A bifunctional enzyme with L-fucokinase and GDP-L-fucose pyrophosphorylase activities salvages free L-fucose in Arabidopsis

Monomeric sugars generated during the metabolism of polysaccharides, glycoproteins, and glycolipids are imported to the cytoplasm and converted to respective nucleotide sugars via monosaccharide 1-phosphates, to be reutilized as activated sugars. Because L-fucose (L-Fuc) is activated mainly in the form of GDP derivatives in seed plants, the salvage reactions for L-Fuc are expected to be independent from those for Glc, Gal, L-arabinose, and glucuronic acid, which are activated as UDP-sugars. For this study we have identified, in the genomic data base of Arabidopsis, the gene (designated AtFKGP) of a bifunctional enzyme with similarity to both L-fucokinase and GDP-L-Fuc pyrophosphorylase. Recombinant AtFKGP (rAt-FKGP) expressed in Escherichia coli showed both L-fucokinase and GDP-L-Fuc pyrophosphorylase activities, generating GDP-L-Fuc from L-Fuc, ATP, and GTP as the starting substrates. Point mutations in rAtFKGPs at either Gly(133) or Gly(830) caused loss of GDP-L-Fuc pyrophosphorylase and l-fucokinase activity, respectively. The apparent K(m) values of L-fucokinase activity of rAtFKGP for L-Fuc and ATP were 1.0 and 0.45 mm, respectively, and those of GDP-L-Fuc pyrophosphorylase activity for L-Fuc 1-phosphate and GTP were 0.052 and 0.17 mm, respectively. The expression of AtFKGP was detected in most cell types of Arabidopsis, indicating that salvage reactions for free L-Fuc catalyzed by AtFKGP occur ubiquitously in Arabidopsis. Loss-of-function mutants with tDNA insertion in AtFKGP exhibited higher accumulation of free L-Fuc in the soluble fraction than the wild-type plant. These results indicate that AtFKGP is a bifunctional enzyme with L-fucokinase and GDP-L-Fuc pyrophosphorylase activities, which salvages free L-Fuc in Arabidopsis.     

Molecular cloning and characterization of murine and human N-acetylglucosamine kinase.

N-Acetylglucosamine is produced by the endogenous degradation of glycoconjugates and by the degradation of dietary glycoconjugates by glycosidases. It enters the pathways of aminosugar metabolism by the action of N-acetylglucosamine kinase. In this study we report the isolation and characterization of a cDNA clone encoding the murine enzyme. An open reading frame of 1029 base pairs encodes 343 amino acids with a predicted molecular mass of 37.3 kDa. The deduced amino-acid sequence contains matches of the sequences of eight peptides derived from tryptic cleavage of rat N-acetylglucosamine kinase. The recombinant murine enzyme was functionally expressed in Escherichia coli BL21 cells, where it displays N-acetylglucosamine kinase activity as well as N-acetylmannosamine kinase activity. The complete cDNA sequence of human N-acetylglucosamine kinase was derived from the nucleotide sequences of several expressed sequence tags. An open reading frame of 1032 base pairs encodes 344 amino acids and a protein with a predicted molecular mass of 37.4 kDa. Similarities between human and murine N-acetylglucosamine kinase were 86.6% on the nucleotide level and 91.6% on the amino-acid level. Amino-acid sequences of murine and human N-acetylglucosamine kinase show sequence similarities to other sugar kinases, and all five sequence motifs necessary for the binding of ATP by sugar kinases are present. Tissue distribution of murine N-acetylglucosamine kinase revealed an ubiquitous occurrence of the enzyme and a very high expression in testis. The size of the murine mRNA was 1.35 kb in all tissues investigated, with the exception of testis, where it was 1.45 kb mRNA of the murine enzyme was continuously expressed during mouse development. mRNA of the human enzyme was expressed in all investigated human tissues, as well as in cancer cell lines. In both the tissues and the cancer cell lines, the human mRNA was 1.35 kb in size.     

