Identification of glutamic acid decarboxylase autoantibody heterogeneity and epitope regions in type I diabetes

Glutamic acid decarboxylase (GAD) is an autoantigen of the islet cell antibodies (ICAs) present in type I diabetes. GAD autoantibodies are also found in patients with stiffman syndrome and in certain ICA-positive individuals who rarely develop diabetes on long-term follow-up. This latter subset of ICA has been termed restricted or beta-cell-specific ICA because the antibodies react with only the beta-cells of the islet. By immunoprecipitation of recombinant GAD65 and GAD67 protein and protein fragments, 83% of sera from individuals with new-onset diabetes or prediabetes (n = 30) had GAD65 autoantibodies, but only 26% had GAD67 autoantibodies. In contrast, all restricted ICA sera (n = 6) had both GAD65 and GAD67 autoantibodies. In both types of sera, the binding of GAD67 autoantibodies could be blocked by preincubation of the serum with GAD65 and GAD67, but the binding of GAD65 autoantibodies could not be blocked by preincubation with GAD67. The titer of GAD65 autoantibodies was much higher in the restricted ICA sera (titer > 1:1,000) than in the sera from individuals with new-onset diabetes or prediabetes (titer < 1:100) and was reflected by the greater amount of GAD65 protein immunoprecipitated by restricted ICA sera (2.61 +/- 1.39 U) compared with sera from individuals with new-onset diabetes (0.51 +/- 0.34 U). The restricted ICA sera immunoprecipitated equimolar amounts of GAD65 protein fragments, suggesting a non-conformational or linear epitope; epitope mapping localized the major epitope region to amino acids 361-442 and a second minor epitope region to amino acids 1-195.(ABSTRACT TRUNCATED AT 250 WORDS)

A novel radioligand binding assay to determine diagnostic accuracy of isoform-specific glutamic acid decarboxylase antibodies in childhood IDDM

Insulin-dependent diabetes mellitus (IDDM) is associated with autoreactivity against GAD but the diagnostic sensitivity (positivity in disease) and specificity (negativity in health) of isoform-specific GAD antibodies have yet to be defined in assay systems suitable for screening large number of samples. One set of IDDM patient (n = 10) and control (n = 50) standard sera were used to develop quantitative antibody assays with in vitro synthesized recombinant 35S-methionine-labelled GAD65 and GAD67, respectively, and protein A-Sepharose to separate free from antibody-bound ligand. Binding levels were not normally distributed (p < 0.0001) and therefore, the diagnostic accuracy of GAD antibodies was analysed by the ROC plots in population-based, consecutively-diagnosed, recent onset, 0-14 year-old patients (n = 105), and matched, healthy control subjects (n = 157). The ROC plots showed that the diagnostic sensitivity of GAD65 antibodies was 77% and the specificity 92% compared with 8% and 98%, respectively for GAD67 antibodies. In the IDDM sera, GAD65 and GAD67 antibodies were concordant in 7% (6 of 81) and GAD65 antibodies and ICA in 89% (72 of 81) without a correlation between the autoantibody levels. Autoantibodies to recombinant human islet GAD65 are specific and sensitive markers for childhood IDDM in this immunoassay with in vitro synthesized 35S-methionine-labelled recombinant GAD.

Structure-function relationships in naturally occurring mutants of pancreatic lipase

From primary structure comparison, the pancreatic lipase family is now divided into three subgroups: classical pancreatic lipases, pancreatic lipase-related proteins 1 (RPI) and pancreatic lipase-related proteins 2 (RP2). Among the RP2 subfamily, the guinea-pig and coypu enzymes share kinetic properties which differ from those of classical pancreatic lipases. Both enzymes display a high phospholipase activity and are not interfacially activated using a short chain triglyceride as substrate. Their activity towards insoluble triglycerides is inhibited by micellar concentrations of bile salts and is not restored by addition of colipase. These atypical kinetic properties are discussed in the light of amino acid sequence comparison between RP2 and classical pancreatic lipases, based on the closed and open conformations of the 3-D structure of human pancreatic lipase.

