Expression of human angiogenin in cultured baby hamster kidney cells

Hypoxic conditions stimulate the production of angiogenin and vascular endothelial growth factor by human renal proximal tubular epithelial cells in culture

BACKGROUND

Chronic low oxygen in the tubulointerstitial area is a crucial cause of renal degradation and tubulointerstitial damage. Previous reports have suggested that the maintenance of renal blood flow plays a role in the suppression of progressive renal damage. Neovascularization is important for the maintenance of blood flow. We studied the production of angiogenic factors by culturing renal proximal tubular epithelial cells (PTEC) under hypoxic conditions.

METHODS

Cultured PTEC were exposed to normal and low-oxygen conditions. The levels of angiogenin (ANG) and vascular endothelial growth factor (VEGF) in the cell supernatants were measured by enzyme-linked immunosorbent assay. The messenger RNAs (mRNAs) of ANG and VEGF in the PTEC were examined by real-time reverse transcriptase polymerase chain reaction (real-time RT-PCR). The presence of ANG, VEGF and hypoxia-inducible factor-1 (HIF-1) was studied by immunofluorescence techniques. The effect of cobalt chloride (CoCl(2)), which is an HIF-1 inducer, on the production of ANG and VEGF was also examined in order to elucidate the contribution of the HIF-1 pathway to the production of these cytokines.

RESULTS

ANG and VEGF were demonstrated to exist in the cell supernatants, and ANG and VEGF mRNAs were detected in the PTEC. Hypoxic conditions stimulated the secretion of ANG (2.5-fold vs normoxia, P<0.001) and VEGF (3.2-fold vs normoxia, P<0.001) by PTEC. Hypoxic conditions increased the mRNA expression of ANG for 6 h (1.38-fold vs normoxia, P<0.05) and VEGF for 24 h (2.04-fold vs normoxia, P<0.01). Hypoxic conditions also enhanced ANG, VEGF and HIF-1 protein expression in PTEC. The CoCl(2) increased the secretion of ANG (5.2-fold vs control, P<0.0001) and VEGF (2.3-fold vs control, P<0.0001) by PTEC.

CONCLUSION

Under hypoxic conditions, the ANG and VEGF secreted by PTEC may modulate angiogenesis and vascular remodeling in the renal interstitium via an increase in the production of HIF-1.

Internalization and processing of human angiogenin by cultured aortic smooth muscle cells

Human angiogenin is a 14-kDa plasma protein with angiogenic and ribonucleolytic activities. Angiogenin binds specifically to aortic smooth muscle cells, activates second messenger pathways, and inhibits their proliferation. Human and bovine aortic smooth muscle cells were used to study the internalization and intracellular fate of human angiogenin at 37 degrees C. Using a specific antibody against angiogenin, we found that the internalized native protein was localized in the perinuclear region at 30 min and then dispersed throughout the cytoplasm. In conditions favoring receptor-mediated endocytosis, internalization of iodinated angiogenin showed a first peak at 5 min and then further increased for up to 24 h. The half-life of the molecule, calculated as 12 h in chase experiments, could contribute to its intracellular accumulation. In cell extracts, in addition to the 14-kDa protein, a 8.7-kDa fragment was observed at 24 h, and three fragments with molecular mass of 10.5, 8.7, and 6. 1 kDa were detected at 48 h. Our data point to a specific internalization and processing of human angiogenin by aortic smooth muscle cells.

