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PubMed1995

Xenopus oocytes as a heterologous expression system for plant proteins.

The Xenopus oocyte is a robust and convenient system for the transient expression of many different animal proteins and it has recently been demonstrated that oocytes can also translate, process, and target plant proteins. This expression system can also be used to clone genes, characterize function, and study posttranslational processing of proteins. Here we describe the methodology for the expression of plant proteins, in particular membrane proteins, in Xenopus oocytes.

Animals↗
PubMed1983

The frequency and distribution of methylatable DNA sequences in leguminous plant protein coding genes.

Methylation of higher plant DNA occurs at up to 25% of all cytosines, primarily in the sequences CpG2 and CpNpG, both of which are over 80% methylated in wheat and tobacco (Gruenbaum et al 1981). CpG and CpNpG frequencies and distributions in the known sequences of cloned genes of leguminous plants were analyzed. In this sample CpG occurred at only 49% of the frequency expected if the bases were distributed at random. This lower frequency may be attributed to the fixation of mutations generated by a high rate of deamination of 5methylcytosine to thymine (Salser 1977). Consistent with this hypothesis, the product of CpG transitions, TpG and CpA, were significantly above their expected frequency. However CpNpG occurred at approximately expected levels and there was no significant increase in its transition products CpNpA and TpNpG. Possible explanations for this phenomenon are discussed. An analysis of the distribution of di- and trinucleotides across functionally classified regions of genes showed CpG to be asymmetrically distributed. CpG was on average significantly enriched in the 3' flanking regions compared to other regions. This may reflect a methylation-mediated regulatory role for this region in some legume genes.

Base Sequence↗
PubMed1998

MP2C, a plant protein phosphatase 2C, functions as a negative regulator of mitogen-activated protein kinase pathways in yeast and plants.

By interference of the yeast pheromone mitogen-activated protein kinase (MAPK) pathway with an alfalfa cDNA expression library, we have isolated the MP2C gene encoding a functional protein phosphatase type 2C. Epistasis analysis in yeast indicated that the molecular target of the MP2C phosphatase is Ste11, a MAPK kinase kinase that is a central regulator of the pheromone and osmosensing pathways. In plants, MP2C functions as a negative regulator of the stress-activated MAPK (SAMK) pathway that is activated by cold, drought, touch, and wounding. Although activation of the SAMK pathway occurs by a posttranslational mechanism, de novo transcription and translation of protein factor(s) are necessary for its inactivation. MP2C is likely to be this or one of these factors, because wound-induced activation of SAMK is followed by MP2C gene expression and recombinant glutathione S-transferase-MP2C is able to inactivate extracts containing wound-induced SAMK. Wound-induced MP2C expression is a transient event and correlates with the refractory period, i.e., the time when restimulation of the SAMK pathway is not possible by a second stimulation. These data suggest that MP2C is part of a negative feedback mechanism that is responsible for resetting the SAMK cascade in plants.

Amino Acid Sequence↗
PubMed1984

Sodium chloride supplementation of all plant protein broiler diets.

Male broiler chicks were fed all plant protein diets with soybean meal or a mixture of soybean and canola meals as the source of supplementary protein from 0 to 4 weeks of age. Supplementation of the diets with .25% sodium chloride did not meet the requirements of the chicks for maximum growth. Growth was accelerated when the dietary sodium chloride concentration was increased to .50 and 1.00%.

Animals↗
PubMed1995

Inhibition of the integrase of human immunodeficiency virus (HIV) type 1 by anti-HIV plant proteins MAP30 and GAP31.

MAP30 (Momordica anti-HIV protein of 30 kDa) and GAP31 (Gelonium anti-HIV protein of 31 kDa) are anti-HIV plant proteins that we have identified, purified, and cloned from the medicinal plants Momordica charantia and Gelonium multiflorum. These antiviral agents are capable of inhibiting infection of HIV type 1 (HIV-1) in T lymphocytes and monocytes as well as replication of the virus in already-infected cells. They are not toxic to normal uninfected cells because they are unable to enter healthy cells. MAP30 and GAP31 also possess an N-glycosidase activity on 28S ribosomal RNA and a topological activity on plasmid and viral DNAs including HIV-1 long terminal repeats (LTRs). LTRs are essential sites for integration of viral DNA into the host genome by viral integrase. We therefore investigated the effect of MAP30 and GAP31 on HIV-1 integrase. We report that both of these antiviral agents exhibit dose-dependent inhibition of HIV-1 integrase. Inhibition was observed in all of the three specific reactions catalyzed by the integrase, namely, 3' processing (specific cleavage of the dinucleotide GT from the viral substrate), strand transfer (integration), and "disintegration" (the reversal of strand transfer). Inhibition was studied by using oligonucleotide substrates with sequences corresponding to the U3 and U5 regions of HIV LTR. In the presence of 20 ng of viral substrate, 50 ng of target substrate, and 4 microM integrase, total inhibition was achieved at equimolar concentrations of the integrase and the antiviral proteins, with EC50 values of about 1 microM. Integration of viral DNA into the host chromosome is a vital step in the replicative cycle of retroviruses, including the AIDS virus. The inhibition of HIV-1 integrase by MAP30 and GAP31 suggests that impediment of viral DNA integration may play a key role in the anti-HIV activity of these plant proteins.