Actions of phenylglycine analogs at subtypes of the metabotropic glutamate receptor family

The functional effects of phenylglycine analogs on metabotropic glutamate receptor (mGluR) subtypes mGluR1 alpha, mGluR2 and mGluR4 were examined. (S)-4-Carboxyphenylglycine (IC50 = 65 +/- 5 microM), (R,S)-alpha-methyl-4-carboxyphenylglycine (IC50 = 155 +/- 38 microM) and (S)-3-carboxy-4-hydroxyphenylglycine (IC50 = 290 +/- 47 microM) competitively antagonized glutamate-stimulated phosphoinositide hydrolysis in baby hamster kidney (BHK) cells stably expressing mGluR1 alpha. (S)-4-Carboxyphenylglycine and (R,S)-alpha-methyl-4-carboxyphenylglycine competitively antagonized glutamate-induced inhibition of forskolin-stimulated cAMP-formation in BHK cells stably expressing mGluR2 with IC50 values of 577 +/- 74 microM and 340 +/- 59 microM, respectively. (R,S)-4-carboxy-3-hydroxyphenylglycine, (R)-3-hydroxyphenylglycine and (S)-3-carboxy-4-hydroxyphenylglycine were agonists at mGluR2 with EC50 values of 48 +/- 5 microM, 451 +/- 93 and 97 +/- 12 microM, respectively. In parallel experiments, no activities of these phenylglycine analogs at mGluR4 were observed. The present report demonstrates that phenylglycine analogs possess differential functional activities at subtypes of the mGluR family.

Detection of GAD65 antibodies in diabetes and other autoimmune diseases using a simple radioligand assay

Autoantibodies to glutamic acid decarboxylase (GAD) are frequent at or before the onset of insulin-dependent diabetes mellitus (IDDM). We have developed a simple, reproducible, and quantitative immunoprecipitation radioligand assay using as antigen in vitro transcribed and translated [35S]methionine-labeled human islet GAD65. By using this assay, 77% (77 of 100) of serum samples from recent-onset IDDM patients were positive for GAD65 antibodies compared with 4% (4 of 100) of serum samples from healthy control subjects. In competition analysis with unlabeled purified recombinant human islet GAD65, binding to tracer was inhibited in 74% (74 of 100) of the GAD65-positive IDDM serum samples compared with 2% of the control samples. The levels of GAD antibodies expressed as an index value relative to a standard serum, analyzed with or without competition, were almost identical (r = 0.991). The intra- and interassay variations of a positive control serum sample were 2.9 and 7.6%, respectively (n = 4). The frequency of GAD antibodies was significantly higher with IDDM onset before the age of 30 (80%, 59 of 74) than after the age of 30 (48%, 10 of 21) (P < 0.01). The prevalence of islet cell antibodies showed a similar pattern relative to age at onset. Because simultaneous occurrences of multiple autoimmune phenomena are common, we analyzed sera from patients with other autoimmune diseases. The frequency of GAD antibodies in sera positive for DNA autoantibodies (8% [2 of 25] and 4% [1 of 25] in competition analysis) or rheuma factor autoantibodies [12% (4 of 35) and 3% (1 of 35) in competition analysis] was not different from that in control samples. In contrast, in sera positive for ribonucleoprotein antibodies the frequency of GAD antibodies was significantly increased (73% [51 of 70] and 10% [7 of 70] in competition analysis [P < 0.025]). In conclusion, even large numbers of serum samples can now be tested for GAD65 antibodies in a relatively short time, allowing screening of individuals without a family history of IDDM for the presence of this marker.

Thiol ester role in correct folding and conformation of human alpha 2-macroglobulin. Properties of recombinant C949S variant

To determine the role of the thiol ester in the folding of human alpha 2-macroglobulin (alpha 2M) in the active conformation, we have characterized a recombinant variant of alpha 2M, C949S, expressed in baby hamster kidney cells, that lacks the thiol ester-forming cysteine. C949S alpha 2M behaves like methylamine-treated plasma alpha 2M, with correctly formed inter-subunit disulfide bridges, non-covalent association of covalent dimers to form tetramers, and exposure of the receptor binding domain, but an inability to inhibit proteinases, and inaccessibility of the bait regions to proteolysis. We concluded that correct folding of monomers or their association to give tetrameric alpha 2M does not require a pre-formed thiol ester. Active alpha 2M may form in vivo by a two-step process involving initial folding to give a structure resembling that of C949S alpha 2M followed by thiol ester formation and a conformational change that gives the native active state.

