Effects of the quantity sigma TS on the spin structure functions of nucleons in the resonance region.
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Journal Article↗
Biomedical subjects
Z Li
Publications and source records attributed to Z Li.
Novel peptidyl alpha-keto amide inhibitors of calpains and other cysteine proteases.
A series of new dipeptidyl alpha-keto amides of the general structure R1-L-Leu-D,L-AA-CONH-R2 were synthesized and evaluated as inhibitors for the cysteine proteases calpain I, calpain II, and cathepsin B. They combine 10 different N-protecting groups (R1), 3 amino acids residues in P1 (AA), and 44 distinct substituents on the alpha-keto amide nitrogen (R2). In general, calpain II was more sensitive to these inhibitors than calpain I, with a large number of inhibitors displaying dissociation constants (Ki) in the 10-100 nM range. Calpain I was also effectively inhibited, but very low Ki values were observed with a smaller number of inhibitors than with calpain II. Cathepsin B was weakly inhibited by most compounds in this study. The best inhibitors for calpain II were Z-Leu-Abu-CONH-CH2-CHOH-C6H5 (Ki = 15 nM), Z-Leu-Abu-CONH-CH2-2-pyridyl (Ki = 17 nM), and Z-Leu-Abu-CONH-CH2-C6H3(3,5(OMe)2) (Ki = 22 nM). The best calpain I inhibitor in this study was Z-Leu-Nva-CONH-CH2-2-pyridyl (Ki = 19 nM). The peptide alpha-keto amide Z-Leu-Abu-CONH-(CH2)2-3-indolyl was the best inhibitor for cathepsin B (Ki = 31 nM). Some compounds acted as specific calpain inhibitors, with comparable activity on both calpains I and II and a lack of activity on cathepsin B (e.g., 40, 42, 48, 70). Others were specific inhibitors for calpain I (e.g., 73) or calpain II (e.g., 18, 19, 33, 35, 56). Such inhibitors may be useful in elucidating the physiological and pathological events involving these proteases and may become possible therapeutic agents.
Animals↗
Maturation pathways for E. coli tRNA precursors: a random multienzyme process in vivo.
tRNA maturation consists of the specific removal of precursor sequences from both the 5' and 3' termini of an initial RNA transcript. How this is accomplished has heretofore not been ascertained in any system. Using Northern analysis of RNA isolated from a variety of RNase-deficient E. coli strains, we have identified the processing intermediates that accumulate in the absence of specific processing nucleases. From this information we have established the maturation pathways for 12 different E. coli tRNAs including the specific role of each of the relevant RNases in the process. The surprising conclusion from this work is that tRNA maturation is a stochastic process that lacks a defined order and that can proceed with a variety of alternative 3' processing nucleases.
Base Sequence↗
The mouse DNA binding protein Rc for the kappa B motif of transcription and for the V(D)J recombination signal sequences contains composite DNA-protein interaction domains and belongs to a new family of large transcriptional proteins.
Rc is a DNA binding protein with dual specificities for the V(D)J recombination signal sequences and for the B motif of the immunoglobulin kappa chain gene enhancer. The largest Rc transcript present in lymphoid cells/tissues is approximately 9 kb. Molecular cloning and sequence determination for 8822 bp of mouse Rc cDNA revealed an open reading frame of 2282 amino acids and long 5'- and 3'-untranslated regions. The derived amino acid sequence contains multiple DNA and protein interaction domains. Composite ZAS structures with tandem zinc fingers, an acidic motif, and a Ser/Thr-rich segment are located near the N-terminal and the C-terminal regions. The middle region of Rc contains a lone zinc finger, an acidic motif, a Ser-rich region, a nucleus localization signal, and GTPase motifs. Cloning and characterization of a mouse Rc gene show that the Rc cDNA corresponds to seven exons located in a genomic region spanning 70 kb. Exon 2 is exceptionally large, with 5487 bp. cDNA cloning and Northern blot analyses revealed multiple Rc transcripts, probably generated by alternative splicings. Sequence comparisons show that Rc belongs to a ZAS protein family that is involved in gene transcription and/or DNA recombination. The major histocompatibility complex class I gene enhancer binding proteins MBP1 and MBP2 are other representatives of this ZAS protein family.