Molecular cloning, chromosomal localization, and bacterial expression of a murine macrophage metalloelastase.

Murine macrophages have previously been shown to secrete a zinc-dependent proteinase that can degrade elastin. In this report, we identify murine macrophage elastase (MME) cDNA and show that it is a distinct member of the metalloproteinase gene family. Small amounts of MME were purified to homogeneity, and N-terminal amino acid sequence was obtained. This sequence was used to obtain a partial cDNA clone by the polymerase chain reaction; a cDNA library derived from a mouse macrophage-like cell line (P388D1) was screened with this probe. A full-length MME cDNA spanning approximately 1.8 kilobases contained an open reading frame of 1386 base pairs; the predicted molecular mass of the MME proenzyme is 53 kDa. The gene encoding MME is represented only once in the mouse genome and is located on chromosome 9. Despite a size that is similar to other metalloproteinases, MME is distinct, sharing only 33-48% amino acid homology with other metalloproteinases. In contrast to other metalloenzymes, MME appears to be rapidly processed to an active truncated form (N-terminal and C-terminal cleavage). We expressed recombinant MME in Escherichia coli and demonstrated that it has significant elastolytic activity that is specifically inhibited by the tissue inhibitor of metalloproteinases. MME is therefore a true metalloproteinase that may be involved in tissue injury and remodeling.     

Identification of human L-fucose kinase amino acid sequence

Fucose is a major component of complex carbohydrates. L-Fucose kinase (fucokinase) takes part in the salvage pathway for reutilization of fucose from the degradation of oligosaccharides. The amino acid sequence of human fucokinase was derived from a cDNA encoding a protein of hitherto unidentified function. Human fucokinase polypeptide chain consists of 990 amino acids with a predicted molecular mass of 107 kDa. The C-terminal part of its amino acid sequence showed sequence motifs typical for sugar kinases. Fucokinase full-length protein and a deletion mutant lacking the first 363 amino acids of the N-terminus were expressed in Escherichia coli BL21 cells. Both proteins displayed fucokinase activity. These results reveal that the discovered cDNA encodes the fucokinase protein and they confirm that a functional kinase domain is located in the C-terminal part of the enzyme.     

Cloning, sequencing, and expression of porcine interleukin-18 in Escherichia coli

IL-18 is the new name of a novel cytokine that plays an important role in T(H1) response, primarily by its ability to induce IFN-gamma production in T cells and natural killer cells. The porcine IL-18 gene was isolated using RT-PCR from porcine alveolar macrophages. Sequence analysis of the porcine IL-18 gene has demonstrated an open reading frame of 579 base pairs encoding 192 amino acids precursor protein with a predicted molecular mass of 22 kDa. The porcine IL-18 gene shares 84% and 89% similarity to the human and canine equivalents, respectively, at the nucleotide level. The cloned IL-18 was expressed in Escherichia coli and its expression was confirmed by SDS-PAGE and Western blotting.     

甘蓝型油菜小核糖核蛋白BnSmD1编码区全长cDNA 的克隆与表达分析

通过筛选野生型油菜(Pet33-10)与无花瓣油菜(Apet33-10)反向消减文库(SSH)和运用RACE-PCR技术, 获得了甘蓝型油菜小核糖核蛋白BnSmD1的全长编码区 cDNA (GenBank登陆号DQ298446)。该基因长484 bp, 含有一个长354 bp的阅读框。BnSmD1在N端拥有两个高度保守的结构域(Sm-1和Sm-2), 羧基端则含有一个RG重复序列。Northern blot表达结果显示: BnSmD1在甘蓝型油菜的各个组织均有表达, 但是它在早期花蕾中的表达明显高于同期的叶和茎。通过对BnSmD1在Apet33-10无花瓣品系与野生型有花瓣品系Pet33-10中各组织的表达差异进行比较, 发现该基因在Apet33-10的早期花蕾中表达明显下降。因此, BnSmD1可能对植物的早期花发育起到了重要的作用, 并很有可能影响花瓣的形成。     