Cloning of the classical guinea pig pancreatic lipase and comparison with the lipase related protein 2

Starting from total pancreatic mRNAs, the classical guinea pig pancreatic lipase was cloned using rapid amplification of 3' and 5' cDNA ends. Internal oligonucleotide primers were designed from a partial cDNA clone including the region coding for the lid domain. Using this strategy, we did not amplify the cDNA corresponding to the pancreatic lipase related protein 2 in which the lid domain is deleted. Amino acid sequences of the classical guinea pig pancreatic lipase and the related protein 2 were compared based on the primary and tertiary structures of the classical human pancreatic lipase. Their distinct physiological roles are discussed in the light of functional amino acid differences.

Human G(olf) alpha: complementary deoxyribonucleic acid structure and expression in pancreatic islets and other tissues outside the olfactory neuroepithelium and central nervous system

G(olf) alpha is a G-protein originally believed to mediate signal transduction exclusively within the olfactory neuroepithelium and subsequently found to be a major stimulatory G-protein in the basal ganglia. Here we present evidence that G(olf) alpha is expressed in several other tissues. The human isoform of G(olf) alpha was isolated from two human insulinoma cDNA libraries. Comparison of the human sequence with rat G(olf) alpha shows 91% nucleotide identity (within the coding region) and 99% identity at the amino acid level. Northern and reverse transcriptase-polymerase chain reaction analyses indicated that G(olf) alpha is expressed in all human insulinomas examined thus far as well as in normal pancreatic islets. G(olf) alpha mRNA was also detected in testis, retina, brain, and liver. Western blot analysis of various mouse tissues demonstrated that the level of G(olf) alpha protein in islets is lower than that in the olfactory neuroepithelium and other parts of the brain; its expression in retina, lung, and spleen was moderately higher than that in islets, and its expression in testis approached that in olfactory neuroepithelium. G(olf) alpha was also detected by immunohistochemistry in mouse islets, human insulinomas, the epithelial lining of mouse epididymis, photoreceptor cells of mouse retina, and mouse lung alveoli. These findings suggest a role for G(olf) alpha in a diverse population of cells located outside the olfactory neuroepithelium and central nervous system.

A zinc-finger gene ZNF141 mapping at 4p16.3/D4S90 is a candidate gene for the Wolf-Hirschhorn (4p-) syndrome

Chromosomal aneusomy is a major cause of reproductive wastage and congenital malformations in man. Zinc finger encoding genes would be good candidates for being involved in the multiple developmental defects associated with chromosomal aneusomy--by virtue of their role as transcriptional regulators, their abundance in the genome and their known association with specific developmental disorders. We have isolated and mapped a zinc finger encoding cDNA (ZNF141) of the C2-H2/KRAB subfamily to the 4p- (Wolf-Hirschhorn) syndrome (WHS) chromosome region. ZNF141 mapped to the distal end of the 2.2 Mb smallest region of deletion overlap of WHS, 300 kb from the 4p telomere on cosmid CD1 defining the anonymous locus D4S90. ZNF141 was expressed ubiquitously at low levels in the analysed tissue. The identification of a candidate gene for a chromosomal aneusomy syndrome belonging to a class of evolutionary conserved genes will provide options for studying its normal and abnormal expression during mammalian embryogenesis.