Amino Acid Sequence↗
Interleukin-10 inhibits tumor metastasis through an NK cell-dependent mechanism.
Interleukin-10 (IL-10) is a recently described pleiotropic cytokine secreted mainly by type 2 helper T cells. Previous studies have shown that IL-10 suppresses cytokine expression by natural killer (NK) and type 1 T cells, thus down-regulating cell-mediated immunity and stimulating humoral responses. We here report that injected IL-10 protein is an efficient inhibitor of tumor metastasis in experimental (B16-F10) and spontaneous (M27 and Lox human melanoma) metastasis models in vivo at doses that do not have toxic effects on normal or cancer cells. Histological characterization after IL-10 treatment confirmed the absence of CD8+ and CD4+ T cells and macrophages at the sites of tumor growth, but abundant NK cells were localized at these sites. This unexpected finding was confirmed by showing that IL-10 inhibits most B16-F10 and Lox metastases in mice deficient in T or B cells (SCID and nu/nu mice), but not in those deficient in NK cells (beige mice or NK cell-depleted mice). However, IL-10 downregulation of pro-inflammatory cytokine production and/or recruitment of additional effector cells may also be involved in the anti-tumor effect at higher local concentrations of IL-10, since transfected B16 tumor cells expressing high amounts of IL-10 were rejected by normal, nu/nu, or SCID mice at the primary tumor stage, and there was still a 33% inhibition of tumor metastasis in beige mice.
Animals↗
Characterization of the structure and function of a new mitogen-activated protein kinase (p38beta).
Mitogen-activated protein (MAP) kinase cascades represent one of the major signal systems used by eukaryotic cells to transduce extracellular signals into cellular responses. Four MAP kinase subgroups have been identified in humans: ERK, JNK (SAPK), ERK5 (BMK), and p38. Here we characterize a new MAP kinase, p38beta. p38beta is a 372-amino acid protein most closely related to p38. It contains a TGY dual phosphorylation site, which is required for its kinase activity. Like p38, p38beta is activated by proinflammatory cytokines and environmental stress. A comparison of events associated with the activation of p38beta and p38 revealed differences, most notably in the preferred activation of p38beta by MAP kinase kinase 6 (MKK6), whereas p38 was activated nearly equally by MKK3, MKK4, and MKK6. Moreover, in vitro and in vivo experiments showed a strong substrate preference by p38beta for activating transcription factor 2 (ATF2). Enhancement of ATF2-dependent gene expression by p38beta was approximately20-fold greater than that of p38 and other MAP kinases tested. The data reported here suggest that while closely related, p38beta and p38 may be regulated by differing mechanisms and may exert their actions on separate downstream targets.
Activating Transcription Factor 2↗
Angular Distribution for the 7Be(d,n)8B Reaction at Ec.m.=5.8 MeV and the S17(0) Factor for the 7Be(p, gamma )8B Reaction.
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Journal Article↗
Analysis of phosphorylation and mutation of tyrosine residues of calmodulin on its activation of the erythrocyte Ca(2+)-transporting ATPase.
