectivity. In contrast, tertiary alcohols and their esters are accepted only by a few biocatalysts. Only lipases and esterases with a conserved GGG(A)X-motif are active, but show low activity combined with low enantioselectivity in the hydrolysis of tertiary alcohol esters. We show in this work that the problematic autohydrolysis of certain compounds can be overcome by medium and substrate engineering. Thus, 3-phenylbut-1-yn-3-yl acetate was hydrolyzed by the esterase from Bacillus subtilis (BS2, mutant Gly105Ala) with an enantioselectivity of E = 56 in the presence of 20% (v/v) DMSO compared to E = 28 without a cosolvent. Molecular modeling was used to study the interactions between BS2 and tertiary alcohol esters in their transition state in the active site of the enzyme. Guided by molecular modeling, enzyme variants with highly increased enantioselectivity were created. For example, a Glu188Asp mutant converted the trifluoromethyl analog of 3-phenylbut-1-yn-3-yl acetate with an excellent enantioselectivity (E > 100) yielding the (S)-alcohol with > 99%ee. In summary, protein engineering combined with medium and substrate engineering afforded tertiary alcohols of very high enantiomeric purity.

Comparative analysis of Phytophthora genes encoding secreted proteins reveals conserved synteny and lineage-specific gene duplications and deletions

Comparative analysis of two Phytophthora genomes revealed overall colinearity in four genomic regions consisting of a 1.5-Mb sequence of Phytophthora sojae and a 0.9-Mb sequence of P. ramorum. In these regions with conserved synteny, the gene order is largely similar; however, genome rearrangements also have occurred. Deletions and duplications often were found in association with genes encoding secreted proteins, including effectors that are important for interaction with host plants. Among secreted protein genes, different evolutionary patterns were found. Elicitin genes that code for a complex family of highly conserved Phytophthora-specific elicitors show conservation in gene number and order, and often are clustered. In contrast, the race-specific elicitor gene Avrlb-1 appeared to be missing from the region with conserved synteny, as were its five homologs that are scattered over the four genomic regions. Some gene families encoding secreted proteins were found to be expanded in one species compared with the other. This could be the result of either repeated gene duplications in one species or specific deletions in the other. These different evolutionary patterns may shed light on the functions of these secreted proteins in the biology and pathology of the two Phytophthora spp.

Adipose triglyceride lipase and hormone-sensitive lipase are the major enzymes in adipose tissue triacylglycerol catabolism

The mobilization of free fatty acids from adipose triacylglycerol (TG) stores requires the activities of triacylglycerol lipases. In this study, we demonstrate that adipose triglyceride lipase (ATGL) and hormone-sensitive lipase (HSL) are the major enzymes contributing to TG breakdown in in vitro assays and in organ cultures of murine white adipose tissue (WAT). To differentiate between ATGL- and HSL-specific activities in cytosolic preparations of WAT and to determine the relative contribution of these TG hydrolases to the lipolytic catabolism of fat, mutant mouse models lacking ATGL or HSL and a mono-specific, small molecule inhibitor for HSL (76-0079) were used. We show that 76-0079 had no effect on TG catabolism in HSL-deficient WAT but, in contrast, essentially abolished free fatty acid mobilization in ATGL-deficient fat. CGI-58, a recently identified coactivator of ATGL, stimulates TG hydrolase activity in wild-type and HSL-deficient WAT but not in ATGL-deficient WAT, suggesting that ATGL is the sole target for CGI-58-mediated activation of adipose lipolysis. Together, ATGL and HSL are responsible for more than 95% of the TG hydrolase activity present in murine WAT. Additional known or unknown lipases appear to play only a quantitatively minor role in fat cell lipolysis.

Prenylcysteine methylesterase in Arabidopsis thaliana

Prenylated proteins undergo a series of post-translational modifications, including prenylation, proteolysis, and methylation. Collectively, these modifications generate a prenylcysteine methylester at the carboxyl terminus and modulate protein targeting and function. Prenylcysteine methylation is the only reversible step in this series of modifications. However, prenylcysteine alpha-carboxyl methylesterase (PCME) activity has not been described in plants. We have detected a specific PCME activity in Arabidopsis thaliana membranes that discriminates between biologically relevant and irrelevant prenylcysteine methylester substrates. Furthermore, we have identified an Arabidopsis gene (At5g15860) that encodes measurable PCME activity in recombinant yeast cells with greater specificity for biologically relevant prenylcysteine methylesters than the activity found in Arabidopsis membranes. These results suggest that specific and non-specific esterases catalyze the demethylation of prenylcysteine methylesters in Arabidopsis membranes. Our findings are discussed in the context of prenylcysteine methylation/demethylation as a potential regulatory mechanism for membrane association and function of prenylated proteins in Arabidopsis.

