Evidence for a defect of holocarboxylase synthetase activity in cultured lymphoblasts from a patient with biotin-responsive multiple carboxylase deficiency.

We report here the expression of biotin-responsive multiple carboxylase deficiency in cultured lymphoblasts of a patient whose fibroblasts belong to the bio genetic complementation group. Cultured lymphoblasts from the patient lost propionyl-CoA carboxylase (PCC) and beta-methylcrotonyl-CoA carboxylase (MCC) activities at a faster rate than normal cells when grown in biotin-deficient medium. Recovery of normal PCC and MCC activities, which was independent of protein synthesis, required a 2,500-fold higher biotin concentration than that required by normal lymphoblasts. Holocarboxylase synthetase activity was detected in cell-free extracts through the biotinylation of endogenous apo-PCC in the presence of ATP to form active holo-PCC. While the apo-PCC in extracts of normal biotin-starved lymphoblasts could be activated to 28% of maximal activity, extracts of patient lymphoblasts did not exhibit any ATP and biotin-dependent increase in PCC activity. A normal cell extract, cleared of apocarboxylases by immunoprecipitation, stimulated the PCC activity of a patient cell extract 20-fold. These results indicate that the apoenzyme in bio cells is normal and that the defect lies in the holocarboxylase synthetase.     

β-hexosaminidase immunolocalization and α- and β-subunit gene expression in the rat testis and epididymis

β-hexosaminidase is an essential lysosomal enzyme whose absence in man results in a group of disorders, the G_M2 gangliosidoses. β-hexosaminidase activity is many times higher in the epididymis than in other tissues, is present in sperm, and is postulated to be required for mammalian fertilization. To better understand which cells are responsible for β-hexosaminidase expression and how it is regulated in the male reproductive system, we quantitated the mRNA expression of the α- and β-subunits of β-hexosaminidase and carried out immunocytochemical localization studies of the enzyme in the rat testis and epididymis. β-hexosaminidase α-subunit mRNA was abundant and differentially expressed in the adult rat testis and epididymis, at 13- and 2-fold brain levels, respectively. In contrast, β-subunit mRNA levels in the testis and epididymis were 0.3- and 5-fold brain levels. During testis development from 7–91 postnatal days of age, testis levels of α-subunit mRNA increased 10-fold and coincided with the appearance of spermatocytes and spermatids in the epithelium; in contrast, β-subunit mRNA was expressed at low levels throughout testis development. In isolated male germ cells, β-hexosaminidase α-subunit expression was most abundant in haploid round spermatids, whereas the β-subunit mRNA was not detected in germ cells. Within the epididymis both α- and β-subunit mRNA concentrations were highest in the corpus, with 1.5-fold and 9-fold initial segment values, respectively. Light microscopic immunocytochemistry revealed that β-hexosaminidase was localized to Sertoli cells and interstitial macrophages in the testis. In the epididymis, β-hexosaminidase staining was most intense in narrow cells in the initial segment, principal cells in the caput, and proximal corpus, and clear cells throughout the duct. Electron microscopic immunocytochemistry revealed that β-hexosaminidase was predominantly present in lysosomes in Sertoli and epididymal cells. The cellular and regional specificity of β-hexosaminidase immunolocalization suggest an important role for the enzyme in testicular and epididymal functions. Mol. Reprod. Dev. 46:227–242, 1997. © 1997 Wiley-Liss, Inc.     

Time-resolved fluorescence resonance energy transfer shows that the bacterial multidrug ABC half-transporter BmrA functions as a homodimer

Members of the ATP-binding cassette (ABC) transporters share the same basic architecture, with a four-core domain made of two transmembrane plus two nucleotide-binding domains. However, a supramolecular organization has been detected in some ABC transporters, which might be relevant to physiological regulation of substrate transport. Here, the oligomerization status of a bacterial half-ABC multidrug transporter, BmrA, was investigated. Each BmrA monomer containing a single cysteine residue introduced close to either the Walker A or the ABC signature motifs was labeled using two probes, 2-(4-maleimidoanilino)naphthalene-6-sulfonic acid (fluorescence donor) or 4-dimethylaminophenylazophenyl-4'-maleimide (fluorescence acceptor). Reconstitution into proteoliposomes of BmrA monomers labeled separately with either the fluorescence donor or the fluorescence acceptor allowed measurement of time-resolved fluorescence resonance energy transfer between the two probes, showing that efficient reassociation of the singly labeled BmrA monomers occurred upon reconstitution. The efficiency of energy transfer studied as a function of increasing concentration of BmrA-labeled with the fluorescence acceptor argues for a dimeric association of BmrA instead of a tetrameric one. Furthermore, the efficiency of energy transfer allowed estimation of the distances between the two bound probes. Results suggest that, in the resting state, BmrA in a lipid bilayer environment preferentially adopts a closed conformation similar to that found in the BtuCD crystal structure and that the presence of different effectors does not substantially modify its global conformation.     

