Hemoglobin Providence. A human hemoglobin variant occurring in two forms in vivo.
Hemoglobin Providence Asn and Hemoglobin Providence Asp are two abnormal hemoglobins which apparently arise from a single genetic change that substitutes asparagine for lysine at position 82 (EF6) in the beta chain of human hemoglobin. The second form appears to be thr result of a partial in vivo deamidation of the asparagine situated at position beta 82. Cellulose acetate and citrate agar electrophoresis of hemolysates from patients with this abnormality shows three bands. Globin chain electrophoresis at acid and alkaline pH shows three beta chains. These three chains correspond to the normal beta A chain and two abnormal beta chains. Sequence analysis indicates that the two abnormal chains differ from beta A at only position beta 82. In the two abnormal chains, the residue which is normally lysine is substituted either by asparagine or by aspartic acid. These substitutions are notable because beta 82 lysine is one of the residues involved in 2,3-diphosphoglycerate binding. Additionally, beta 82 lysine is typically invariant in hemoglobin beta chain sequences. Sequence data on the two forms of Hemoglobin Providence are given in this paper. The functional properties of these two forms are described in the next paper. (+info)
Merbarone, a catalytic inhibitor of DNA topoisomerase II, induces apoptosis in CEM cells through activation of ICE/CED-3-like protease.
Merbarone (5-[N-phenyl carboxamido]-2-thiobarbituric acid) is an anticancer drug that inhibits the catalytic activity of DNA topoisomerase II (topo II) without damaging DNA or stabilizing DNA-topo II cleavable complexes. Although the cytotoxicity of the complex-stabilizing DNA-topo II inhibitors such as VP-16 (etoposide) has been partially elucidated, the cytotoxicity of merbarone is poorly understood. Here, we report that merbarone induces programmed cell death or apoptosis in human leukemic CEM cells, characterized by internucleosomal DNA cleavage and nuclear condensation. Treatment of CEM cells with apoptosis-inducing concentrations of merbarone caused activation of c-Jun NH2-terminal kinase/stress-activated protein kinase, c-jun gene induction, activation of caspase-3/CPP32-like protease but not caspase-1, and the proteolytic cleavage of poly(ADP-ribose) polymerase. Treatment of CEM cells with a potent inhibitor of caspases, Z-Asp-2. 6-dichlorobenzoyloxymethyl-ketone, inhibited merbarone-induced caspase-3/CPP32-like activity and apoptosis in a dose-dependent manner. These results indicate that the catalytic inhibition of topo II by merbarone leads to apoptotic cell death through a caspase-3-like protease-dependent mechanism. These results further suggest that c-Jun and c-Jun NH2-terminal kinase/stress-activated protein kinase signaling may be involved in the cytotoxicity of merbarone. (+info)
Distortion of the L-->M transition in the photocycle of the bacteriorhodopsin mutant D96N: a time-resolved step-scan FTIR investigation.
The D96N mutant of bacteriorhodopsin has often been taken as a model system to study the M intermediate of the wild type photocycle due to the long life time of the corresponding intermediate of the mutant. Using time-resolved step-scan FTIR spectroscopy in combination with a sample changing wheel we investigated the photocycle of the mutant with microsecond time resolution. Already after several microseconds an intermediate similar to the MN state is observed, which contrasts with the M state of the wild type protein. At reduced hydration M and N intermediates similar to those of wild type BR can be detected. These results have a bearing on the interpretation of the photocycle of this mutant. A mechanism is suggested for the fast rise of MN which provides some insight into the molecular events involved in triggering the opening of the cytosolic channel also of the wild type protein. (+info)
Interaction of asparagine and EGF in the regulation of ornithine decarboxylase in IEC-6 cells.
Our laboratory has shown that asparagine (ASN) stimulates both ornithine decarboxylase (ODC) activity and gene expression in an intestinal epithelial cell line (IEC-6). The effect of ASN is specific, and other A- and N-system amino acids are almost as effective as ASN when added alone. In the present study, epidermal growth factor (EGF) was unable to increase ODC activity in cells maintained in a salt-glucose solution (Earle's balanced salt solution). However, the addition of ASN (10 mM) in the presence of EGF (30 ng/ml) increased the activity of ODC 0.5- to 4-fold over that stimulated by ASN alone. EGF also showed induction of ODC with glutamine and alpha-aminoisobutyric acid, but ODC induction was maximum with ASN and EGF. Thus the mechanism of the interaction between ASN and EGF is important for understanding the regulation of ODC under physiological conditions. Therefore, we examined the expression of the ODC gene and those for several protooncogenes under the same conditions. Increased expression of the genes for c-Jun and c-Fos but not for ODC occurred with EGF alone. The addition of ASN did not further increase the expression of the protooncogenes, but the combination of EGF and ASN further increased the expression of ODC over that of ASN alone. Western analysis showed no significant difference in the level of ODC protein in Earle's balanced salt solution, ASN, EGF, or EGF plus ASN. Addition of cycloheximide during ASN and ASN plus EGF treatment completely inhibited ODC activity without affecting the level of ODC protein. These results indicated that 1) the increased expression of protooncogenes in response to EGF is independent of increases in ODC activity and 2) potentiation between EGF and ASN on ODC activity may not be due to increased gene transcription but to posttranslational regulation and the requirement of ongoing protein synthesis involving a specific factor dependent on ASN. (+info)
Glycosylation of asparagine-28 of recombinant staphylokinase with high-mannose-type oligosaccharides results in a protein with highly attenuated plasminogen activator activity.