Antiviral Agents↗
PubMed1992

Anti-Sm autoantibodies of systemic lupus erythematosus cross react with dietary plant proteins.

Cross reactivity of patient lupus autoantibodies to the small nuclear ribonucleoprotein particles of many different types of animals is well documented. The aim of our research was to determine if any level of cross reactivity existed between proteins of common dietary plants and anti-Sm autoantibodies of lupus patient's sera, as has been found for scleroderma patient sera (Agris et al., Exptl. Cell Res. 189, 276-279, 1990). Protein extracts from soy bean, corn, spinach, and carrot were analyzed. At least one protein (molecular weight approximately 28,000 daltons) common to all the above protein extracts was recognized by most of the anti-Sm sera tested. Affinity purified antibody eluted from the 28 kilodalton plant protein specifically recognized the Sm proteins of a HeLa cell protein extract. Recognition of the 28 kilodalton dietary plant protein was found to be unique to anti-Sm lupus sera.

Autoantibodies↗
PubMed1999

MAF1, a novel plant protein interacting with matrix attachment region binding protein MFP1, is located at the nuclear envelope.

The interaction of chromatin with the nuclear matrix via matrix attachment region (MAR) DNA is considered to be of fundamental importance for chromatin organization in all eukaryotic cells. MAR binding filament-like protein 1 (MFP1) from tomato is a novel plant protein that specifically binds to MAR DNA. Its filament protein-like structure makes it a likely candidate for a structural component of the nuclear matrix. MFP1 is located at nuclear matrix-associated, specklelike structures at the nuclear envelope. Here, we report the identification of a novel protein that specifically interacts with MFP1 in yeast two-hybrid and in vitro binding assays. MFP1 associated factor 1 (MAF1) is a small, soluble, serine/threonine-rich protein that is ubiquitously expressed and has no similarity to known proteins. MAF1, like MFP1, is located at the nuclear periphery and is a component of the nuclear matrix. These data suggest that MFP1 and MAF1 are in vivo interaction partners and that both proteins are components of a nuclear substructure, previously undescribed in plants, that connects the nuclear envelope and the internal nuclear matrix.

Amino Acid Sequence↗
PubMed1992

Anti-HIV plant proteins catalyze topological changes of DNA into inactive forms.

GAP 31, DAP 32 and DAP 30 comprise a new class of plant proteins with potent anti-HIV activity and insignificant cytotoxicity. We report here the identification and characterization of a new DNA enzyme activity in these three proteins. They irreversibly relax and decatenate supercoiled DNA, as well as catalyze double-stranded breakage to form linear DNA. The relaxed molecules are topologically inactive and no longer serve as substrates for DNA gyrase to form supercoils, phenomena similar to those of cellular topoisomerases in the presence of topoisomerase poisons. The ability of these anti-HIV agents to interrupt essential topological interconversions of DNA may provide a novel mechanism for their antiviral and antitumor actions. The presence of this new DNA topological enzyme activity in these plant proteins also suggests that their anti-HIV activity may not be merely a consequence of ribosome inactivation previously recognized.

Amino Acid Sequence↗
PubMed2003

A novel plant protein undergoing light-induced phosphorylation and release from the photosynthetic thylakoid membranes.

The characteristics of a phosphoprotein with a relative electrophoretic mobility of 12 kDa have been unknown during two decades of studies on redox-dependent protein phosphorylation in plant photosynthetic membranes. Digestion of this protein from spinach thylakoid membranes with trypsin and subsequent tandem nanospray-quadrupole-time-of-flight mass spectrometry of the peptides revealed a protein sequence that did not correspond to any previously known protein. Sequencing of the corresponding cDNA uncovered a gene for a precursor protein with a transit peptide followed by a strongly basic mature protein with a molecular mass of 8,640 Da. Genes encoding homologous proteins were found on chromosome 3 of Arabidopsis and rice as well as in ESTs from 20 different plant species, but not from any other organisms. The protein can be released from the membrane with high salt and is also partially released in response to light-induced phosphorylation of thylakoids, in contrast to all other known thylakoid phosphoproteins, which are integral to the membrane. On the basis of its properties, this plant-specific protein is named thylakoid soluble phosphoprotein of 9 kDa (TSP9). Mass spectrometric analyses revealed the existence of non-, mono-, di-, and triphosphorylated forms of TSP9 and phosphorylation of three distinct threonine residues in the central part of the protein. The phosphorylation and release of TSP9 from the photosynthetic membrane on illumination favor participation of this basic protein in cell signaling and regulation of plant gene expression in response to changing light conditions.