A structural domain (the lid) found in pancreatic lipases is absent in the guinea pig (phospho)lipase

Typically pancreatic lipases are characterized by the following properties: (1) they are activated by lipid/water interfaces (interfacial activation), (2) they are inhibited by bile salts but reactivated by colipase (a small activator protein), and (3) they do not hydrolyze significantly phospholipids. A cDNA clone encoding a guinea pig pancreatic (phospho)lipase (GPL) has been sequenced and expressed. The enzyme (recombinant as well as native) differs from other pancreatic lipases in that (1) it is not interfacially activated, (2) its activity is unaffected by the presence of bile salts and/or colipase using tributyrin as substrate, and (3) it exhibits equally phospholipase A1 and lipase activities. The amino acid sequence of GPL is highly homologous to that of other known pancreatic lipases, with the exception of a deletion in the so-called lid domain that regulates access to the active centers of other lipases. We propose that this deletion is directly responsible for the anomalous behavior of this enzyme. Thus GPL challenges the classical distinction between lipases, esterases, and phospholipases.

Differential expression of glutamic acid decarboxylase in rat and human islets

The GABA synthesizing enzyme GAD is a prominent islet cell autoantigen in type I diabetes. The two forms of GAD (GAD64 and GAD67) are encoded by different genes in both rats and humans. By in situ hybridization analysis of rat and human pancreases, expression of both genes was detected in rat islets, whereas only GAD64 mRNA was detected in human islets. Immunocytochemical analysis of rat and human pancreatic sections or isolated islets with antibodies to GAD64 and GAD67 in combination with antibodies to insulin, glucagon, or SRIF confirmed that a GAD64 and GAD67 expression were beta-cell specific in rat islets. In contrast, only GAD64 was detected in human islets and was, in addition to beta-cells, also surprisingly localized to some alpha-cells, delta-cells, and PP-cells. In long-term (4 wk) monolayer cultures of newborn rat islet cells, GAD64 expression remained beta-cell specific as observed in vivo, whereas GAD67 was localized not only to the beta-cells but also in the alpha-cells and delta-cells. A small but distinct fraction of GAD positive cells in these monolayer cultures did not accumulate GABA immunoreactivity, which may indicate cellular heterogeneity with respect to GABA catabolism or GAD enzyme activity. In a rat insulinoma cell line (NHI-6F) producing both glucagon and insulin depending on the culture conditions, GAD64 expression was detected only in cultures in which the insulin producing phenotype dominated. In conclusion, these data demonstrate that the two GAD isoforms are differentially expressed in rat and human islets but also that the expression differs according to culture conditions. These findings emphasize the need to consider both the species and culture conditions of islets.

Quantitative assay using recombinant human islet glutamic acid decarboxylase (GAD65) shows that 64K autoantibody positivity at onset predicts diabetes type

At and before onset, most insulin-dependent diabetics (IDDM) have islet GAD65 autoantibodies (GAD65Ab). Since IDDM also occurs in older patients where non-insulin-dependent diabetes is common, we studied GAD65Ab at onset to classify diabetes type. Our quantitative immunoprecipitation assay uses recombinant human islet GAD65 stably expressed in hamster fibroblasts. Electrophoretic mobility was identical to native islet GAD65. Like native antigen, recombinant GAD65 migrated as two bands during electrophoresis, but converted to one under stronger reduction. Immunoprecipitation was linear with respect to antibody or antigen concentration. In 120 population-based diabetic patients of all ages grouped by treatment at onset and after 18 mo, GAD65Ab were present in 70% on insulin (n = 37), 10% on oral agent (n = 62, P < 0.0001), 69% changing from oral agent to insulin (n = 16, P < 0.001), and 1 of 33 controls. 65% with GAD65Ab, versus 8% without, changed from oral agent to insulin (P < 0.01). The GAD65Ab quantitative index was remarkably stable, and only 2 of 32 patients changed antibody status during follow-up. Concordance between GAD65Ab and islet cell antibodies was 93%. Quantitative correlation was approximate but significant. This highly sensitive, quantitative, high capacity assay for GAD65Ab reveals treatment requirements better than clinical criteria, perhaps guiding immunomodulatory therapy.