Effect of human serum albumin on drug metabolism: structural evidence of esterase activity of human serum albumin

Human serum albumin (HSA) is the most abundant plasma protein in the human body with a plasma concentration of 0.6mM. HSA plays an important role in drug transport and metabolism. Enzymatic activity of HSA on different substrates or drugs has been studied and documented. The structural mechanism of this activity, however, is unknown. In this study, we have determined the crystal structures of HSA-myristate in a complex of aspirin and of salicylic acid, respectively. The crystal structure of HSA-myristate-aspirin illustrates that aspirin transfers acetyl group to Lys199 and is hydrolyzed into salicylic acid by HSA. The hydrolysis product, salicylic acid, remains bound to HSA at a similar location, but it shows a very different orientation when compared with the salicylic acid in the HSA-myristate-salicylic acid ternary complex. These results not only provide the structural evidence of esterase activity of HSA, and demonstrate the conformational plasticity of HSA on drug binding, but also may provide structural information for the modulation of HSA-drug interaction by computational approach based on HSA-drug structure.

Topical Delivery of Retinyl Ascorbate Co-Drug

Chemical and enzymatic hydrolysis of the co-drug of retinoic acid (vitamin A) and ascorbic acid (vitamin C) - retinyl ascorbate (RA-AsA)--have been studied. Firstly, the amount of protein and ester hydrolysis activity was determined in crude cellular extracts from freshly excised porcine ear skin (<3 h) and stored porcine ear skin (frozen >6 months) using ethyl butyrate as model substrate. The stability of RA-AsA was then determined in the crude cell extracts with and without additional antioxidants. Lastly, the enzymatic hydrolysis of RA-AsA and retinyl-2-carboxy-2-hydroxy-ethanoate were determined by incubating with porcine liver esterase - retinol palmitate and ascorbyl palmitate were included for comparison. Freshly excised skin contained higher amounts of active proteins than previously frozen skin. RA-AsA underwent hydrolytic reduction causing the AsA moiety to disintegrate due to the presence of free radicals in the media. An intermediate was produced that seemed to be cleaved by enzymes. Addition of ascorbic acid, as antioxidant, to the media of crude protein extracts decelerated the hydrolysis rate. This was supported when RA-AsA and retinyl-2-carboxy-2-hydroxy-ethanoate were incubated separately with pure esterase. There was approximately 5-fold more soluble protein per ml of cytosol in the fresh skin compared to the stored skin. Therefore, the amount of protein present within approximately 1.5 cm(2) of skin (average diffusion area in the Franz cells used in our skin penetration studies) was 0.06 mg cm(-2) and 0.01 mg cm(-2) for fresh and stored extracts, respectively.

Role of kdr and esterase-mediated metabolism in pyrethroid-resistant populations of Haematobia irritans irritans (Diptera: Muscidae) in Brazil

The horn fly, Haematobia irritans irritans (L.) (Diptera: Muscidae), has become a problem for Brazilian cattle producers even though its introduction into Brazil is relatively recent. Failure to control this cattle pest is becoming a concern, and horn fly populations from several ranches from the state of Mato Grosso do Sul were surveyed for pyrethroid resistance. Susceptibility bioassays revealed that cypermethrin resistance was widespread and reached high levels in horn fly populations throughout the state, with resistance factors (RFs) ranging from 50.4 to 704.8. Synergist bioassays failed to detect a major role for esterases as a pyrethroid resistance mechanism in these populations, except for the highly pyrethroid-resistant Estrela do Oeste population (RF = 704.8). The kdr sodium channel gene mutation was not detected in eight of the 13 populations, but < 7% of individuals from four populations and 50% of the flies from Estrela do Oeste exhibited this mutation. Neither the superkdr sodium channel gene mutation nor a resistance-associated gene mutation in the HialphaE7 carboxylesterase were found in any of the fly populations. Although target site insensitivity (kdr) and esterase-mediated metabolism occur in horn fly populations from Mato Grosso do Sul state, it seems that they are not the major mechanism causing pyrethroid resistance in most of these populations.