Antagonist Microorganisms with the Ability to Control <Emphasis Type="Italic">Pythium</Emphasis> Damping-off of Tomato Seeds in Rockwool

A total of 237 microorganisms were isolated from five different greenhouse tomato growing media. Of those, 40 microorganisms reduced the in vitro mycelial growth of both Pythium aphanidermatum and Pythium ultimum. The ability of these microorganisms to control damping-off was then tested in rockwool. As a result, Pseudomonas corrugata strains 1 and 3, Pseudomonas fluorescens subgroup F and G strains 1, 2, 3, 4 and 5, Pseudomonas marginalis, Pseudomonas putida subgroup B strain 1, Pseudomonas syringae strain 1 and Pseudomonas viridiflava significantly reduced damping-off caused by P. ultimum or P. aphanidermatum. Pseudomonas marginalis was the only microorganism that significantly reduced damping-off caused by both pathogens.     

Newcastle disease virus HN protein alters the conformation of the F protein at cell surfaces

Conformational changes in the Newcastle disease virus (NDV) fusion (F) protein during activation of fusion and the role of HN protein in these changes were characterized with a polyclonal antibody. This antibody was raised against a peptide with the sequence of the amino-terminal half of the F protein HR1 domain. This antibody immunoprecipitated both F(0) and F(1) forms of the fusion protein from infected and transfected cell extracts solubilized with detergent, and precipitation was unaffected by expression of the HN protein. In marked contrast, this antibody detected significant conformational differences in the F protein at cell surfaces, differences that depended upon HN protein expression. The antibody minimally detected the F protein, either cleaved or uncleaved, in the absence of HN protein expression. However, when coexpressed with HN protein, an uncleaved mutant F protein bound the anti-HR1 antibody, and this binding depended upon the coexpression of specifically the NDV HN protein. When the cleaved wild-type F protein was coexpressed with HN protein, the F protein bound anti-HR1 antibody poorly although significantly more than F protein expressed alone. Anti-HR1 antibody inhibited the fusion of R18 (octadecyl rhodamine B chloride)-labeled red blood cells to syncytia expressing HN and wild-type F proteins. This inhibition showed that fusion-competent F proteins present on surfaces of syncytia were capable of binding anti-HR1. Furthermore, only antibody which was added prior to red blood cell binding could inhibit fusion. These results suggest that the conformation of uncleaved cell surface F protein is affected by HN protein expression. Furthermore, the cleaved F protein, when coexpressed with HN protein and in a prefusion conformation, can bind anti-HR1 antibody, and the anti-HR1-accessible conformation exists prior to HN protein attachment to receptors on red blood cells.     

Expression in Escherichia coli of N- and C-terminally deleted human holocarboxylase synthetase. Influence of the N-terminus on biotinylation and identification of a minimum functional protein

Biotin functions as a covalently bound cofactor of biotindependent carboxylases. Biotin attachment is catalyzed by biotin protein ligases, called holocarboxylase synthetase in mammals and BirA in prokaryotes. These enzymes show a high degree of sequence similarity in their biotinylation domains but differ markedly in the length and sequence of their N terminus. BirA is also the repressor of the biotin operon, and its DNA attachment site is located in its N terminus. The function of the eukaryotic N terminus is unknown. Holocarboxylase synthetase with N- and C-terminal deletions were evaluated for the ability to catalyze biotinylation after expression in Escherichia coli using bacterial and human acceptor substrates. We showed that the minimum functional protein is comprised of the last 349 of the 726-residue protein, which includes the biotinylation domain. Significantly, enzyme containing intermediate length, N-terminal deletions interfered with biotin transfer and interaction with different peptide acceptor substrates. We propose that the N terminus of holocarboxylase synthetase contributes to biotinylation through N- and C-terminal interactions and may affect acceptor substrate recognition. Our findings provide a rationale for the biotin responsiveness of patients with point mutations in the N-terminal sequence of holocarboxylase synthetase. Such mutant enzyme may respond to biotin-mediated stabilization of the substrate-bound complex.     