The properties of recombinant staphylokinase (SakSTAR) expressed in Pichia pastoris cells have been determined. The single consensus N-linked oligosaccharide linkage site in SakSTAR (at Asn28 of the mature protein) was occupied in approximately 50% of the expressed protein with high-mannose-type oligosaccharides. The majority of these glycans ranged in polymerization state from Man8GlcNAc2 to Man14GlcNAc2, with the predominant species being Man10GlcNAc2 and Man11GlcNAc2. Glycosylated SakSTAR (SakSTARg) did not differ from its aglycosyl form in its aggregation state in solution, its thermal denaturation properties, its ability to form a complex with human plasmin (hPm), the amidolytic properties of the respective SakSTAR-hPm complexes, or its ability to liberate the amino-terminal decapeptide required for formation of a functional SakSTAR-hPm plasminogen activator complex. However, this latter complex with SakSTARg showed a greatly reduced ability to activate human plasminogen (hPg) as compared with the same complex with the aglycosyl form of SakSTAR. We conclude that glycosylation at Asn28 does not affect the structural properties of SakSTAR or its ability to participate in the formation of an active enzymatic complex with hPm, but it is detrimental to the ability of the SakSTAR-hPm complex to serve as a hPg activator. This is likely due to restricted access of hPg to the active site of the SakSTARg-hPm complex. (+info)
The presence of pseudouridine in the anticodon alters the genetic code: a possible mechanism for assignment of the AAA lysine codon as asparagine in echinoderm mitochondria.
It has been inferred from DNA sequence analyses that in echinoderm mitochondria not only the usual asparagine codons AAU and AAC, but also the usual lysine codon AAA, are translated as asparagine by a single mitochondrial (mt) tRNAAsn with the anticodon GUU. Nucleotide sequencing of starfish mt tRNAAsn revealed that the anticodon is GPsiU, U35 at the anticodon second position being modified to pseudouridine (Psi). In contrast, mt tRNALys, corresponding to another lysine codon, AAG, has the anticodon CUU. mt tRNAs possessing anti-codons closely related to that of tRNAAsn, but responsible for decoding only two codons each-tRNAHis, tRNAAsp and tRNATyr-were found to possess unmodified U35 in all cases, suggesting the importance of Psi35 for decoding the three codons. Therefore, the decoding capabilities of two synthetic Escherichia coli tRNAAla variants with the anticodon GPsiU or GUU were examined using an E.coli in vitro translation system. Both tRNAs could translate not only AAC and AAU with similar efficiency, but also AAA with an efficiency that was approximately 2-fold higher in the case of tRNAAlaGPsiU than tRNAAlaGUU. These findings imply that Psi35 of echinoderm mt tRNAAsn actually serves to decode the unusual asparagine codon AAA, resulting in the alteration of the genetic code in echinoderm mitochondria. (+info)
L-Asparagine synthetase in serum as a marker for neoplasia.
L-Asparagine synthetase appears in serum approximately 7 days after the s.c. implantation of 1 X 10(5) cells of Leukemia 5178Y/AR (resistant to L-asparaginase) and increases in activity as the neoplasm grows and metastasizes. The principal source of the enzyme is the primary tumor. After intravranial inoculation of tumor, the rate of leakage of the enzyme is more pronounced than when the subcutaneous, intramuscular, or intraperitoneal routes are used. 1-(2-Chloroethyl)-3-cyclohexyl-1-nitrosourea (NSC 79037), a nitro-sourea effective in the palliation of L5178Y/AR, temporarily halts the influx of enzyme into the blood stream, as does surgical excision of the s.c. tumor nodules. Treatment of mice with L-asparaginase within 24 hr of inoculation of the tumor markedly augments both tumor growth and the rate of penetration of L-asparagine synthetase into the circulation. Several other L-asparagine synthetase into the circulation. Several other L-asparaginase-resistant tumors also were found to spill L-asparagine synthetase into the serum, but the correlation between this phenomenon and the specific activity of the enzyme in homogenates of the tumor was imperfect. (+info)
Conserved polar residues in the transmembrane domain of the human tachykinin NK2 receptor: functional roles and structural implications.
We have studied the effects of agonist and antagonist binding, agonist-induced activation and agonist-induced desensitization of the human tachykinin NK2 receptor mutated at polar residues Asn-51 [in transmembrane helix 1 (TM1)], Asp-79 (TM2) and Asn-303 (TM7), which are highly conserved in the transmembrane domain in the rhodopsin family of G-protein-coupled receptors. Wild-type and mutant receptors were expressed in both COS-1 cells and Xenopus oocytes. The results show that the N51D mutation results in a receptor which, in contrast with the wild-type receptor, is desensitized by the application of a concentration of 1 microM of the partial agonist GR64349, indicating that the mutant is more sensitive to agonist activation than is the wild-type receptor. In addition, we show that, whereas the D79E mutant displayed activation properties similar to those of the wild-type receptor, the D79N and D79A mutants displayed a severely impaired ability to activate the calcium-dependent chloride current. This suggests that it is the negative charge at Asn-79, rather than the ability of this residue to hydrogen-bond, that is critical for the activity of the receptor. Interestingly, the placement of a negative charge at position 303 could compensate for the removal of the negative charge at position 79, since the double mutant D79N/N303D displayed activation properties similar to those of the wild-type receptor. This suggests that these two residues are functionally coupled, and may even be in close proximity in the three-dimensional structure of the human tachykinin NK2 receptor. A three-dimensional model of the receptor displaying this putative interaction is presented. (+info)