[Adaptation of methods for quantification of the effect of esterase, acetylcholinesterase and glutathione-S-transferase in Blattella germanica (Dictyoptera: Blattellidae)]

The resistance mechanisms of Blatella germanica, one of the most important urban plagues worldwide since it is a mechanical vector that houses a number of highly harmful viruses, fungi, helmints and bacteria were studied. There are different control methods used against Blattella germnanica, with insecticides playing the leading role. Their uncontrolled application has caused the development of insecticice resistance in this species. This paper adapted biochemical methods to detect the enzymes esterase, acetylcholinesterase and glutathine-S-transferase as posible resistance mechanisms. To this end, all the parameters that allow finding out if a strain is susceptible or resistant to each mechanism were set.

[Mode of inheritance of temephos (Abate) resistance in Aedes aegypti (Diptera: Culicidae) from Cuba]

A study on the mode of inheritance of temephos resistance was conducted using a temephos resistant Aedes aegypti reference strain (SAN-F6) with a value of resistance factor of 200x, compared with the insecticide susceptible Aedes aegypti strain (ROCKEFELLER). Genetic crossings were performed between temephos resistant and susceptible strains. An F1 crossing was attained. The females of this F1 crossing were crossed with males from the ROCKEFELLER strain (retrocrossing), and it was found that the temephos resistance was inherited in a semidominant way and as a monofactorial trait. The activity of Est-A4 observed in the polyacrylamide gel electrophoresis and measured by biochemical assays was higher in the strain resistant to temephos (SAN-F6), lower in the susceptible strain (ROCKEFELLER), and intermediate in the crossing of these two strains. A lower effect of the resistant parental strain was observed in the retrocrossing, both in the mortality with temephos and in the activity of Est. A4. These results suggest that the esterase activity may also be inherited, as well as the resistance to temephos, as a semidominant character.

Validation of RNAi silencing specificity using synthetic genes: salicylic acid-binding protein 2 is required for innate immunity in plants

RNA interference (RNAi) is widely used to specifically silence the expression of any gene to study its function and to identify and validate therapeutic targets. Despite the popularity of this technology, recent studies have shown that RNAi may also silence non-targeted genes. Here we demonstrate the utility of a quick, efficient and robust approach to directly validate the specificity of RNAi as an alternative to indirect validation of RNAi through gene expression profiling. Our approach involves reversing (complementing) the RNAi-induced phenotype by introducing a synthetic version of the target gene that is designed to escape silencing. This synthetic gene complementation approach can also be used for mutational analysis of the target gene, or to provide a functional version of a defective protein after silencing the defective gene by RNAi. Using this approach we demonstrate that the loss of systemic acquired resistance, a form of innate immunity in plants, is indeed due to the silencing of salicylic acid-binding protein 2 rather than to off-target effects.

In vitro metabolism of MK-0767 [(+/-)-5-[(2,4-dioxothiazolidin-5-yl)methyl]-2-methoxy-N-[[(4-trifluoromethyl) phenyl]methyl]benzamide], a peroxisome proliferator-activated receptor alpha/gamma agonist. I. Role of cytochrome P450, methyltransferases, flavin monooxygenases, and esterases

The metabolism of MK-0767, (+/-)-5-[(2,4-dioxothiazolidin-5-yl)methyl]-2-methoxy-N-[[(4-trifluoromethyl) phenyl]methyl]benzamide, a thiazolidinedione (TZD)-containing peroxisome proliferator-activated receptor alpha/gamma agonist, was studied in liver microsomes and hepatocytes from humans and rat, dog, and rhesus monkey, to characterize the enzyme(s) involved in its metabolism. The major site of metabolism is the TZD ring, which underwent opening catalyzed by CYP3A4 to give the mercapto derivative, M22. Other metabolites formed in NADPH-fortified liver microsomes included the TZD-5-OH derivative (M24), also catalyzed by CYP3A4, and the O-desmethyl derivative (M28), whose formation was catalyzed by CYP2C9 and CYP2C19. Metabolite profiles from hepatocyte incubations were different from those generated with NADPH-fortified microsomal incubations. In addition to M22, M24, and M28, hepatocytes generated several S-methylated metabolites, including the methyl mercapto (M25), the methyl sulfoxide amide (M16), and the methyl sulfone amide (M20) metabolites. Addition of the methyl donor, S-adenosyl methionine, in addition to NADPH, to microsomal incubations enhanced the turnover and resulted in metabolite profiles similar to those in hepatocyte incubations. Collectively, these results indicated that methyltransferases played a major role in the metabolism of MK-0767. Using enzyme-specific inhibitors, it was concluded that microsomal thiol methyltransferases play a more important role than the cytosolic thiopurine methyltransferase. Baculovirus-expressed human flavin-containing monooxygenase 3, as well as CYP3A4, oxidized M25 to M16, whereas further oxidation of M16 to M20 was catalyzed mainly by CYP3A4. Esterases were involved in the formation of the methyl sulfone carboxylic acids, minor metabolites detected in hepatocytes.