Expression of receptors for human angiogenin in vascular smooth muscle cells

Human angiogenin is a plasma protein with angiogenic and ribonucleolytic activities. Angiogenin inhibited both DNA replication and proliferation of aortic smooth muscle cells. Binding of 125I-angiogenin to bovine aortic smooth muscle cells at 4 degrees C was specific, saturable, reversible and involved two families of interactions. High-affinity binding sites with an apparent dissociation constant of 0.2 nm bound 1 x 104 molecules per cell grown at a density of 3 x 104.cm-2. Low-affinity binding sites with an apparent dissociation constant of 0.1 micrometer bound 4 x 106 molecules.cell-1. High-affinity binding sites decreased as cell density increased and were not detected at confluence. 125I-angiogenin bound specifically to cells routinely grown in serum-free conditions, indicating that the angiogenin-binding components were cell-derived. Affinity labelling of sparse bovine smooth muscle cells yielded seven major specific complexes of 45, 52, 70, 87, 98, 210 and 250-260 kDa. The same pattern was obtained with human cells. Potential modulators of angiogenesis such as protamine, heparin and the placental ribonuclease inhibitor competed for angiogenin binding to the cells. Together these data suggest that cultured bovine and human aortic smooth muscle cells express specific receptors for human angiogenin.

Chimeric anti-angiogenin antibody cAb 26-2F inhibits the formation of human breast cancer xenografts in athymic mice

Angiogenin (Ang), an inducer of neovascularization, is secreted by several types of human tumor cells and appears critical for their growth. The murine anti-Ang monoclonal antibody (mAb) 26-2F neutralizes the activities of Ang and dramatically prevents the establishment and metastatic dissemination of human tumor cell xenografts in athymic mice. However, for use clinically, the well-documented problem of the human anti-globulin antibody response known to occur with murine antibodies requires resolution. As a result, chimeric as well as totally humanized antibodies are currently being evaluated as therapeutic agents for the treatment of several pathological conditions, including malignancy. Therefore, we have constructed a chimeric mouse/human antibody based on the structure of mAb 26-2F. Complementary DNAs from the light and heavy chain variable regions of mAb 26-2F were cloned, sequenced, and genetically engineered by PCR for subcloning into expression vectors that contain human constant region sequences. Transfection of these vectors into nonproducing mouse myeloma cells resulted in the secretion of fully assembled tetrameric molecules. The chimeric antibody (cAb 26-2F) binds to Ang and inhibits its ribonucleolytic and angiogenic activities as potently as mAb 26-2F. Furthermore, the capacities of cAb 26-2F and its murine counterpart to suppress the formation of human breast cancer tumors in athymic mice are indistinguishable. Thus cAb 26-2F, with its retained neutralization capability and likely decreased immunogenicity, may be of use clinically for the treatment of human cancer and related disorders where pathological angiogenesis is a component.

A monoclonal antibody to human angiogenin. Inhibition of ribonucleolytic and angiogenic activities and localization of the antigenic epitope

A monoclonal antibody (mAb) to human angiogenin, a protein that induces formation of new blood vessels, was produced by somatic cell fusion techniques and designated as 26-2F. It is an IgGl kappa whose binding affinity, expressed as an IC50, is (1.6 +/- 0.1) x 10(-9) M as determined by a competition radioimmunoassay. mAb 26-2F neutralizes the ribonucleolytic activity of angiogenin as assessed by in vitro protein synthesis and tRNA degradation assays. It also effectively inhibits neovascularization induced by angiogenin on the chick chorioallantoic membrane. Epitope mapping indicates that the binding region of angiogenin recognized by mAb 26-2F is discontinuous and involves both Trp-89 and residues in the segment 38-41. This epitope is formed by two surface loops which are juxtaposed in the three-dimensional structure of human angiogenin recently determined by X-ray crystallography. Thus mAb 26-2F, along with similar antibodies under investigation, will facilitate structure/function studies of angiogenin, help define its physiological role, and lead to an understanding of the consequences of its inhibition in pathological situations in which angiogenin may be involved.