The role played by the phosphorylation sites of calmodulin on its ability to activate the human erythrocyte Ca(2+)-transporting ATPase (Ca(2+)-ATPase) was evaluated. Phosphorylation of mammalian calmodulin on serine/threonine residues by casein kinase II decreased its affinity for Ca(2+)-ATPase by twofold. In contrast, tyrosine phosphorylation of mammalian calmodulin by the insulin-receptor kinase did not significantly alter calmodulin-stimulated Ca(2+)-ATPase activity. Two variant calmodulins, each containing only one tyrosine residue (the second Tyr is replaced by Phe) were also examined: [F138]calmodulin, a mutant containing tyrosine at position 99, and wheat germ calmodulin which has tyrosine at position 139. The concentrations of [F138]calmodulin and wheat germ calmodulin required for half-maximal activation of Ca(2+)-ATPase were tenfold and fourfold higher, respectively, than mammalian calmodulin. Phosphorylation at Tyr99 of [F138]calmodulin shifted its affinity for Ca(2+)-ATPase towards that of mammalian calmodulin. However, phosphorylation at Tyr139 of wheat germ calmodulin had essentially no effect on its interaction with Ca(2+)-ATPase. Thus, all of the observed effects of both phosphorylation and substitution of residues of calmodulin are on its affinity for Ca(2+)-ATPase, not on Vmax. The effects are dependent on the site of phosphate incorporation. Replacement of tyrosine with phenylalanine has a larger effect than phosphorylation of tyrosine, suggesting that the observed functional alterations reflect a secondary conformational change in the C-terminal half of calmodulin, the region that is important in its activation of Ca(2+)-ATPase.
Animals↗
Laminin promotes differentiation of NB4 promyelocytic leukemia cells with all-trans retinoic acid.
The promyelocytic leukemia cell line, NB4, carries the t(15; 17) translocation and undergoes limited maturation in response to differentiation agents. Growth on laminin enhanced the ability of all-trans retinoic acid (ATRA) to promote morphologic maturation of these cells. Although exposure to ATRA in suspension yielded minimal maturation beyond the myelocyte stage, after 72 hours of exposure to ATRA on laminin the cells acquired the histologic appearance of metamyelocytes, band forms, and segmented neutrophils. After 96 hours, some cells acquired a spindle shape and became tightly adherent. Growth on collagen types I, III, IV, or fibronectin did not have this effect, although some cells did adhere to fibronectin. NB4 cells treated with ATRA in suspension or on laminin acquired the equivalent ability to reduce nitroblue tetrazolium or cytochrome C. Despite the improved morphologic maturation on laminin, the cells did not express secondary granule proteins such as lactoferrin or neutrophil collagenase. In addition, growth on laminin abolished cell proliferation in the presence of ionomycin. Growth on laminin and/or with ATRA induced new expression of alpha 6 integrin, a laminin receptor, as assessed by reverse transcription-polymerase chain reaction. Different conditions of growth (laminin or differentiation agent) resulted in specific patterns of expression of the alpha 6A and alpha 6B isoforms. Treatment with ATRA also resulted in the acquisition of high-level surface expression of alpha 6 integrin, as assessed by flow cytometry. Thus, treatment of NB4 promyelocytic leukemia cells with ATRA induced expression of alpha 6 integrin (a laminin receptor alpha-chain) and enabled more advanced maturation when the cells were grown on the extracellular matrix component, laminin, compared with tissue culture plastic.
Antigens, CD↗
Molecular cloning and sequence analysis of a cDNA encoding a cysteine proteinase inhibitor from Sorghum bicolor seedlings.
A 711-bp cDNA encoding a cysteine proteinase inhibitor (cystatin) was isolated from a cDNA library prepared from 7-10 cm Sorghum bicolor seedlings. The nearly full-length cDNA clone encodes 130 amino acid residues, which include the Gin-Val-Val-Ala-Gly motif, conserved among most of the known cystatins as a probable binding site for cysteine proteinases. The amino acid sequence of sorghum cystatin deduced from the cDNA clone shows significantly homology to those of other plant cystatins. The sorghum cystatin expressed in E. coli showed a strong papain-inhibitory activity.
Amino Acid Sequence↗
Genomic organization of the human SCN5A gene encoding the cardiac sodium channel.