Human paraoxonases (PON1, PON2, and PON3) are lactonases with overlapping and distinct substrate specificities

The paraoxonase (PON) gene family in humans has three members, PON1, PON2, and PON3. Their physiological role(s) and natural substrates are uncertain. We developed a baculovirus-mediated expression system, suitable for all three human PONs, and optimized procedures for their purification. The recombinant PONs are glycosylated with high-mannose-type sugars, which are important for protein stability but are not essential for their enzymatic activities. Enzymatic characterization of the purified PONs has revealed them to be lactonases/lactonizing enzymes, with some overlapping substrates (e.g., aromatic lactones), but also to have distinctive substrate specificities. All three PONs metabolized very efficiently 5-hydroxy-eicosatetraenoic acid 1,5-lactone and 4-hydroxy-docosahexaenoic acid, which are products of both enzymatic and nonenzymatic oxidation of arachidonic acid and docosahexaenoic acid, respectively, and may represent the PONs' endogenous substrates. Organophosphates are hydrolyzed almost exclusively by PON1, whereas bulky drug substrates such as lovastatin and spironolactone are hydrolyzed only by PON3. Of special interest is the ability of the human PONs, especially PON2, to hydrolyze and thereby inactivate N-acyl-homoserine lactones, which are quorum-sensing signals of pathogenic bacteria. None of the recombinant PONs protected low density lipoprotein against copper-induced oxidation in vitro.

Distinct DNA-damage-dependent and -independent responses drive the loss of oocytes in recombination-defective mouse mutants

Defects in meiotic recombination in many organisms result in arrest because of activation of a meiotic checkpoint(s). The proximal defect that triggers this checkpoint in mammalian germ cells is not understood, but it has been suggested to involve either the presence of DNA damage in the form of unrepaired recombination intermediates or defects in homologous chromosome pairing and synapsis independent of DNA damage per se. To distinguish between these possibilities in the female germ line, we compared mouse oocyte development in a mutant that fails to form the double-strand breaks (DSBs) that initiate meiotic recombination (Spo11-/-) to mutants with defects in processing DSBs when they are formed (Dmc1-/- and Msh5-/-), and we examined the epistasis relationships between these mutations. Absence of DSB formation caused a partial defect in follicle formation, whereas defects in DSB repair caused earlier and more severe meiotic arrest, which could be suppressed by eliminating DSB formation. Therefore, our analysis reveals that there are both DNA-damage-dependent and -independent responses to recombination errors in mammalian oocytes. By using these findings as a paradigm, we also examined oocyte loss in mutants lacking the DNA-damage checkpoint kinase ATM. The absence of ATM caused defects in folliculogenesis that were similar to those in Dmc1 mutants and that could be suppressed by Spo11 mutation, implying that oocyte death in Atm-deficient animals is a response to defective DSB repair.

[SPO11: an activity that promotes DNA breaks required for meiosis]

Recombination between homologous chromosomes during meiosis is an essential process, which mechanistical function is to ensure the reductional segregation of chromosomes at the first meiotic division. SPO11, one of the key genes directly involved in this process, has been at the origin of considerable interest for the past five years, for several reasons. First, Spo11 is responsible for the initiation of meiotic recombination through the formation of DNA double-strand breaks by a type II DNA topoisomerase-like activity. Moreover, Spo11, and its function, have been conserved through evolution, from yeasts to human, as demonstrated by the identification of members of the Spo11 protein family and the analyses of corresponding mutants. Indeed, for every eukaryote that has been tested, spo11 mutants are deficient for meiotic recombination and are partially or completely sterile. Depending on the species, this reduced fertility reflects either a defect in chromosome segregation, or an arrest response in germ cell differentiation. Similarities and differences from species to species uncover a complex set of regulations that coordinate recombination with other events of meiotic prophase, such as chromosome pairing and meiotic cell cycle.

Atherosclerosis, oxidative stress and auto-antibodies in systemic lupus erythematosus and primary antiphospholipid syndrome

Overwhelming evidence spanning three decades has consistently shown that coronary artery disease is a major cause of morbidity and mortality in Systemic Lupus Erythematosus. Traditionally this was explained by abnormalities of the lipid profile induced by prolonged steroid treatment. Subsequently, antiphospholipid antibodies were presented as an additional cardiovascular risk factor. Recently, antibodies towards high-density lipoprotein and antiapolipoprotein A-I have been identified. These, together with anti-beta2 glycoprotein-1, interfere with the major antioxidant defence of patients with SLE and with primary antiphospholiqid syndrome exposing them to the atherogenic potential of enhanced oxidative stress. The present review discusses how the latter auto-antibodies, together with abnormalities of their target lipid auto-antigens, could enhance the risk of atherosclerosis in SLE and APS.

