Tyrosine sulphation is not required for microvillar expression of intestinal aminopeptidase N.
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ABSTRACT:
SUBMITTER: Danielsen EM
PROVIDER: S-EPMC1135059 | biostudies-other | 1988 Aug
REPOSITORIES: biostudies-other
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Project description:The biosynthesis of small-intestinal aminopeptidase N (EC 3.4.11.2) was studied in a cell-free translation system derived from rabbit reticulocytes. When dog pancreatic microsomal fractions were present during translation, most of the aminopeptidase N synthesized was found in a membrane-bound rather than a soluble form, indicating that synthesis of the enzyme takes place on ribosomes attached to the rough endoplasmic reticulum. The microsomal fractions process the Mr-115 000 polypeptide, which is the primary translation product of aminopeptidase N, to a polypeptide of Mr 140 000. This was found to be sensitive to the action of endo-beta-N-acetylglucosaminidase H (EC 3.2.1.96), showing that aminopeptidase N undergoes transmembrane glycosylation during synthesis. The position of the signal sequence in aminopeptidase N was determined by a synchronized translation experiment. It was found that microsomal fractions should be added before about 25% of the polypeptide was synthesized to ensure processing to the high-mannose glycosylated form. This suggests that the signal sequence is situated in the N-terminal part of the aminopeptidase N. The size of the cell-free translation product in the absence of microsomal fractions was found to be similar to that on one of the forms of the enzyme obtained from tunicamycin-treated organ-cultured intestinal explants.
| S-EPMC1152024 | biostudies-other
Project description:The biogenesis of two microvillar enzymes, aminopeptidase N (EC 3.4.11.2) and sucrase (EC 3.2.1.48)-isomaltase (EC 3.2.1.10), was studied by pulse-chase labelling of pig small-intestinal explants kept in organ culture. Both enzymes became inserted into the membrane during or immediately after polypeptide synthesis, indicating that translation takes place on ribosomes attached to the rough endoplasmic reticulum. The earliest detectable forms of aminopeptidase and sucrase-isomaltase were polypeptides of Mr 140 000 and 240 000 respectively. These polypeptides were susceptible to treatment with endo-beta-N-acetylglucosaminidiase H (EC 3.2.1.96), suggesting that the microvillar enzymes during or immediately after completion of protein synthesis become glycosylated with a 'high-mannose' oligosaccharide structure similarly to other plasma-membrane and secretory proteins. After 20--40 min or 60--90 min of chase, respectively, aminopeptidase N and sucrase-isomaltase were reglycosylated to give the polypeptides of Mr 166 000 (aminopeptidase N) and 265 000 (sucrase-isomaltase). These were expressed at the microvillar membrane after 60--90 min. During the entire process of synthesis and transport to the microvillar membrane the enzymes were bound to membranes, indicating that the biogenesis of aminopeptidase N and sucrase-isomaltase occurs in accordance with the membrane flow hypothesis.
| S-EPMC1158402 | biostudies-other
Project description:Castanospermine, an inhibitor of glucosidase I, the initial enzyme in the trimming of N-linked carbohydrate, was used to study the importance of carbohydrate processing in the biosynthesis of microvillar enzymes in organ-cultured pig intestinal explants. For aminopeptidase N (EC 3.4.11.2), aminopeptidase A (EC 3.4.11.7), sucrase-isomaltase (EC 3.2.1.48-10) and maltase-glucoamylase (EC 3.2.1.20), castanospermine caused the formation of novel transient forms of higher Mr than corresponding controls, indicating a blocked removal of glucose residues. For the first three enzymes, the 'mature' (Golgi-processed) forms were similar in size to or slightly smaller than corresponding controls and were, as shown for aminopeptidase N, endoglycosidase-H-sensitive, evidence of a blocked attachment of complex sugars. Maltase-glucoamylase did not undergo conversion into a 'mature' form, suggesting that, unlike other microvillar enzymes, it does not receive post-translational O-linked carbohydrate. Castanospermine suppressed the synthesis of the four enzymes, but did not block their transport to the microvillar membrane, showing that processing of N-linked carbohydrate is not required for microvillar expression. The proteinase inhibitor leupeptin partially restored the suppressed synthesis, indicating that the majority of the wrongly processed enzymes, probably because of conformational instability, become degraded soon after synthesis rather than being transported to the microvillar membrane.