The nucleotide sequence of the variable region in Trypanosoma brucei completes the sequence analysis of the maxicircle component of mitochondrial kinetoplast DNA

The nucleotide sequence of two non-contiguous DNA fragments of 4.0 and 2.2 kb, respectively, of the kinetoplast maxicircle of Trypanosoma brucei brucei EATRO strain 427 has been determined, completing the sequence analysis of the so-called variable region (see also de Vries et al., 1988, Mol. Biochem. Parasitol. 27, 71-82). Analysis of the entire 8-kb variable region sequence revealed the presence of a 5.2-kb cluster of imperfect, tandemly repeated sequences, flanked by DNA of unique sequence. Both repetitive and unique DNA evolve rapidly, but comparison to the closely related strain EATRO 164 indicated that the repetitive cluster is more prone to sequence and size divergence. The variable region is transcribed into RNAs of varying lengths but appears to be devoid of genes encoding mitochondrial proteins or tRNAs, as judged from computer analysis. Moreover, genes that could encode guide RNAs involved in producing the known edited mitochondrial mRNA sequences are also absent. The repetitive DNA cluster within this region consists of 14 blocks each containing one 130 bp repeat and a variable number of 19 bp repeats. A duplicated sequence was identified (5'-GGGGTTGGTGT) which proved to be identical to the eleven 5'-terminal residues of the universal minicircle dodecamer involved in initiation of leading strand synthesis. This suggests a role for these sequences in the initiation of maxicircle DNA replication. With the data presented in this report, the nucleotide sequence analysis of the 23016 bp maxicircle of T. brucei brucei EATRO strain 427 has been completed.

Recombinant glutamic acid decarboxylase (representing the single isoform expressed in human islets) detects IDDM-associated 64,000-M(r) autoantibodies

GAD is an autoantigen in IDDM. Molecular cloning and specific antibodies allowed us to demonstrate that only the lower M(r) GAD64 isoform is expressed in human islets, in contrast to human brain, rat islets, and rat brain, all of which express both GAD64 and GAD67. Expression of the human islet GAD64 isoform in COS-7 and BHK cells resulted in an enzymatically active rGAD64, which is immunoreactive with diabetic sera comparable with that of the islet 64,000-M(r) autoantigen. Immunoprecipitation analyses showed that 21/28 (75%) IDDM sera had rGA D64 antibodies compared with only 1/59 (1.7%) of the healthy control sera. In immunoblot analyses, an SMS serum--but only 1/10 randomly selected IDDM sera--recognized the blotted rGAD64 without relation to immunoprecipitation titers. In conclusion, only the GA D64 isoform is expressed in human islets, in contrast to rat islets, which also express the GAD67 isoform. The immunological properties of human rGAD64 are comparable with the native 64,000-M(r) islet autoantigen, allowing further studies of the immunopathogenesis of IDDM.

Establishment of two continuous T-cell strains from a single plaque of a patient with mycosis fungoides

From a plaque biopsy of a patient with mycosis fungoides, two different continuous cell lines were established by including both IL-2 and IL-4 in the culture medium. Both continuous cell lines appeared with characteristic chromosome markers after approximately 40 cell population doublings. The initial karyotype recognized in T cells from the skin biopsy was 46,XY and the karyotypes of the continuous cell strains were 46,XY, -18, + i(18q) and another with multiple chromosome aberrations as described in Sezary T-cell leukemia. Phenotyping with monoclonal antibodies and T-cell receptor analysis indicates that the latter cell strain represents a minority of T-cells in the plaque. Due to its many chromosomal aberrations it probably represents the malignant cell, which may be a central cell in the immune stimulation taking place in the skin.

Cloning, characterization, and autoimmune recognition of rat islet glutamic acid decarboxylase in insulin-dependent diabetes mellitus