IL-4 (B cell stimulatory factor 1) overcomes Fc gamma receptor-mediated inhibition of mouse B lymphocyte proliferation without affecting inhibition of c-myc mRNA induction

Mouse B cells are stimulated to proliferate by Fab'2 fragments of rabbit anti-mouse Ig antibodies. Proliferation is inhibited, however, in the presence of IgG anti-mouse Ig. We have previously shown that this inhibition is mediated by binding of the IgG anti-Ig to receptors for Fc gamma R on B cells. This report describes conditions under which IgG anti-mu or anti-delta will induce proliferation despite Fc gamma R engagement. Culture supernatants of Con A-stimulated, Il-4-secreting Th cell lines, but not of Il-2-secreting Th cell lines, will co-stimulate with IgG anti-Ig to induce small B cells to incorporate [3H]TdR. This co-mitogenic activity is inhibitable by anti-IL-4 antibodies and can also be induced by Il-4 affinity purified from the T cell supernatants or by supernatants containing rIl-4. B cells precultured with Il-4 for 18 h, while still expressing normal levels of Fc gamma R, also proliferate to IgG anti-Ig. We have previously shown that Fc gamma R-mIg cross-linking will inhibit mIg-dependent increases in c-myc mRNA levels. We investigated whether Il-4 allows B cells to respond to IgG anti-Ig by elevating c-myc. The data show that Il-4 has little effect on c-myc mRNA levels in either IgG or Fab'2 anti-Ig-containing cultures.     

Barriers in Referring Neonatal Patients to Perinatal Palliative Care: A French Multicenter Survey

BackgroundWhen an incurable fetal condition is detected, some women (or couples) would rather choose to continue with the pregnancy than opt for termination of pregnancy for medical reasons, which, in France, can be performed until full term. Such situations are frequently occurring and sometimes leading to the implementation of neonatal palliative care. The objectives of this study were to evaluate the practices of perinatal care french professionals in this context; to identify the potential obstacles that might interfere with the provision of an appropiate neonatal palliative care; and, from an opposite perspective, to determine the criteria that led, in some cases, to offer this type of care for prenatally diagnosed lethal abnormality.MethodsWe used an email survey sent to 434 maternal-fetal medicine specialists (MFMs) and fetal care pediatric specialists (FCPs) at 48 multidisciplinary centers for prenatal diagnosis (MCPD).ResultsForty-two multidisciplinary centers for prenatal diagnosis (87.5%) took part. In total, 102 MFMs and 112 FCPs completed the survey, yielding response rate of 49.3%. One quarter of professionals (26.2%) estimated that over 20% of fetal pathologies presenting in MCPD could correspond to a diagnosis categorized as lethal (FCPs versus MFMs: 24% vs 17.2%, p = 0.04). The mean proportion of fetal abnormalities eligible for palliative care at birth was estimated at 19.30% (± 2.4) (FCPs versus MFMs: 23.4% vs 15.2%, p = 0.029). The degree of diagnostic certainty appears to be the most influencing factor (98.1%, n = 207) in the information provided to the pregnant woman with regard to potential neonatal palliative care. The vast majority of professionals, 92.5%, supported considering the practice of palliative care as a regular option to propose antenatally.ConclusionsOur study reveals the clear need for training perinatal professionals in perinatal palliative care and for the standardization of practices in this field.     

Trait positions for elevated invasiveness in adaptive ecological networks

Our ability to predict the outcome of invasion declines rapidly as non-native species progress through intertwined ecological barriers to establish and spread in recipient ecosystems. This is largely due to the lack of systemic knowledge on key processes at play as species establish self-sustaining populations within the invaded range. To address this knowledge gap, we present a mathematical model that captures the eco-evolutionary dynamics of native and non-native species interacting within an ecological network. The model is derived from continuous-trait evolutionary game theory (i.e., Adaptive Dynamics) and its associated concept of invasion fitness which depicts dynamic demographic performance that is both trait mediated and density dependent. Our approach allows us to explore how multiple resident and non-native species coevolve to reshape invasion performance, or more precisely invasiveness, over trait space. The model clarifies the role of specific traits in enabling non-native species to occupy realised opportunistic niches. It also elucidates the direction and speed of both ecological and evolutionary dynamics of residing species (natives or non-natives) in the recipient network under different levels of propagule pressure. The versatility of the model is demonstrated using four examples that correspond to the invasion of (i) a horizontal competitive community; (ii) a bipartite mutualistic network; (iii) a bipartite antagonistic network; and (iv) a multi-trophic food web. We identified a cohesive trait strategy that enables the success and establishment of non-native species to possess high invasiveness. Specifically, we find that a non-native species can achieve high levels of invasiveness by possessing traits that overlap with those of its facilitators (and mutualists), which enhances the benefits accrued from positive interactions, and by possessing traits outside the range of those of antagonists, which mitigates the costs accrued from negative interactions. This ‘central-to-reap, edge-to-elude’ trait strategy therefore describes the strategic trait positions of non-native species to invade an ecological network. This model provides a theoretical platform for exploring invasion strategies in complex adaptive ecological networks.