Differential association of SMC1alpha and SMC3 proteins with meiotic chromosomes in wild-type and SPO11-deficient male mice

SMC proteins are components of cohesin complexes that function in chromosome cohesion. We determined that SMC1alpha and SMC3 localized to wild-type mouse meiotic chromosomes, but with distinct differences in their patterns. Anti-SMC3 coincided with axial elements of the synaptonemal complex, while SMC1alpha was observed mainly in regions where homologues were synapsed. This pattern was especially visible in pachytene sex vesicles where SMC1alpha localized only weakly to the asynapsed regions. At diplotene, SMC3, but not SMC1alpha, remained bound along axial elements of desynapsed chromosomes. SMC1alpha and SMC3 were also found to localize along meiotic chromosome cores of Spo11 null spermatocytes, in which double-strand break formation required for DNA recombination and homologous pairing were disrupted. In Spo11 -/- cells, SMC1alpha localization differed from SMC3 again, confirming that SMC1alpha is mainly associated with homologous or non-homologous synapsed regions, whereas SMC3 localized throughout the chromosomes. Our results suggest that the two cohesin proteins may not always be associated in a dimer and may function as separate complexes in mammalian meiosis, with SMC1alpha playing a more specific role in synapsis. In addition, our results indicate that cohesin cores can form independently of double-strand break formation and homologous pairing.

The extracellular Phr peptide-Rap phosphatase signaling circuit of Bacillus subtilis

In the field of cell-cell communication, an emerging class of extracellular signaling peptides that function intracellularly has been identified in Gram-positive bacteria. One illustrative member of this group is the Phr family of extracellular signaling peptides of Bacillus subtilis. The Phr signaling peptides are secreted by the bacterium, and then, despite the presence of intracellular peptidases, they are actively transported into the cell where they interact with intracellular receptors to regulate gene expression. The intracellular receptors are members of a family of aspartyl-phosphate phosphatases, the Rap phosphatases. These phosphatases cause the dephosphorylation of response regulator proteins, ubiquitous regulatory proteins in bacteria. Immediately downstream of the genes for the Rap phosphatases are the genes for the Phr peptides, forming rap phr signaling cassettes. There are at least seven rap phr signaling cassettes in B. subtilis, and the genome sequence of other Gram-positive, endospore-forming bacteria suggests that similar cassettes may also function in these bacteria. In B. subtilis, the rap phr cassettes regulate sporulation, genetic competence, and genes comprising the quorum response (i.e. the response to high cell density). This review will address the mechanism of extracellular Phr signaling peptide production, transport, response, and their role in quorum sensing.

The Lipase Engineering Database: a navigation and analysis tool for protein families

The Lipase Engineering Database (LED) (http://www.led.uni-stuttgart.de) integrates information on sequence, structure, and function of lipases, esterases, and related proteins. Sequence data on 806 protein entries are assigned to 38 homologous families, which are grouped into 16 superfamilies with no global sequence similarity between each other. For each family, multisequence alignments are provided with functionally relevant residues annotated. Pre-calculated phylogenetic trees allow navigation inside superfamilies. Experimental structures of 45 proteins are superposed and consistently annotated. The LED has been applied to systematically analyze sequence-structure-function relationships of this vast and diverse enzyme class. It is a useful tool to identify functionally relevant residues apart from the active site residues, and to design mutants with desired substrate specificity.

Targeted stimulation of meiotic recombination

Meiotic recombination in Saccharomyces cerevisiae is initiated by programmed DNA double-strand breaks (DSBs), a process that requires the Spo11 protein. DSBs usually occur in intergenic regions that display open chromatin accessibility, but other determinants that control their frequencies and non-random chromosomal distribution remain obscure. We report that a Spo11 construct bearing the Gal4 DNA binding domain not only rescues spo11Delta spore inviability and catalyzes DSB formation at natural sites but also strongly stimulates DSB formation near Gal4 binding sites. At GAL2, a naturally DSB-cold locus, Gal4BD-Spo11 creates a recombinational hotspot that depends on all the other DSB gene functions, showing that the targeting of Spo11 to a specific site is sufficient to stimulate meiotic recombination that is under normal physiological control.

