Richard M

References (3)

Title : Cyclipostins and cyclophostin analogs inhibit the antigen 85C from Mycobacterium tuberculosis both in vitro and in vivo - Viljoen_2018_J.Biol.Chem_293_2755
Author(s) : Viljoen A , Richard M , Nguyen PC , Fourquet P , Camoin L , Paudal RR , Gnawali GR , Spilling CD , Cavalier JF , Canaan S , Blaise M , Kremer L
Ref : Journal of Biological Chemistry , 293 :2755 , 2018
Abstract : An increasing prevalence of cases of drug-resistant tuberculosis requires the development of more efficacious chemotherapies. We previously reported the discovery of a new class of cyclipostins and cyclophostin (CyC) analogs exhibiting potent activity against Mycobacterium tuberculosis both in vitro and in infected macrophages. Competitive labeling/enrichment assays combined with MS have identified several serine or cysteine enzymes in lipid and cell wall metabolism as putative targets of these CyC compounds. These targets included members of the antigen 85 (Ag85) complex (i.e. Ag85A, Ag85B, and Ag85C), responsible for biosynthesis of trehalose dimycolate and mycolylation of arabinogalactan. Herein, we used biochemical and structural approaches to validate the Ag85 complex as a pharmacological target of the CyC analogs. We found that CyC7beta, CyC8beta, and CyC17 bind covalently to the catalytic Ser(124) residue in Ag85C; inhibit mycolyltransferase activity (i.e. the transfer of a fatty acid molecule onto trehalose); and reduce triacylglycerol synthase activity, a property previously attributed to Ag85A. Supporting these results, an X-ray structure of Ag85C in complex with CyC8beta disclosed that this inhibitor occupies Ag85C's substrate-binding pocket. Importantly, metabolic labeling of M. tuberculosis cultures revealed that the CyC compounds impair both trehalose dimycolate synthesis and mycolylation of arabinogalactan. Overall, our study provides compelling evidence that CyC analogs can inhibit the activity of the Ag85 complex in vitro and in mycobacteria, opening the door to a new strategy for inhibiting Ag85. The high-resolution crystal structure obtained will further guide the rational optimization of new CyC scaffolds with greater specificity and potency against M. tuberculosis.
ESTHER : Viljoen_2018_J.Biol.Chem_293_2755
PubMedSearch : Viljoen_2018_J.Biol.Chem_293_2755
PubMedID: 29301937
Gene_locus related to this paper: myctu-a85c

Title : A mesocosm study of fate and effects of CuO nanoparticles on endobenthic species (Scrobicularia plana, Hediste diversicolor) - Buffet_2013_Environ.Sci.Technol_47_1620
Author(s) : Buffet PE , Richard M , Caupos F , Vergnoux A , Perrein-Ettajani H , Luna-Acosta A , Akcha F , Amiard JC , Amiard-Triquet C , Guibbolini M , Risso-De Faverney C , Thomas-Guyon H , Reip P , Dybowska A , Berhanu D , Valsami-Jones E , Mouneyrac C
Ref : Environ Sci Technol , 47 :1620 , 2013
Abstract : The fate and effects of CuO nanoparticles (CuO NPs) were examined in endobenthic species (Scrobicularia plana , Hediste diversicolor), under environmentally realistic conditions in outdoor mesocosms (exposure to Cu at 10 mug L(-1) in particulate (CuO NPs) or soluble salt (CuNO(3)) forms) for 21 days. Labile Cu was determined in water and sediment by using diffusive gradient in thin films. No labile Cu being detected from CuO NPs; the observed effects in invertebrates exposed to CuO NPs were mainly attributed to the toxicity of nanoparticulate rather than dissolved Cu toxicity. Bioaccumulation of CuO NPs was observed in both species. Biomarkers were examined at different levels of biological organization: biochemical markers of defense and damage, biomarkers of genotoxicity (comet assay), and behavioral biomarkers (feeding and burrowing). Behavioral biomarkers, antioxidant defenses (catalase, glutathion S-transferase, metallothionein), and genotoxicity are the most sensitive tools to highlight the effect of soluble or nanoparticulate metal forms. Concerning other biomarkers of defense (superoxide dismutase, lactate dehydrogenase, laccase) and damage (thiobarbituric acid reactive substances, acetylcholinesterase, acid phosphatase), no significant effects were detected. This experiment shows the suitability of mesocosms for studying the environmental effects of nanoparticles.
ESTHER : Buffet_2013_Environ.Sci.Technol_47_1620
PubMedSearch : Buffet_2013_Environ.Sci.Technol_47_1620
PubMedID: 23240726

Title : Biosynthesis of ionotropic acetylcholine receptors requires the evolutionarily conserved ER membrane complex - Richard_2013_Proc.Natl.Acad.Sci.U.S.A_110_E1055
Author(s) : Richard M , Boulin T , Robert VJ , Richmond JE , Bessereau JL
Ref : Proc Natl Acad Sci U S A , 110 :E1055 , 2013
Abstract : The number of nicotinic acetylcholine receptors (AChRs) present in the plasma membrane of muscle and neuronal cells is limited by the assembly of individual subunits into mature pentameric receptors. This process is usually inefficient, and a large number of the synthesized subunits are degraded by endoplasmic reticulum (ER)-associated degradation. To identify cellular factors required for the synthesis of AChRs, we performed a genetic screen in the nematode Caenorhabditis elegans for mutants with decreased sensitivity to the cholinergic agonist levamisole. We isolated a partial loss-of-function allele of ER membrane protein complex-6 (emc-6), a previously uncharacterized gene in C. elegans. emc-6 encodes an evolutionarily conserved 111-aa protein with two predicted transmembrane domains. EMC-6 is ubiquitously expressed and localizes to the ER. Partial inhibition of EMC-6 caused decreased expression of heteromeric levamisole-sensitive AChRs by destabilizing unassembled subunits in the ER. Inhibition of emc-6 also reduced the expression of homomeric nicotine-sensitive AChRs and GABAA receptors in C. elegans muscle cells. emc-6 is orthologous to the yeast and human EMC6 genes that code for a component of the recently identified ER membrane complex (EMC). Our data suggest this complex is required for protein folding and is connected to ER-associated degradation. We demonstrated that inactivation of additional EMC members in C. elegans also impaired AChR synthesis and induced the unfolded protein response. These results suggest that the EMC is a component of the ER folding machinery. AChRs might provide a valuable proxy to decipher the function of the EMC further.
ESTHER : Richard_2013_Proc.Natl.Acad.Sci.U.S.A_110_E1055
PubMedSearch : Richard_2013_Proc.Natl.Acad.Sci.U.S.A_110_E1055
PubMedID: 23431131