A 64-kDa islet protein is a major autoantigen in insulin-dependent diabetes mellitus (IDDM). Autoantibodies against the 64-kDa protein were recently shown to immunoprecipitate glutamic acid decarboxylase (GAD; L-glutamate 1-carboxy-lyase, EC 4.1.1.15) from brain and from islets. We present evidence that the autoantisera also recognize a hydrophilic islet protein of approximately 67 kDa in addition to the amphiphilic 64-kDa form. We have isolated a full-length rat islet GAD cDNA encoding a hydrophilic 67-kDa protein, which appears to be identical to rat brain 67-kDa GAD. A partial sequence of human insulinoma 67-kDa GAD was identical to human brain 67-kDa GAD. Allelic variations were observed in rat as well as in human 67-kDa GAD sequences. The expressed rat islet 67-kDa GAD protein is functional and is immunoprecipitated by IDDM sera; it comigrates electrophoretically with the 67-kDa islet autoantigen. The hydrophilic 67-kDa form of GAD in islets is an additional autoantigen in IDDM and is recognized by a different subset of autoantibodies than the 64-kDa autoantigen. Thus, mammalian cell lines expressing functionally active, recombinant GAD may become important tools to study the nature and the role of GAD autoreactivity in IDDM.

Molecular cloning and mammalian expression of human beta 2-glycoprotein I cDNA

Human beta 2-glycoprotein (beta 2gpI) cDNA was isolated from a liver cDNA library and sequenced. The cDNA encoded a 19-residue hydrophobic signal peptide followed by the mature beta 2gpI of 326 amino acid residues. In liver and in the hepatoma cell line HepG2 there are two mRNA species of about 1.4 and 4.3 kb, respectively, hybridizing specifically with the beta 2gpI cDNA. Upon isoelectric focusing, recombinant beta 2gpI obtained from expression of beta 2gpI cDNA in baby hamster kidney cells showed the same pattern of bands as beta 2gpI isolated from plasma, and at least 5 polypeptides were visible.

A short synthetic adaptor as second-strand primer in the construction of cDNA libraries by the vector-primer method

The construction of high quality cDNA libraries is one of the most important yet technically challenging procedures in the study of gene structure and function. The present report presents a simplification of the classical Okayama-Berg protocol for the construction of plasmid libraries. The introduction of a short synthetic oligonucleotide as a second-strand adaptor facilitates the optimization of library construction and allows for quick adaptation of almost any vector as a cDNA cloning vehicle.

Calcium binding in alpha-amylases: an X-ray diffraction study at 2.1-A resolution of two enzymes from Aspergillus

X-ray diffraction analysis (at 2.1-A resolution) of an acid alpha-amylase from Aspergillus niger allowed a detailed description of the stereochemistry of the calcium-binding sites. The primary site (which is essential in maintaining proper folding around the active site) contains a tightly bound Ca2+ with an unusually high number of eight ligands (O delta 1 and O delta 2 of Asp175, O delta of Asn121, main-chain carbonyl oxygens of Glu162 and Glu210, and three water molecules). A secondary binding site was identified at the bottom of the substrate binding cleft; it involves the residues presumed to play a catalytic role (Asp206 and Glu230). This explains the inhibitory effect of calcium observed at higher concentrations. Neutral Aspergillus oryzae (TAKA) alpha-amylase was also refined in a new crystal at 2.1-A resolution. The structure of this homologous (over 80%) enzyme and additional kinetic studies support all the structural conclusions regarding both calcium-binding sites.

Expression of human alpha 2-macroglobulin cDNA in baby hamster kidney fibroblasts: secretion of high levels of active alpha 2-macroglobulin

Human alpha 2-macroglobulin (alpha 2M) is a unique 720-kDa proteinase inhibitor with a broad specificity. Unlike most other proteinase inhibitors, it does not inhibit proteolytic activity by blocking the active site of the proteinase. During complex formation with a proteinase, alpha 2M entraps the proteinase molecule in a reaction that involves large conformational changes in alpha 2M. We describe the molecular cloning of alpha 2M cDNA from the human hepatoblastoma cell line HepG2. The cDNA was subcloned under control of the adenovirus major late promoter in a mammalian expression vector and introduced into the baby hamster kidney (BHK) cell line. Transformed clones were isolated and tested for production of human alpha 2M with a specific enzyme-linked immunosorbent assay. Human recombinant alpha 2M (r alpha 2M), secreted and purified from isolated transfected BHK cell lines, was structurally and functionally compared to alpha 2M purified from human serum. The results show that r alpha 2M was secreted from the BHK cells as an active proteinase-binding tetramer with functional thiol esters. Cleavage reactions of r alpha 2M with methylamine and trypsin showed that the recombinant product, which was correctly processed at the N-terminus, exhibited molecular characteristics similar to those of the human serum derived reference. Moreover, r alpha 2M-trypsin complex bound to purified human placental alpha 2M receptor with an affinity indistinguishable from that of a complex formed from serum-derived alpha 2M and trypsin.