Decreased atherosclerotic lesion formation in human serum paraoxonase transgenic mice

BACKGROUND

Serum paraoxonase (PON1), an enzyme carried on HDL, inhibits LDL oxidation, and in human population studies, low PON1 activity is associated with atherosclerosis. In addition, PON1 knockout mice are more susceptible to lipoprotein oxidation and atherosclerosis. To evaluate whether PON1 protects against atherosclerosis and lipid oxidation in a dose-dependent manner, we generated and studied human PON1 transgenic mice.

METHODS AND RESULTS

Human PON1 transgenic mice were produced by using bacterial artificial chromosome genomic clones. The mice had 2- to 4-fold increased plasma PON1 levels, but plasma cholesterol levels were unchanged. Atherosclerotic lesions were significantly reduced in the transgenic mice when both dietary and apoE-null mouse models were used. HDL isolated from the transgenic mice also protected against LDL oxidation more effectively.

CONCLUSIONS

Our results indicate that PON1 protects against atherosclerosis in a dose-dependent manner and suggest that it may be a potential target for developing therapeutic agents for the treatment of cardiovascular disease.

Current progress on esterases: from molecular structure to function

This article reports on a symposium sponsored by the American Society for Pharmacology and Experimental Therapeutics and held at the April 2001 Experimental Biology meeting. Current developments in molecular-based studies into the structure and function of cholinesterases, carboxylesterases, and paraoxonases are described. This article covers mechanisms of regulation of gene expression of the various esterases by developmental factors and xenobiotics, as well as the interplay between physiological and chemical regulation of enzyme activity.

Codon 311 (Cys --> Ser) polymorphism of paraoxonase-2 gene is associated with apolipoprotein E4 allele in both Alzheimer's and vascular dementias

The gene of an esterase enzyme, called paraoxonase (PON, EC.3.1.8.1.) is a member of a multigene family that comprises three related genes PON1, PON2, and PON3 with structural homology clustering on the chromosome 7.(1,2) The PON1 activity and the polymorphism of the PON1 and PON2 genes have been found to be associated with risk of cardiovascular diseases such as hypercholesterolaemia, non-insulin-dependent diabetes, coronary heart disease (CHD) and myocardial infaction.(3-8) The importance of cardiovascular risk factors in the pathomechanism of Alzheimer's disease (AD) and vascular dementia (VD)(9-13) prompted us to examine the genetic effect of PON2 gene codon 311 (Cys-->Ser; PON2*S) polymorphism and the relationship between the PON2*S allele and the other dementia risk factor, the apoE polymorphism in these dementias. The PON2*C and PON2*S allele frequencies were similar in both AD (25% and 75%) and VD groups (23% and 77%), respectively, compared with the controls (27% and 73%). The ratio of the PON2*S carriers was significantly higher among the apoE4 allele carrier AD (27%) and VD (25%) groups than in the control (12%). Our results indicate that the PON2*S and apoE4 alleles have interactive effect on the development of the two most common forms of dementias AD and VD, and further support the hypothesis that cardiovascular factors contribute to the development of AD.

Wild-type levels of Spo11-induced DSBs are required for normal single-strand resection during meiosis

We have studied the repair of a DNA-DSB created by the VMA1-derived endonuclease in mutants that have different levels of Spo11-DSBs: WT (sae2), few (hop1), and none (spo11-Y135F). In spo11-Y135F and hop1 cells, intrachromosomal repair is more frequent than in WT and sae2 cells. In spo11-Y135F cells there was no chromosome pairing or synapsis and a faster turnover of resected DNA. Compared to WT and sae2 cells, spo11-Y135F and hop1 cells have a greater proportion of long resection tracts. The data suggest that high levels of Spo11-DSBs are required for normal regulation of resection, even at a DSB created by another protein. WT control over resection could be important for directing repair to be interchromosomal, increasing the chance of creating interhomolog connections essential to meiotic segregation.

Sex and the single (double-strand) break

It has been known for some time that DNA double-strand breaks (DSBs) initiate homologous recombination during meiosis. Two recent studies show that the fate of a single DSB in yeast is strongly influenced by the presence of other breaks in the genome, hinting that cell-wide or chromosome-regional mechanisms control the outcome of DSB repair.

