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Biomedical subjects

C Monnier

Publications and source records attributed to C Monnier.

At least 19 recordsLinked to original sources
PubMed2001

Crystal structures of two human pyrophosphorylase isoforms in complexes with UDPGlc(Gal)NAc: role of the alternatively spliced insert in the enzyme oligomeric assembly and active site architecture.

The recently published human genome with its relatively modest number of genes has highlighted the importance of post-transcriptional and post-translational modifications, such as alternative splicing or glycosylation, in generating the complexities of human biology. The human UDP-N-acetylglucosamine (UDPGlcNAc) pyrophosphorylases AGX1 and AGX2, which differ in sequence by an alternatively spliced 17 residue peptide, are key enzymes synthesizing UDPGlcNAc, an essential precursor for protein glycosylation. To better understand the catalytic mechanism of these enzymes and the role of the alternatively spliced segment, we have solved the crystal structures of AGX1 and AGX2 in complexes with UDPGlcNAc (at 1.9 and 2.4 A resolution, respectively) and UDPGalNAc (at 2.2 and 2.3 A resolution, respectively). Comparison with known structures classifies AGX1 and AGX2 as two new members of the SpsA-GnT I Core superfamily and, together with mutagenesis analysis, helps identify residues critical for catalysis. Most importantly, our combined structural and biochemical data provide evidence for a change in the oligomeric assembly accompanied by a significant modification of the active site architecture, a result suggesting that the two isoforms generated by alternative splicing may have distinct catalytic properties.

Alternative Splicing↗
PubMed2001

A novel gene from Myxococcus xanthus that facilitates membrane translocation of an extracellular endoglucanase in Escherichia coli?

Expression in Escherichia coli of the Myxococcus xanthus gene celA, which encodes an extracellular endoglucanase, resulted in CelA being distributed between cytoplasm, periplasm and membrane. The presence of an adjacent open reading frame downstream from the full celA gene, or the absence of a putative lipoprotein signal sequence, confined CelA distribution to the periplasm and membrane, or to the cytoplasm and periplasm, respectively.

Amino Acid Sequence↗
PubMed2000

Submolecular Structures in Dipalmytoylphosphatidylethanolamine Langmuir-Blodgett Films Observed by Scanning Force Microscopy.

Dipalmitoylphosphatidylethanolamine (DDPE) Langmuir films at the air/water interface have been studied. These films exhibit high stability. The resulting films transferred on muscovite have been studied by scanning force microscopy with the contact mode. At the microscopic scale, DDPE Langmuir-Blodgett films appear densely packed with few defects. At molecular resolution the films appear well ordered; the double tail of the lipids has been observed.d Copyright 2000 Academic Press.

Journal Article↗
PubMed1997

Hypothesis: the meeting place model for prion disease.

Prions are responsible for spongiform diseases such as scrapie and bovine spongiform encephalopathy. It is now generally accepted that the disease mechanism involves the conversion from the normal form, PrPC, to the pathogenic form, PrPSc, and that this isoform is infectious. In the case of scrapie, 15 different forms of the disease have been described and some of these different phenotypes can be conferred by infectious prions that are themselves encoded by normal genes. We propose here that a prion with an altered structure has a correspondingly altered preference for lipids; this altered preference creates a proteolipid domain containing different lipids and other factors such as chaperonins and enzymes responsible for post-translational modifications. Normal prions associated with this abnormal domain adopt the conformation dictated by its lipidic composition (and by the other factors present) and so acquire the lipidic preference of the original pathogenic prions. These transformed prions could then create new proteolipid domains. This process may be considered as semi-conservative replication in which prion and lipids are analogous to the Watson and Crick strands and the proteolipid domain to the double helix itself.

Animals↗
PubMed1996

Spatial learning in a Z-maze by cerebellar mutant mice.

Two types of cerebellar mutant mice (staggerer and lurcher) were evaluated during 5-day acquisition of a spatial learning task in a Z-maze filled with water. Although the number of errors and escape latencies decreased in normal mice, the acquisition of the cerebellar mutants was impaired but not abolished. These results indicate that the cerebellum has a role in spatial learning. Mice with cerebellar dysfunction take a more indirect route toward a goal during the course of swimming, when ataxic symptoms are no longer in evidence.

Animals↗
PubMed1995

Elevated (+)-maze and hole-board exploration in lurcher mutant mice.