Quenching of the amidolytic activity of one-chain tissue-type plasminogen activator by mutation of lysine-416

In contrast to most other serine proteases, tissue-type plasminogen activator (t-PA) possesses enzymatic activity as the one-chain zymogen form. The hypothesis that lysine residues 277 or 416 may be involved in stabilization of an active conformation of one-chain t-PA via salt-bridge formation with aspartic acid residue 477 was tested by site-directed mutagenesis. Four recombinant t-PA mutants were constructed. The amidolytic activities of these analogues were compared to that of authentic t-PA. Substitution of arginine-275 provided an analogue [( R275G]t-PA) resistant to plasmin cleavage. The amidolytic activity of [R275G]t-PA was comparable to that of authentic one-chain t-PA, and so was the activity of [R275L,K277L]t-PA, in which additional substitution of lysine residue 277 was carried out. This suggested that its presence was nonessential for obtaining one-chain t-PA activity. In contrast, substitution of lysine residue 416 to obtain [K416S]t-PA and [K416S,H417T]t-PA resulted in substantial quenching of amidolytic one-chain activity. As expected, the amidolytic activities of the two-chain forms were less affected by the substitution. Involvement of lysine residue 416 in one-chain t-PA activity was also indicated by decreased activities of [K416S]t-PA and [K416S,H417T]t-PA with plasminogen as the substrate. The one-chain activity of the lysine residue 416 substitution analogues was partially restored in the presence of fibrin. This could indicate that strong ligands such as fibrin might provide an alternative stabilization of the active conformation of one-chain t-PA.

Partial processing of the neuropeptide Y precursor in transfected CHO cells

The activation of regulatory peptides by post-translational modification of their biosynthetic precursors is generally thought to occur only in neuroendocrine cells. We have selected clones of Chinese hamster ovary cells, a non-neuroendocrine cell line, which were transfected with a eukaryotic expression vector coding for the precursor for neuropeptide Y. Although the majority of the immunoreactive NPY was found in the form of pro-NPY, some degree of intracellular proteolytic processing of the precursor occurred in all clones. Part of the intracellular NPY immunoreactivity was even correctly amidated. Extracellular degradation of pro-NPY in the tissue culture medium generated immunoreactivity which corresponded in size to NPY. It is concluded that precursor processing can occur in non-neuroendocrine cells both as a biological process within the cells and as apparent processing, degradation in the tissue culture medium.

Rhizomucor miehei triglyceride lipase is processed and secreted from transformed Aspergillus oryzae

The cDNA encoding the precursor of the Rhizomucor miehei triglyceride lipase was inserted in an Aspergillus oryzae expression vector. In this vector the expression of the lipase cDNA is under control of the Aspergillus oryzae alpha-amylase gene promoter and the Aspergillus niger glucoamylase gene terminator. The recombinant plasmid was introduced into Aspergillus oryzae, and transformed colonies were selected and screened for lipase expression. Lipase-positive transformants were grown in a small fermentor, and recombinant triglyceride lipase was purified from the culture broth. The purified enzymatically active recombinant lipase (rRML) secreted from A. oryzae was shown to have the same characteristics with respect to mobility on reducing SDS-gels and amino acid composition as the native enzyme. N-terminal amino acid sequencing indicated that approximately 70% of the secreted rRML had the same N-terminal sequence as the native Rhizomucor miehei enzyme, whereas 30% of the secreted rRML was one amino acid residue shorter in the N-terminal. The recombinant lipase precursor, which has a 70 amino acid propeptide, is thus processed in and secreted from Aspergillus oryzae. We have hereby demonstrated the utility of this organism as a host for the production of recombinant triglyceride lipases.