Most meiotic CAG repeat tract-length alterations in yeast are SPO11 dependent

The expansion of trinucleotide repeat sequences associated with hereditary neurological diseases is believed from earlier studies to be due to errors in DNA replication. However, more recent studies have indicated that recombination may play a significant role in triplet repeat expansion. CAG repeat tracts have been shown to induce double-strand breaks (DSBs) during meiosis in yeast, and DSB formation is dependent on the meiotic recombination machinery. The rate of meiotic instability is several fold higher than mitotic instability. To determine whether DSB repair is responsible for the high rate of repeat tract-length alterations, the frequencies of meiotic repeat-tract instability were compared in wild-type and spo11 mutant strains. In the spo11 background, the rate of meiotic repeat-tract instability remained at the mitotic level, suggesting that meiotic alterations of CAG repeat tracts in yeast occur by the recombination mechanism. Several of these meiotic tract-length alterations are due to DSB repair involving use of the sister chromatid as a template.

Paraoxonase 1 overexpression in mice and its effect on high-density lipoproteins

Paraoxonase (PON1) is a high-density lipoprotein (HDL)-associated enzyme believed to protect against the early events of atherogenesis by its ability to hydrolyze oxidized phospholipids. A transgenic mouse overexpressing PON1 (mPON1) was developed to address the question of whether overexpression of PON1 is important in protecting HDL function during oxidative stress. Transgenic mice were obtained that have up to a 5-fold increase in mPON1 activity measured as arylesterase activity [52.7 +/- 17.3 U/ml versus 251.7 +/- 25.1 U/ml for wild-type (WT) and mPON1 high expressers, respectively]; this increase in mPON1 activity was reflected by a 5.3-fold increase in relative mass of the enzyme. Excess mPON1 was associated solely with HDL but did not alter HDL composition, size, or charge. Lecithin:cholesterol acyltransferase (LCAT) on HDL is a sensitive indicator of oxidative stress; exposure of plasmas from both WT and mPON1 overexpresser mice to 0.4 mM copper ions for 2 h showed a 30-40% protection of LCAT activity in mPON1 overexpressers compared to WT. Excess mPON1 also inhibited lipid hydroperoxide formation on HDL. These data strongly suggest that overexpression of mPON1 protects HDL integrity and function.

Functional interactions between SPO11 and REC102 during initiation of meiotic recombination in Saccharomyces cerevisiae

In Saccharomyces cerevisiae, formation of the DNA double-strand breaks (DSBs) that initiate meiotic recombination requires the products of at least 10 genes. Spo11p is thought to be the catalytic subunit of the DNA cleaving activity, but the roles of the other proteins, and the interactions among them, are not well understood. This study demonstrates genetic and physical interactions between the products of SPO11 and another early meiotic gene required for DSB formation, REC102. We found that epitope-tagged versions of SPO11 and REC102 that by themselves were capable of supporting normal or nearly normal levels of meiotic recombination conferred a severe synthetic cold-sensitive phenotype when combined in the same cells. DSB formation, meiotic gene conversion, and spore viability were drastically reduced in the doubly tagged strain at a nonpermissive temperature. This conditional defect could be partially rescued by expression of untagged SPO11, but not by expression of untagged REC102, indicating that tagged REC102 is fully dominant for this synthetic phenotype. Both tagged and wild-type Spo11p co-immunoprecipitated with tagged Rec102p from meiotic cell extracts, indicating that these proteins are present in a common complex in vivo. Tagged Rec102p localized to the nucleus in whole cells and to chromatin on spread meiotic chromosomes. Our results are consistent with the idea that a multiprotein complex that includes Spo11p and Rec102p promotes meiotic DSB formation.

Paraoxonase-2 is a ubiquitously expressed protein with antioxidant properties and is capable of preventing cell-mediated oxidative modification of low density lipoprotein

The oxidation of apolipoprotein B-containing lipoproteins and cell membrane lipids is believed to play an integral role in the development of fatty streak lesions, an initial step in atherogenesis. We have previously shown that two antioxidant-like enzymes, paraoxonase (PON)-1 and PON3, are high density lipoprotein-associated proteins capable of preventing the oxidative modification of low density lipoprotein (LDL) (Reddy, S. T., Wadleigh, D. J., Grijalva, V., Ng, C., Hama, S., Gangopadhyay, A., Shih, D. M., Lusis, A. J., Navab, M., and Fogelman, A. M. (2001) Arterioscler. Thromb. Vasc. Biol. 21, 542-547). In the present study, we demonstrate that PON2 (i) is not associated with high density lipoprotein; (ii) has antioxidant properties; and (iii) prevents LDL lipid peroxidation, reverses the oxidation of mildly oxidized LDL (MM-LDL), and inhibits the ability of MM-LDL to induce monocyte chemotaxis. The PON2 protein was overexpressed in HeLa cells using the tetracycline-inducible ("Tet-On") system, and its antioxidant capacity was measured in a fluorometric assay. Cells that overexpressed PON2 showed significantly less intracellular oxidative stress following treatment with hydrogen peroxide or oxidized phospholipid. Moreover, cells that overexpressed PON2 were also less effective in oxidizing and modifying LDL and, in fact, were able to reverse the effects of preformed MM-LDL. Our results suggest that PON2 possesses antioxidant properties similar to those of PON1 and PON3. However, in contrast to PON1 and PON3, PON2 may exert its antioxidant functions at the cellular level, joining the host of intracellular antioxidant enzymes that protect cells from oxidative stress.