Characterization and sequencing of rabbit, pig and mouse angiogenins: discernment of functionally important residues and regions

Rabbit, pig and mouse angiogenins have been purified from blood serum and characterized, and the rabbit and pig proteins have been sequenced fully. A partial sequence of the mouse protein is consistent with the sequence deduced from the genomic DNA (Bond, M.D. and Vallee, B.L. (1990) Biochem. Biophys. Res. Commun. 171, 988-995). All three angiogenins are homologous to the pancreatic RNases and contain the essential catalytic residues His-13, Lys-40 and His-114, and the 6 half-cystines of the human protein. Like human angiogenin they display extremely low ribonucleolytic activities toward wheat-germ RNA, yeast RNA, poly(C) and poly(U). The rabbit and pig proteins induce neovascularization in vivo and also inhibit protein synthesis in vitro. The interaction of rabbit, pig and bovine angiogenins with placental ribonuclease inhibitor, a potent inhibitor of angiogenin, was examined by fluorescence spectroscopy. Rate and equilibrium binding constants indicate that rabbit angiogenin binds to the inhibitor much like human angiogenin, whereas the pig and bovine proteins show significant differences. A comparison of the five angiogenin sequences now available points to specific residues that are highly conserved among them but differ from the corresponding residues in the RNases. These residues are clustered in particular regions of the three-dimensional structure, two of which contribute to the angiogenic, second-messenger and/or protein synthesis inhibition activities of human angiogenin.

Cis proline mutants of ribonuclease A. I. Thermal stability

A chemically synthesized gene for ribonuclease A has been expressed in Escherichia coli using a T7 expression system (Studier, F.W., Rosenberg, A.H., Dunn, J.J., & Dubendorff, J.W., 1990, Methods Enzymol. 185, 60-89). The expressed protein, which contains an additional N-terminal methionine residue, has physical and catalytic properties close to those of bovine ribonuclease A. The expressed protein accumulates in inclusion bodies and has scrambled disulfide bonds; the native disulfide bonds are regenerated during purification. Site-directed mutations have been made at each of the two cis proline residues, 93 and 114, and a double mutant has been made. In contrast to results reported for replacement of trans proline residues, replacement of either cis proline is strongly destabilizing. Thermal unfolding experiments on four single mutants give delta Tm approximately equal to 10 degrees C and delta delta G0 (apparent) = 2-3 kcal/mol. The reason is that either the substituted amino acid goes in cis, and cis<==>trans isomerization after unfolding pulls the unfolding equilibrium toward the unfolded state, or else there is a conformational change, which by itself is destabilizing relative to the wild-type conformation, that allows the substituted amino acid to form a trans peptide bond.

Dual site model for the organogenic activity of angiogenin

The residues that are indispensable for the ribonucleolytic activity of angiogenin are also known to be essential for its angiogenic activity. We now demonstrate that residues in another region of the protein, devoid of catalytic residues, are additionally required for angiogenesis. Endoproteinase Lys-C or a baby hamster kidney cell protease cleaves angiogenin at the peptide bond either between Lys-60 and Asn-61 or between Glu-67 and Asn-68, respectively. The two polypeptide fragments resulting from either cleavage remain linked by disulfide bonds. These two derivatives and des-(Asn61-Glu67)-angiogenin--in which both bonds are cleaved--retain their ribonucleolytic activities toward tRNA, 18S and 28S rRNA, and dinucleoside phosphates but are no longer angiogenic on the chicken embryo chorioallantoic membrane. Further, their capacity to elicit a second messenger response in endothelial cells is greatly decreased. Moreover, none of these three derivatives inhibit angiogenin-induced angiogenesis. This contrasts with two active site mutants of angiogenin. These results identify the residues from 60 to 68 as a region of angiogenin that is part of a cell-surface receptor binding site [see accompanying manuscript: Hu, G.-F., Chang, S.-I., Riordan, J.F. & Vallee, B.L. (1991) Proc. Natl. Acad. Sci. USA 88, 2227-2231] and serve as the basis for a dual site model of the organogenic activity of angiogenin.