Expression cloning of a receptor for murine granulocyte colony-stimulating factor

Two cDNAs encoding the receptor for murine granulocyte colony-stimulating factor (G-CSF) were isolated from a CDM8 expression library of mouse myeloid leukemia NFS-60 cells, and their nucleotide sequences were determined. Murine G-CSF receptor expressed in COS cells could bind G-CSF with an affinity and specificity similar to that of the native receptor expressed by mouse NFS-60 cells. The amino acid sequence encoded by the cDNAs has demonstrated that murine G-CSF receptor is an 812 amino acid polypeptide (Mr, 90,814) with a single transmembrane domain. The extracellular domain consists of 601 amino acids with a region of 220 amino acids that shows a remarkable similarity to rat prolactin receptor. The cytoplasmic domain of the G-CSF receptor shows a significant similarity with parts of the cytoplasmic domain of murine interleukin-4 receptor. A 3.7 kb mRNA coding for the G-CSF receptor could be detected in mouse myeloid leukemia NFS-60 and WEHI-3B D+ cells as well as in bone marrow cells.     

Mouse cathepsin F: cDNA cloning, genomic organization and chromosomal assignment of the gene

A murine cysteine protease of the papain family was identified by dbEST-database search. A 1.87kb full-length cDNA encoding a predicted polypeptide of 462 amino acids was sequenced. Since the encoded polypeptide shows more than 80% sequence identity with human cathepsin F, it is most likely that this cDNA represents the murine homologue of cathepsin F, and it was therefore named accordingly. Murine cathepsin F exhibits a domain structure typical for papain-like cysteine proteases, a 20 amino acid N-terminal hydrophobic signal sequence followed by an extraordinarily long propeptide of 228 amino acids and the domain of the mature protease comprising 214 amino acids. The mature region contains all features characteristic of a papain-like cysteine protease, including the highly conserved cysteine, histidine and asparagine residues of the 'catalytic triad'. Genomic clones covering the murine cathepsin F gene were isolated. The mouse cathepsin F gene consists of 14 exons and 13 introns and spans 5.8kb. Murine cathepsin F was mapped to chromosome 19, a region with synteny homology to a region of human chromosome 11 to which human cathepsin F has been mapped previously. Northern blot analysis of RNA from multiple tissues revealed a ubiquitous expression of cathepsin F in mouse and man.     

The complete nucleotide sequence of murine beta-glucuronidase mRNA and its deduced polypeptide

The complete nucleotide sequence of murine beta-glucuronidase (GUS) mRNA has been compiled from three overlapping cloned cDNAs and a single GUS-specific genomic clone. The sequence is composed of 2455 nucleotides, exclusive of the poly(A) tail. The 5' and 3' untranslated regions contain 12 and 499 bases, respectively, with the open reading frame encoding a polypeptide of 648 amino acids (74.2 kDa), including a 22 amino acid signal sequence. The nucleotide and deduced amino acid sequences of murine GUS are compared to those published for rat and human GUS and the results are presented. Murine GUS also shares amino acid sequence identity with Escherichia coli GUS and beta-galactosidase. The complete sequences of murine GUS mRNA and its deduced polypeptide provide a basis from which to study the mechanisms responsible for the well-characterized variation in GUS expression among inbred mouse strains.     