Paraoxonase genotype modifies the effect of pravastatin on high-density lipoprotein cholesterol

Paraoxonase (PON) is an enzyme carried by high-density lipoprotein cholesterol (HDL-C). Two gene polymorphisms leading to amino acid substitutions of methionine for leucine at position 55 (M/L55) and arginine for glutamine at position 192 (R/Q192) modulate the activity of the enzyme and possibly also lipid and apolipoprotein concentrations. Our purpose was to examine the effect of the PON genotype on HDL-C and apolipoprotein AI (apo AI) responses to pravastatin treatment. Fifty-one mildly hypercholesterolemic male subjects (mean age 35 +/- 4 years) were enrolled by this prospective, randomized, double-blind study. Lipid concentrations were measured at baseline and after 6 months of pravastatin (n = 25) or placebo (n = 26) therapy. Low active (MM, ML or QQ) and high active (LL or RQ, RR) PON genotype groups were related to lipid and apolipoprotein concentration changes. Pravastatin increased the apo AI concentration 12% (P = 0.017, RANOVA) and tended to increase the HDL-C concentration (P = 0.095, RANOVA) in R allele carriers but not in QQ homozygotes. Significant predictors of the change in apo AI concentration during pravastatin treatment were R/Q192 genotype (P = 0.002), apo AI concentration at baseline (P = 0.002) and M/L55 genotype (P = 0.042). Correspondingly, R/Q192 (P = 0.009) and M/L55 (P = 0.050) genotypes were the statistically significant determinants of HDL-C concentration change. The PON genotype thus modifies the effect of pravastatin on serum HDL-C and apo AI concentrations. This could partly explain the contradictory results obtained from previous studies on the effects of statins on the serum HDL-C concentration.

Optimization of metabolic stability as a goal of modern drug design

Metabolism and other pharmacokinetic (PK) studies have always played a critical role in helping to optimize the bioavailability and duration of action of new drugs thereby increasing their success rate. With the advent of automated combinatorial synthesis, high-throughput pharmacological testing, and the ability to create extensive databases in the past decade, drug discovery has undergone an amazing evolution. With the increased throughput of drug discovery, metabolism and other PK studies have evolved to keep pace. Often called "early ADME" studies, these studies are characterized by parallel processing and higher throughput than before. This article focuses on a particular class of early ADME (absorption, distribution mechanism, and excretion) studies known as "metabolic stability" studies. The theoretical basis for metabolic stability and its relationship to the concept of metabolic intrinsic clearance is briefly presented. Some key relationships between structure and metabolism are summarized. Several case studies from recent medicinal chemistry literature are reviewed to exemplify how metabolic stability studies influenced drug design and led to improvements in bioavailability and half-life. Finally, future trends in drug metabolism and analytical chemistry and how they may influence metabolic stability studies are reviewed.

Paraoxonase and atherosclerosis

There is considerable evidence that the antioxidant activity of high density lipoprotein (HDL) is largely due to the paraoxonase-1 (PON1) located on it. Experiments with transgenic PON1 knockout mice indicate the potential for PON1 to protect against atherogenesis. This protective effect of HDL against low density lipoprotein (LDL) lipid peroxidation is maintained longer than is the protective effect of antioxidant vitamins and could thus be more important. There is evidence that the genetic polymorphisms of PON1 least able to protect LDL against lipid peroxidation are overrepresented in coronary heart disease, particularly in association with diabetes. However, these polymorphisms explain only part of the variation in serum PON1 activity; thus, a more critical test of the hypothesis is likely to be whether low serum PON1 activity is associated with coronary heart disease. Preliminary case-control evidence suggests that this is indeed the case and, thus, that the quest for dietary and pharmacological means of modifying serum PON1 activity may allow the oxidant model of atherosclerosis to be tested in clinical trials.