Interaction of human placental ribonuclease with placental ribonuclease inhibitor

The interactions of human placental ribonuclease inhibitor (PRI) with bovine pancreatic ribonuclease (RNase) A and human angiogenin, a plasma protein that induces blood vessel formation, have been characterized in detail in earlier studies. However, studies on the interaction of PRI with the RNase(s) indigenous to placenta have not been performed previously, nor have any placental RNases been identified. In the present work, the major human placental RNase (PR) was purified to homogeneity by a five-step procedure and was obtained in a yield of 110 micrograms/kg of tissue. The placental content of angiogenin was also examined and was found to be at least 10-fold lower than that of PR. On the basis of its amino acid composition, amino-terminal sequence, and catalytic properties, PR appears to be identical with an RNase previously isolated from eosinophils (eosinophil-derived neurotoxin), liver, and urine. The apparent second-order rate constant of association for the PR.PRI complex, measured by examining the competition between PR and angiogenin for PRI, is 1.9 X 10(8) M-1 s-1. The rate constant for dissociation of the complex, determined by HPLC measurement of the rate of release of PR from its complex with PRI in the presence of a scavenger for free PRI, is 1.8 X 10(-7) s-1. Thus the Ki value for the PR.PRI complex is 9 X 10(-16) M, similar to that obtained with angiogenin, and 40-fold lower than that measured with RNase A. Complex formation causes a small red shift in the protein fluorescence emission spectrum, with no significant change in overall intensity. The fluorescence quantum yield of PR and the Stern-Volmer constant for fluorescence quenching by acrylamide are both high, possibly due to the presence of an unusual posttranslationally modified tryptophan residue at position 7 in the primary sequence.

Purification and characterization of recombinant human testis angiotensin-converting enzyme expressed in Chinese hamster ovary cells

Enzymatically active human testis angiotensin-converting enzyme (ACE) was expressed in Chinese hamster ovary (CHO) cells stably transfected with each of three vectors: p omega-ACE contains a full-length testis ACE cDNA under the control of a retroviral promoter; and pLEN-ACEVII and pLEN-ACE6/5, in which full-length and membrane anchor-minus testis ACE cDNAs, respectively, are under the control of the human metallothionein IIA promoter and SV40 enhancer. In every case, active recombinant human testis ACE (hTACE) was secreted in a soluble form into the culture media, up to 2.4 mg/liter in the media of metal-induced, high-producing clones transfected with one of the pLEN vectors. In addition, membrane-bound recombinant enzyme was recovered from detergent extracts of cell pellets of CHO cells transfected with either p omega-ACE or pLEN-ACE-VII. Recombinant converting enzyme was purified to homogeneity by single-step affinity chromatography of conditioned media and detergent-extracted cell pellets in 85 and 70% overall yield, respectively. Purified hTACE from all sources comigrated with the native testis isozyme on sodium dodecyl sulfate-polyacrylamide gel electrophoresis with M(r) approximately 100 kDa. The native and recombinant proteins cross-reacted equally with anti-human kidney ACE antiserum on Western blotting. The catalytic activity of recombinant angiotensin-converting enzyme, in terms of angiotensin I and 2-furanacryloyl-Phe-Gly-Gly hydrolysis, chloride activation, and lisinopril inhibition, was essentially identical to that of the native enzyme. The facile recovery in high yield of fully active hTACE from the media of stably transfected CHO cells provides a suitable system for investigating structure-function relationships in this enzyme.

Replacement of residues 8-22 of angiogenin with 7-21 of RNase A selectively affects protein synthesis inhibition and angiogenesis