The voltage-gated cardiac sodium channel, SCN5A, is responsible for the initial upstroke of the action potential. Mutations in the human SCN5A gene cause susceptibility to cardiac arrhythmias and sudden death in the long QT syndrome (LQT). In this report we characterize the genomic structure of SCN5A. SCN5A consists of 28 exons spanning approximately 80 kb on chromosome 3p21. We describe the sequences of all intron/exon boundaries and a dinucleotide repeat polymorphism in intron 16. Oligonucleotide primers based on exon-flanking sequences amplify all SCN5A exons by PCR. This work establishes the complete genomic organization of SCN5A and will enable high-resolution analyses of this locus for mutations associated with LQT and other phenotypes for which SCN5A may be a candidate gene.
Amino Acid Sequence↗
Band bending within inhomogeneously doped semiconductors with multilevel impurities. I. Theory.
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Journal Article↗
Band bending within inhomogeneously doped semiconductors with multilevel impurities. II. Examples.
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Journal Article↗
A theory of the visual motion coding in the primary visual cortex.
This paper demonstrates that much of visual motion coding in the primary visual cortex can be understood from a theory of efficient motion coding in a multiscale representation. The theory predicts that cortical cells can have a spectrum of directional indices, be tuned to different directions of motion, and have spatiotemporally separable or inseparable receptive fields (RF). The predictions also include the following correlations between motion coding and spatial, chromatic, and stereo codings: the preferred speed is greater when the cell receptive field size is larger, the color channel prefers lower speed than the luminance channel, and both the optimal speeds and the preferred directions of motion can be different for inputs from different eyes to the same neuron. These predictions agree with experimental observations. In addition, this theory makes predictions that have not been experimentally investigated systematically and provides a testing ground for an efficient multiscale coding framework. These predictions are as follows: (1) if nearby cortical cells of a given preferred orientation and scale prefer opposite directions of motion and have a quadrature RF phase relationship with each other, then they will have the same directional index, (2) a single neuron can have different optimal motion speeds for opposite motion directions of monocular stimuli, and (3) a neuron's ocular dominance may change with motion direction if the neuron prefers opposite directions for inputs from different eyes.
Color Perception↗
Cardiovascular lesions and skeletal myopathy in mice lacking desmin.
In order to further our understanding of the biological role of desmin, the muscle-specific intermediate filament protein, a null mutation in the desmin gene was introduced into the germ line of mice. Despite the complete lack of desmin, these mice developed and reproduced. Since we show that skeletal, cardiac, and smooth muscles form in the Des-/- mice, it is reasonable to propose that desmin is not essential for myogenic commitment or for myoblast fusion or differentiation in vivo. However, morphological abnormalities were observed in the diaphragm of adult mice; these were demonstrated by disorganized, distended, and nonaligned fibers. The heart presented areas of hemorrhaging in which fibrosis and ischemia were observed. We have also shown that the absence of desmin produces specific defects in smooth muscles. In conclusion, our results have demonstrated that desmin is not required for the differentiation of skeletal, cardiac, and smooth muscles but is essential to strengthen and maintain the integrity of these tissues.
Animals↗
Characterization of two glycolipid: alpha 2-3sialyltransferases, SAT-3 (CMP-NeuAc:nLcOse4Cer alpha 2-3sialyltransferase) and SAT-4 (CMP-NeuAc:GgOse4Cer alpha 2-3sialyltransferase), from human colon carcinoma (Colo 205) cell line.