| S-EPMC1147486 | biostudies-other
Project description:The post-translational processing of pig small-intestinal aminopeptidase N (EC 3.4.11.2) was studied in organ-cultured mucosal explants. Exposure of the explants to swainsonine, an inhibitor of Golgi mannosidase II, resulted in the formation of a Mr-160000 polypeptide, still sensitive to endo-beta-N-acetylglucosaminidase H. Swainsonine caused only a moderate inhibition of transport of the enzyme through the Golgi complex and the subsequent expression in the microvillar membrane. This may imply that the trimming of the high-mannose core and complex glycosylation of N-linked oligosaccharides is not essential for the transport of aminopeptidase N to its final destination. A different type of processing was observed to take place in the presence of swainsonine, resulting in a considerable increase in apparent Mr (from 140000 to 160000). This processing could not be ascribed to N-linked glycosylation, since treatment of the Mr-160000 polypeptide with endo-beta-N-acetylglucosaminidase H only decreased its apparent Mr by 15000. The susceptibility of the mature Mr-166000 polypeptide, but not the Mr-140000 polypeptide, to mild alkaline hydrolysis suggests that aminopeptidase N becomes glycosylated with O-linked oligosaccharides during its passage through the Golgi complex. Aminopeptidase N was not labelled by [3H]palmitic acid, indicating that the processing of the enzyme does not include acylation.
| S-EPMC1152508 | biostudies-other
Project description:The biogenesis of three intestinal microvillar enzymes, maltase-glucoamylase (EC 3.2.1.20), aminopeptidase A (aspartate aminopeptidase, EC 3.4.11.7) and dipeptidyl peptidase IV (EC 3.4.14.5), was studied by pulse-chase labelling of pig small-intestinal explants kept in organ culture. The earliest detectable forms of the enzymes were polypeptides of Mr 225000, 140000 and 115000 respectively. These were found to represent the enzymes in a 'high-mannose' state of glycosylation, as judged by their susceptibility to treatment with endo-beta-N-acetylglucosaminidase H (EC 3.2.1.96). After about 40-60 min of chase, maltase-glucoamylase, aminopeptidase A and dipeptidyl peptidase IV were further modified to yield the mature polypeptides of Mr 245000, 170000 and 137000 respectively, which were expressed at the microvillar membrane after 60-90 min of chase. The fact that the enzymes before reaching the microvillar membrane were found in a Ca2+-precipitated membrane fraction (intracellular and basolateral membranes), but not in soluble form, indicates that during biogenesis maltase-glucoamylase, aminopeptidase A and dipeptidyl peptidase IV are transported and assembled in a membrane-bound state.
| S-EPMC1154236 | biostudies-other
Project description:A crude RNA fraction, prepared from pig small intestine, was found to be more efficient than a fraction enriched in polyadenylated RNA in directing translation of polypeptides with Mr greater than 100000 in a rabbit reticulocyte lysate system. Aminopeptidase N (EC 3.4.11.2) synthesized in vitro was immunopurified from the translation mixture and analysed by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. It was found to have an apparent Mr of 115000 regardless of whether the translation was performed in the absence or presence of proteinase inhibitors. This result contradicts the possibility of aminopeptidase N being synthesized as a large single-chain precursor polypeptide.
| S-EPMC1158348 | biostudies-other
Project description:Porcine deltacoronavirus (PDCoV) is an economically important enteropathogen of swine with worldwide distribution. PDCoV primarily infects the small intestine instead of the large intestine in vivo However, the underlying mechanism of PDCoV tropism to different intestinal segments remains poorly understood as a result of the lack of a suitable in vitro intestinal model that recapitulates the cellular diversity and complex functions of the gastrointestinal tract. Here, we established the PDCoV infection model of crypt-derived enteroids from different intestinal segments. Enteroids were susceptible to PDCoV, and multiple types of different functional intestinal epithelia were infected by PDCoV in vitro and in vivo We further found that PDCoV favorably infected the jejunum and ileum and restrictedly replicated in the duodenum and colon. Mechanistically, enteroids from different intestinal regions displayed a distinct gene expression profile, and the differential expression of primary viral receptor host aminopeptidase N (APN) instead of the interferon (IFN) responses determined the susceptibility of different intestinal segments to PDCoV, although PDCoV substantially elicited antiviral genes production in enteroids after infection. Additional studies showed that PDCoV infection significantly induced the expression of type I and III IFNs at the late stage of infection, and exogenous IFN inhibited PDCoV replication in enteroids. Hence, our results provide critical inputs to further dissect the molecular mechanisms of PDCoV-host interactions and pathogenesis.IMPORTANCE The zoonotic potential of the PDCoV, a coronavirus efficiently infecting cells from a broad range species, including porcine, chicken, and human, emphasizes the urgent need to further study the cell and tissue tropism of PDCoV in its natural host. Herein, we generated crypt stem cell-derived enteroids from porcine different intestinal regions, which well recapitulated the events in vivo of PDCoV infection that PDCoV targeted multiple types of intestinal epithelia and preferably infected the jejunum and ileum over the duodenum and colon. Mechanistically, we demonstrated that the expression of APN receptor rather than the IFN responses determined the susceptibility of different regions of the intestines to PDCoV infection, though PDCoV infection markedly elicited the IFN responses. Our findings provide important insights into how the distinct gene expression profiles of the intestinal segments determine the cell and tissue tropism of PDCoV.