The region of human angiogenin containing residues 8-21 is highly conserved in angiogenins from four mammalian species but differs substantially from the corresponding region of the homologous protein ribonuclease A (RNase A). Regional mutagenesis has been employed to replace this segment of angiogenin with the corresponding RNase A sequence, and the activities of the resulting covalent angiogenin/RNase hybrid, designated ARH-III, have been examined. The ribonucleolytic activity of ARH-III is unchanged toward most substrates, including tRNA, naked 18S and 28S rRNA, CpA, CpG, UpA, and UpG. In contrast, the capacity of ARH-III to inhibit cell-free protein synthesis is decreased 20-30-fold compared to that of angiogenin. The angiogenic activity of ARH-III is also different; it is actually more potent. It induces a maximal response in the chick chorioallantoic membrane assay at 0.1 ng per egg, a 10-fold lower dose than required for angiogenin. In addition, binding of ARH-III to the placental ribonuclease inhibitor is increased by at least 1 order of magnitude (Ki less than or equal to 7 x 10(-17) M) compared to angiogenin. Thus, mutation of a highly conserved region of angiogenin markedly affects those properties likely involved in its biological function(s); it does not, however, alter ribonucleolytic activity toward most substrates.

Modular mutagenesis of human placental ribonuclease inhibitor, a protein with leucine-rich repeats

Human placental ribonuclease inhibitor (PRI) is a potent protein inhibitor of pancreatic ribonucleases and the homologous blood vessel-inducing protein angiogenin. Although inhibition by PRI occurs with a 1:1 stoichiometry, its primary structure is composed predominantly of seven internal leucine-rich repeats. These internal repeats were systematically deleted either singly or in combination by "modular" mutagenesis. Deletion of repeat units 3 plus 4 or repeat unit 6 results in mutants that both bind to and inhibit ribonuclease A. Therefore, the angiogenin/ribonuclease binding site in PRI must reside primarily or entirely in repeats 1, 2, 5, or 7, the short N- or C-terminal segments, or a combination of these. Deletion of repeat units 3-5, 5-6, or 5 alone results in mutants that exhibit only binding activity. Hence, the binding site cannot reside exclusively in repeat 5. Other internal deletions or N- or C-terminal deletions of 6-86% of the protein all abolish activity. These results suggest that PRI has a modular structure, with one primary structural repeat constituting one module. The approach taken may be applicable to other proteins with repeat structures.

Angiogenin activates phospholipase C and elicits a rapid incorporation of fatty acid into cholesterol esters in vascular smooth muscle cells

Angiogenin activates the phosphoinositide-specific phospholipase C (PLC) in cultured rat aortic smooth muscle cells to yield a transient (30 s) peak of 1,2-diacylglycerol (DG) and inositol trisphosphate. Within 1 min, the DG level falls below that of the control and remains so for at least 20 min. A transient increase in monoacylglycerol indicates that depletion of DG may be the consequence of hydrolysis by DG lipase. In addition to these changes in second messengers, a rapid increase in incorporation of radiolabeled tracer into cellular cholesterol esters is observed. Stimulated cholesterol ester labeling is inhibited by preincubation with either the DG lipase inhibitor RHC 80267 or the acyl coenzyme A:cholesterol acyltransferase inhibitor Sandoz 58035. Cells prelabeled with [3H]arachidonate show a sustained increase in labeling of cholesterol esters following exposure to angiogenin. In contrast, cells prelabeled with [3H]oleate show only a transient elevation that returns to the basal level by 5 min. This suggests initial cholesterol esterification by oleate followed by arachidonate that is released by stimulation of the PLC/DG lipase pathway.

C-terminal angiogenin peptides inhibit the biological and enzymatic activities of angiogenin

Synthetic peptides corresponding to the C-terminal region of angiogenin (Ang) inhibit the enzymatic and biological activities of the molecule while peptides from the N-terminal region do not affect either activity. The peptide Ang(108-121) transiently abolishes the inhibition of cell-free protein synthesis caused by angiogenin coincidentally with its cleavage of reticulocyte RNA. Several C-terminal peptides also inhibit nuclease activity of angiogenin when tRNA is the substrate. Furthermore, peptide Ang(108-123) significantly decreases neovascularization elicited by angiogenin in the chick chorioallantoic membrane assay.