The behavior of lurcher mice, a mutant with degeneration of cerebellar cells, was compared to that of normal mice for three days in two tests of exploration; an elevated (+)-maze and a 4 x 4 hole-board. In the elevated (+)-maze, lurcher mutants visited fewer closed arms than normal mice only on the first test day. Lurcher mutants were slower to emerge from the first closed arm but did not differ from normal mice for entry latencies into the first open arm. The time spent by the mutants in the open arms was higher than that of normal mice, an indication of decreased inhibition to open spaces. In the hole-board, lurcher mutants visited fewer holes than normal mice only on the first day of testing. In proportion to the total number of holes explored, lurcher mutants visited fewer center holes and fewer holes situated next to each other. These results may be due to a lesion-induced tendency to explore a more restricted region of a novel spatial environment and to explore it in a more haphazard fashion.

Animals↗
PubMed1993

Mutations in two new loci that impair both extracellular protein production and development in Myxococcus xanthus.

Two transposon insertion mutants of Myxococcus xanthus altered in the secretion of protein as determined by the hydrolytic activities of several enzymes during vegetative growth were also unable to complete fruiting body formation and were severely impaired in sporulation. The insertions were located in the same part of the M. xanthus chromosome but were unlinked by transduction and therefore define two distinct loci, called excA and excB. Since both Exc +/- mutants were able to rescue development of an asgB mutation, they do not belong to the Asg- group, despite of the fact that asg mutants are also Exc +/-. Our results sustain the hypothesis of a possible relationship between protein secretion during vegetative growth and development or sporulation.

Bacterial Proteins↗
PubMed1990

Mechanism of integration of the broad-host-range plasmid RP4 into the chromosome of Myxococcus xanthus.

The site-specific recombination mechanism through which the plasmid RP4 has been previously shown to integrate into the chromosome of Myxococcus xanthus has been investigated further. Once integrated in one of the numerous chromosomal sites from two different strains, through a precise site on the plasmid, the latter can be excised either precisely or after a definite 14.5-kb deletion. In some cases, the integration is followed by different DNA rearrangements that yield a higher rate of excision and integration. A model for the site-specific integration and excision of the plasmid is proposed.

Blotting, Southern↗
PubMed1990

Comparison of beta-galactosidase production by two inducible promoters in Myxococcus xanthus.

The inducibility of two promoter systems, one heterologous and one homologous, has been assessed in the Gram-negative bacterium Myxococcus xanthus. The heterologous system involved the hybrid tac promoter and the presence of lacIq, the lac repressor from Escherichia coli. This system is inducible in its natural host with isopropyl-beta-D-thiogalactopyranoside (IPTG). The homologous promoter system involves the light-inducible carQRS promoter, which is normally involved in the expression of the regulators of the light-inducible light-protective carotenoid synthesis regulon in M. xanthus. In each case, promoter activity and strength was assayed using the E. coli gene lacZ. In our constructs, which were present in a single copy in the M. xanthus chromosome, the carQRS promoter yielded at least a 47-fold increase in beta-galactosidase production upon light induction, whilst IPTG increased by 8-fold the amount of enzyme produced under the control of the ptac-lacIq system. Regulation by the latter was significantly higher than that obtained with the unmodified lacZ promoter.

Enzyme Induction↗
PubMed1981

Epidemiology of Duchenne muscular dystrophy in the province of Turin.

An epidemiological investigation on Duchenne muscular dystrophy in Turin and its province has been carried out for the period 1955-974. The incidence of the disease proved to be 24 X 10(-5), and the prevalence 2.15 X 10(-5). The mutation rate was 80 X 10(-6). The data are compared with the literature. Segregation analysis on many families was performed in order to find the theoretical number of carrier among Duchenne mothers. The importance of epidemiology for genetic counselling is stressed.

Child↗
PubMed1980

Enzyme activities associated with an invertebrate iridovirus: protein kinase activity associated with iridescent virus type 6 (chilo iridescent virus).

Iridescent virus type 6 was found to contain an endogenous protein kinase activity which can phosphorylate some viral proteins and exogenous basic proteins. The enzyme required a divalent metal ion but was not stimulated by cyclic nucleotides. Procedures which are known to solubilize the viral envelope indicated that the protein kinase was an internal component of the virion. Conditions for protein kinase activity are described.

Journal Article↗
PubMed1978

[Prolonged glomerulonephritis and cyanotic heart disease].

Three children with congenital heart disease presented with more or less severe renal dysfunction. Histologic studies showed signs of membranoproliferative pseudoglomerulonephritis without deposits on immunofluorescence. Surgical correction of the heart defect induced a spectacular functional and histologic improvement.

Adolescent↗