| S-EPMC7343211 | biostudies-literature
Project description:The rates of biosynthesis of adult and foetal pig small-intestinal aminopeptidase N (EC 3.4.11.2) were compared to determine at which level the expression of the microvillar enzyme is developmentally controlled. In organ-cultured explants, the rate of biosynthesis of foetal aminopeptidase N is only about 3% of the adult rate. The small amount synthesized occurs in a high-mannose-glycosylated, membrane-bound, form that is processed to the mature, complex-glycosylated, form at a markedly slower rate than that of the adult enzyme. Extracts of total RNA from adult and foetal intestine contained comparable amounts of aminopeptidase N mRNA, encoding gel-electrophoretically identical primary translation products. Together, these data indicate that the expression of aminopeptidase N is controlled at a translational level.
| S-EPMC1146707 | biostudies-other
Project description:Aminopeptidase W is a newly discovered enzyme of the renal and intestinal brush borders, having been first isolated as a 130 kDa glycoprotein recognized by a monoclonal antibody [Gee & Kenny (1985) Biochem. J. 230, 753-764]. It is particularly effective in the hydrolysis of dipeptides, Glu-Trp (Km 0.57 mM; kcat. 6770 min-1) being a favoured substrate. Dipeptides with tryptophan, phenylalanine or tyrosine in the P1 position were rapidly hydrolysed, but the requirements in respect of the P1 residue were not stringent. The activity of aminopeptidase W is markedly influenced by ionic conditions. The highest activity was observed in 100 mM-Tris/HCl, pH 8; phosphate ions were strongly inhibitory. Activity was also greatly affected by bivalent metal ions, and the magnitude and direction of the effects depended on the nature of the buffer anions and on pH. The most effective inhibitors were amastatin and bestatin. Some thiols also inhibited, but other chelating agents, EDTA and 1,10-phenanthroline, had no effect over the concentration range 1-10 mM. Other group-specific inhibitors, for cysteine, serine or aspartic peptidases, were also ineffective. Some molecular properties were studied. Deglycosylation by treatment with N-glycanase diminished the apparent subunit Mr from 130,000 to 90,000. The enzyme contained zinc, 1.2 atoms/subunit, and in spite of the atypical properties of this enzyme in respect of chelating agents, a zinc-catalysed mechanism is the most probable. Its roles in digestion and in renal function are not yet clear.
| S-EPMC1148244 | biostudies-other
Project description:In a chemical screening, we tested the antiangiogenic effects of fumagillin derivatives and identified fumagillin as an inhibitor of definitive hematopoiesis in zebrafish embryos. Fumagillin is known to target methionine aminopeptidase II (MetAP2), an enzyme whose function in hematopoiesis is unknown. We investigated the role of MetAP2 in hematopoiesis by using zebrafish embryo and human umbilical cord blood models. Zebrafish metap2 was expressed ubiquitously during early embryogenesis and later in the somitic region, the caudal hematopoietic tissue, and pronephric duct. metap2 was inhibited by morpholino and fumagillin treatment, resulting in increased mpo expression at 18 hours postfertilization and reduced c-myb expression along the ventral wall of dorsal aorta at 36 hours postfertilization. It also disrupted intersegmental vessels in Tg(fli1:gfp) embryos without affecting development of major axial vasculatures. Inhibition of MetAP2 in CB CD34(+) cells by fumagillin had no effect on overall clonogenic activity but significantly reduced their engraftment into immunodeficient nonobese diabetes/severe combined immunodeficiency mice. metap2 knock-down in zebrafish and inhibition by fumagillin in zebrafish and human CB CD34(+) cells inhibited Calmodulin Kinase II activity and induced ERK phosphorylation. This study demonstrated a hitherto-undescribed role of MetAP2 in definitive hematopoiesis and a possible link to noncanonical Wnt and ERK signaling.
| S-EPMC3342862 | biostudies-literature