Characterization of ribonucleolytic activity of angiogenin towards tRNA

Yeast tRNA is a convenient substrate for the assay of the ribonucleolytic activity of human angiogenin. The optimal pH, [NaCl], and temperature for tRNA cleavage by angiogenin are approximately 6.8, 15-30 mM, and approximately 55 degrees C, respectively, as compared with approximately 8.0, 100-200 mM, and approximately 65 degrees C, respectively, for RNase A. Polyanions and metals both inhibit angiogenin and RNase A but to different extents.

Binding of placental ribonuclease inhibitor to the active site of angiogenin

The importance of specific residues in angiogenin for binding to placental ribonuclease inhibitor (PRI) has been assessed by examining the interaction of angiogenin derivatives with PRI. PRI binds native angiogenin with a Ki value of 7.1 X 10(-16) M [Lee, F. S., Shapiro, R., & Vallee, B. L. (1989) Biochemistry 28, 225-230]. Substitution of a Gln for Lys-40 in angiogenin by site-specific mutagenesis decreases the association rate constant 3-fold and increases the dissociation rate constant 440-fold, resulting in a 1300-fold weaker Ki value. The half-life of the mutant.PRI complex is 3.4 h compared to approximately 60 days for the native angiogenin.PRI complex. The magnitude of the change in Ki value suggests that in the complex, Lys-40 forms a salt bridge or hydrogen bond with an anionic moiety in PRI. Carboxymethylation of His-13 or His-114 with bromoacetate increases the Ki value 15-fold, and oxidation of Trp-89 by means of dimethyl sulfoxide and hydrochloric acid increases it 2.4-fold, suggesting that these residues also form part of the contact region with PRI. The changes in Ki value reflect an increase in the dissociation rate constant. On the other hand, dinitrophenylation of either Lys-50 or Lys-60 with 1-fluoro-2,4-dinitrobenzene does not significantly alter the Ki value, suggesting that these residues are not part of the contact region. These results indicate that PRI inhibition minimally involves the three residues critical for the activity of angiogenin--Lys-40, His-13, and His-114--and to a lesser extent its single tryptophan, Trp-89.

Expression of human placental ribonuclease inhibitor in Escherichia coli

Human placental ribonuclease inhibitor (PRI) has been expressed in and isolated from Escherichia coli. Its apparent molecular weight, immunoreactivity and amino acid composition are virtually identical with those of native PRI. It inhibits the enzymatic activities of either angiogenin, a blood vessel inducing protein homologous to pancreatic RNase (RNase A), or RNase A in a stoichiometry of 1:1. Recombinant PRI binds to angiogenin and RNase A with Ki values of 2.9 x 10(-16) M and 6.8 x 10(-14) M, respectively, comparable to the affinities of native PRI for these enzymes. Thus, these results confirm that PRI inhibits angiogenin more effectively than RNase A.

A covalent angiogenin/ribonuclease hybrid with a fourth disulfide bond generated by regional mutagenesis

Human angiogenin is a blood vessel inducing protein whose primary structure displays 33% identity to that of bovine pancreatic ribonuclease A (RNase A). Angiogenin catalyzes limited cleavage of 18S and 28S ribosomal RNA and is several orders of magnitude less potent than RNase A toward conventional substrates. A striking structural difference between angiogenin and RNase is the virtual absence of sequence similarity within the region of RNase that contains the Cys-65--Cys-72 disulfide bond. Indeed, angiogenin lacks this disulfide linkage. The present report describes the use of regional mutagenesis to generate a covalent angiogenin/RNase hybrid protein, ARH-I, where residues 58-70 of angiogenin have been replaced by the corresponding segment of RNase A (residues 59-73). The protein expressed in Escherichia coli readily folds at pH 8.5 to form the four expected disulfide bonds. The in vivo angiogenic potency of ARH-I is markedly diminished compared with that of angiogenin when examined using the chick chorioallantoic membrane assay. In contrast, its enzymatic activity is dramatically increased. With high molecular weight wheat germ RNA and tRNA, ARH-I is 660- and 300-fold more active than angiogenin, respectively, while with poly(uridylic acid), poly(cytidylic acid), cytidylyl(3'----5')adenosine (CpA), and uridylyl(3'----5')adenosine (UpA) activity is enhanced by about 200-fold. In addition, the specificity of ARH-I toward dinucleoside 3',5'-phosphates is qualitatively similar to RNase A; while angiogenin prefers cytidylyl(3'----5')guanosine (CpG) to UpA, both RNase and the hybrid prefer UpA to CpG. ARH-I also displays greater than 10-fold enhanced activity toward rRNA in intact ribosomes, while abolishing the capacity of the ribosome to support cell-free protein synthesis. The enhanced enzymatic properties of ARH-I parallel a 2-fold increase in chemical reactivity of active-site lysine and histidine residues based on rates of chemical modification. The data indicate that introduction of a region of RNase A containing the Cys-65--Cys-72 disulfide bond into angiogenin dramatically increases RNase-like enzymatic activity while reducing its angiogenicity.