Sialyltransferase activities, SAT-3 (CMP-NeuAc:nLcOse4Cer alpha 2-3sialyltransferase) and SAT-4 (CMP-NeuAc:GgOse4Cer alpha 2-3sialyltransferase), in Colo 205 cells catalyze the transfer of sialic acid to the terminal galactose of GlcNc-- and GalNAc-containing glycolipid substrates, respectively. Competition kinetic studies with nLcOse4Cer and GM1 as substrates in a sialyltransferase assay show that these two activities are catalyzed by two different catalytic entities. The two enzymes were co-solubilized with taurochlorate and resolved by DEAE--Cibacron Blue--Sepharose column chromatography into two elution peaks. The column eluent with SAT-3 activity failed to transfer sialic acid to asialo alpha(1)-acid glycoprotein, indicating that this enzyme is different from the sialyltransferase (ST3N) that synthesizes NeuAc alpha 2-3Gal linkage in asparagine-linked oligosaccharides of glycoprotein. However, SAT-3 activity can be immunoprecipitated with a polyclonal antibody produced against a protein expressed in Escherichia coli as GST-fusion protein from an ECB cDNA homolog of an alpha 2-3 sialyltransferase SAT-3 or STZ) the has been cloned from human melanoma cell and human placenta. Thus a concentration-dependent decrease in the residual SAT-3 activity relative to SAT-4 activity was observed in the supernatant after precipitation of the immune complex. Expression of SAT-3 (STZ) cDNA was also detected in Colo 205 cell by RT-PCR, followed by sequence analysis of the RT-PCR product. Characterization of the catalytic reaction products of SAT-3 and SAT-4 with thin-layer chromatography, sialidase treatment, and binding to specific antibodies indicates that both SAT-3 and SAT-4 catalyze the formation of alpha 2-3 linkage between sialic acid and terminal galactose of glycolipid substrates.
Base Sequence↗
The role of the carboxyl-terminal amino acid residues in Escherichia coli DNA topoisomerase III-mediated catalysis.
The role that the carboxyl-terminal amino acids of Escherichia coli DNA topoisomerase I (Topo I) and III (Topo III) play in catalysis was examined by comparing the properties of Topo III with those of a truncated enzyme lacking the generalized DNA binding domain of Topo III, Topo I, and a hybrid topoisomerase polypeptide containing the amino-terminal 605 amino acids of Topo III and the putative generalized DNA binding domain of Topo I. The deletion of the carboxyl-terminal 49 amino acids of Topo III decreases the affinity of the enzyme for its substrate, single-stranded DNA, by approximately 2 orders of magnitude and reduces Topo III-catalyzed relaxation of supercoiled DNA and Topo III-catalyzed resolution of DNA replication intermediates to a similar extent. Fusion of the carboxyl-terminal 312 amino acid residues of Topo I onto the truncated molecule stimulates topoisomerase-catalyzed relaxation 15-20-fold, to a level comparable with that of full-length Topo III. However, topoisomerase-catalyzed resolution of DNA replication intermediates was only stimulated 2-3-fold. Therefore, the carboxyl-terminal amino acids of these topoisomerases constitute a distinct and separable domain, and this domain is intimately involved in determining the catalytic properties of these polypeptides.
Amino Acid Sequence↗
Effects of nucleotide substitutions within the T-loop of precursor tRNAs on interaction with ATP/CTP:tRNA nucleotidyltransferases from Escherichia coli and yeast.
Recognition of tRNA and tRNA-like substrates by the enzyme ATP/CTP:tRNA nucleotidyltransferase requires chemically intact nucleotides within the T-loop, especially at positions 57 and 58, which are invariant purines among naturally occurring tRNAs. To test the effects of base substitutions at these positions, which are distant from the site of catalysis, we synthesized mutant tRNA(Glu) molecules. These in vitro-synthesized RNAs also contained an extra 33 bases at the 5' end and lacked post-transcriptionally modified bases. The precursor tRNAs were used as substrates for nucleotidyltransferases from Escherichia coli and yeast. Substitution of cytidines at either position 57 or 58 had dramatic inhibitory effects on recognition by both enzymes, including raising the apparent Km and lowering the apparent Vmax.; substitution of an adenosine at position 57 or a uridine at position 58 inhibited the reaction only slightly by comparison. Our results demonstrate that the identities of nucleotides at positions 57 and 58 are relevant to recognition by nucleotidyltransferase, and that a purine is required at position 57. The extra bases at the 5' end and the lack of post-transcriptionally modified bases did not substantially inhibit interaction with the enzyme, as judged by the wild-type precursor tRNA(Glu) acting as an effective substrate for both enzymes in the presence of equal concentrations of appropriate tRNA substrates isolated from E. coli.
Adenosine Triphosphate↗