Molecular and Biochemical Characterization of Rat epsilon -N-Trimethyllysine Hydroxylase, the First Enzyme of Carnitine Biosynthesis.

epsilon-N-Trimethyllysine hydroxylase (EC ) is the first enzyme in the biosynthetic pathway of l-carnitine and catalyzes the formation of beta-hydroxy-N-epsilon-trimethyllysine from epsilon-N-trimethyllysine, a reaction dependent on alpha-ketoglutarate, Fe(2+), and oxygen. We purified the enzyme from rat kidney and sequenced two internal peptides by quadrupole-time-of-flight mass spectroscopy. The peptide sequences were used to search the Expressed Sequence Tag data base, which led to the identification of a rat cDNA of 1218 base pairs encoding a polypeptide of 405 amino acids with a calculated molecular mass of 47.5 kDa. Using the rat sequence we also identified the homologous cDNAs from human and mouse. Heterologous expression of both the rat and human cDNAs in COS cells confirmed that they encode epsilon-N-trimethyllysine hydroxylase. Subcellular fractionation studies revealed that the rat enzyme is localized exclusively in mitochondria. Expression studies in yeast indicated that the rat enzyme is synthesized as a 47.5-kDa precursor and subsequently processed to a mature protein of 43 kDa, presumably upon import in mitochondria. The Michaelis-Menten constants of the purified rat enzyme for trimethyllysine, alpha-ketoglutarate, and Fe(2+) were 1.1 mm, 109 microm, and 54 microm, respectively. Both gel filtration and blue native polyacrylamide gel electrophoresis analysis showed that the native enzyme has a mass of approximately 87 kDa, indicating that in rat epsilon-N-trimethyllysine hydroxylase is a homodimer.     

Molecular cloning of the cDNA encoding a murine sialic acid-specific 9-O-acetylesterase and RNA expression in cells of hematopoietic and non-hematopoietic origin.

We describe the isolation of a cDNA encoding a murine sialic acid-specific 9-O-acetylesterase as well as its expression pattern in cells of both hematopoietic and non-hematopoietic origin. This enzyme catalyzes the removal of O-acetyl ester groups from position 9 of the parent sialic acid N-acetylneuraminic acid. The cDNA is 2105 nt in length and encodes a protein of 541 amino acids with a predicted molecular weight of 61 kDa, not including oligosaccharides linked to eight potential N-glycosylation sites. The cDNA encoding the acetylesterase displays a widespread distribution in various cell lines and tissues. Expression studies of B lineage cell lines and primary fetal liver cells revealed a developmentally regulated expression pattern in cells of hematopoietic origin. Given the importance of 9-O-acetylation of sialic acids, the cloning of the cDNA encoding a sialic acid-specific 9-O-acetylesterase will be helpful in understanding further the regulation of this post-translational modification and the biological consequences thereof.     

Molecular cloning and expression of the murine interleukin-5 receptor

Murine interleukin-5 (IL-5) is known to play an essential role in Ig production of B cells and proliferation and differentiation of eosinophils. Here, we have isolated cDNA clones encoding a murine IL-5 receptor by expression screening of a library prepared from a murine IL-5 dependent early B cell line. A cDNA library was expressed in COS7 cells and screened by panning with the use of anti-IL-5 receptor monoclonal antibodies. The deduced amino acid sequence analysis demonstrates that the receptor is a glycoprotein of 415 amino acids (Mr 45,284), including an N-terminal hydrophobic region (17 amino acids), a glycosylated extracellular domain (322 amino acids), a single transmembrane segment (22 amino acids) and a cytoplasmic tail (54 amino acids). COS7 cells transfected with the cDNA expressed a 60 kd protein that bound IL-5 with a single class of affinity (KD = 2-10 nM). FDC-P1 cells transfected with the cDNA for murine IL-5 receptor showed the expression of IL-5 binding sites with both low (KD = 6 nM) and high affinity (KD = 30 pM) and acquired responsiveness to IL-5 for proliferation, although parental FDC-P1 cells did not show any detectable IL-5 binding. In addition, several cDNA clones encoding soluble forms of the IL-5 receptor were isolated. Northern blot analysis showed that two species of mRNAs (5.0 kb and 5.8 kb) were detected in cell lines that display binding sites for murine IL-5. Homology search for the amino acid sequence of the IL-5 receptor reveals that the IL-5 receptor contains a common motif of a cytokine receptor family that is recently identified.