Role of lysines in human angiogenin: chemical modification and site-directed mutagenesis

The role of lysines in the ribonucleolytic and angiogenic activities of human angiogenin has been examined by chemical modification and site-directed mutagenesis. It was demonstrated previously [Shapiro, R., Weremowicz, S., Riordan, J.F., & Vallee, B.L. (1987) Proc. Natl. Acad. Sci. U.S.A. 84, 8783-8787] that extensive treatment with lysine reagents markedly decreases the ribonucleolytic activity of angiogenin. In the present study, limited chemical modification with 1-fluoro-2,4-dinitrobenzene followed by C18 high-performance liquid chromatography yielded several (dinitrophenyl)angiogenin derivaties. The major derivative formed had slightly increased enzymatic activity compared with the unmodified protein. Tryptic peptide mapping demonstrated the site of modification to be Lys-50. A second derivative, modified at Lys-60, was 34% active. Analysis of a third derivative indicated that modification of Lys-82 did not decrease activity. Thus, Lys-50 and Lys-82 are unessential for enzymatic activity while Lys-60 may play a minor role. No pure derivative modified at Lys-40, corresponding to the active-site residue Lys-41 of the homologous protein ribonuclease A, could be obtained by chemical procedures. Therefore, we employed oligonucleotide-directed mutagenesis to replace this lysine with glutamine or arginine. The Gln-40 derivative had less than 0.05% enzymatic activity compared with the unmodified protein and substantially reduced angiogenic activity when examined with the chick embryo chorioallantoic membrane assay. These results suggest that the angiogenic activity of the protein is dependent on an intact enzymatic active site. The Arg-40 derivative had 2.2% ribonucleolytic activity compared with unmodified angiogenin. The effects of reductive methylation of this derivative indicate that no lysines other than Lys-40 are critical.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of Met-(-1) angiogenin in Escherichia coli: conversion to the authentic less than Glu-1 protein

A method for obtaining authentic human angiogenin utilizing an Escherichia coli recombinant expression system is described. A synthetic gene encoding angiogenin was placed into a vector for direct expression under the control of a modified E. coli trp promoter. The protein was produced by the bacteria in an insoluble form and purified to homogeneity by cation-exchange and reversed-phase HPLC following reduction/solubilization and reoxidation. The protein isolated was identified as Met-(-1) angiogenin by amino acid analysis and tryptic peptide mapping; the latter demonstrated that all three disulfide bonds had formed correctly. Both the enzymatic and angiogenic activities of the Met-(-1) protein were equivalent to those of native angiogenin. A Met-(-1) Leu-30 derivative of angiogenin was also isolated and found to be fully active. Conversion of Met-(-1) angiogenin to the authentic less than Glu-1 protein was achieved by treatment with Aeromonas aminopeptidase under conditions in which the new N-terminal glutamine readily cyclizes nonenzymatically. This aminopeptidase treatment may have more general applicability for removal of undesirable N-terminal methionine residues from foreign proteins expressed in bacteria.