Amino Acid Sequence↗
PubMed1994

Mammalian AMP-activated protein kinase is homologous to yeast and plant protein kinases involved in the regulation of carbon metabolism.

In mammals, an AMP-activated protein kinase (AMPK) phosphorylates both acetyl-CoA carboxylase and 3-hydroxy-3-methylglutaryl-CoA reductase in vitro and has been proposed to play a major role in the regulation of lipid metabolism in vivo. We report here the primary sequence of rat AMPK and show that antibodies raised against synthetic peptides based on the deduced sequence of AMPK immunoprecipitate AMPK activity from rat liver extracts. AMPK has a remarkable degree of sequence identity to the proteins encoded by the yeast SNF1 gene and the plant RKIN1 gene. SNF1 protein kinase activity is essential for release of genes from glucose repression in Saccharomyces cerevisiae. Expression of cRKIN1 in yeast snf1 mutants restores SNF1 function. These results indicate that AMPK, SNF1, and RKIN1 form part of a family of protein kinases that have been highly conserved throughout evolution. Our results suggest that AMPK may be involved in the regulation of a wide range of metabolic pathways.

AMP-Activated Protein Kinases↗
PubMed1982

Effect of plant proteins on cholesterol metabolism in growing rats fed atherogenic diets.

Weanling rats were fed atherogenic diets containing 2% cholesterol and 0.5% bile acids for 4 weeks. The experimental diets contained 10% protein derived from soy protein, wheat gluten, or wheat gluten supplemented with lysine and threonine. The control diet contained 10% protein derived from casein. Rats fed the plant proteins were found to have lower serum cholesterol and triglyceride levels, no detectable amounts of low density lipoprotein, a smaller amount of very low density lipoprotein and a higher concentration of high density lipoprotein (HDL) as compared to the control animals. There were no differences in the serum HDL-cholesterol level between the control and the experimental groups. It was shown that the hypocholesterolemic effect of wheat gluten is independent of the low lysine concentration or the ratio of lysine/arginine in it.

Animals↗
PubMed2004

PHYTOPROT: a database of clusters of plant proteins.

All the protein sequences from plants (including Arabidopsis thaliana) available from SwissProt/TrEMBL have been the subject of an all-by-all systematic comparison and grouped into clusters of related proteins. Within each cluster, the sequences have been submitted to pyramidal classification; in the case where two or several subfamilies have been grouped together, the pyramidal tree helps in finding which sequences make the links between subfamilies. In addition, the 'domains' that are common to two or more sequences within a cluster were determined and displayed à la ProDom. The resulting graphical representations proved to be quite efficient in pinpointing those protein sequences suffering from a probable error in the annotation of their genes. The clusters can be searched through various criteria and their pyramidal classifications and their domain representations can be displayed by querying http://genoplante-info. infobiogen.fr/phytoprot. The user can also launch a BLAST search of a query sequence against all the clusters.

Arabidopsis Proteins↗
PubMed1981

Primary structure of the hydrophobic plant protein crambin.

Crambin, a hydrophobic plant seed protein, consists of a single chain of 46 amino acids with a calculated molecular weight of 4720. The primary structure was determined by using solid-phase sequencing techniques and was confirmed through X-ray crystallographic analysis of the protein at 1.5-A resolution [Hendrickson, W. A., & Teeter, M. M. (1981) Nature (London) 290, 107-112]. High-performance liquid chromatographic separation of the proteolytic fragments from crambin led to the identification of two sites of microheterogeneity. The three disulfide bonds were located at positions 3-40, 4-32, and 16-26 from the crystallographic data. Comparison of the primary structure with known sequences revealed that crambin is homologous with the plant toxins purothionin and viscotoxin. Methods to estimate protein secondary structure were applied and found to predict all of crambin's structure except its amphiphilic helix.

Amino Acid Sequence↗
PubMed2004

A technology platform for the fast production of monoclonal recombinant antibodies against plant proteins and peptides.

The application of recombinant antibodies in plant biology research is limited because plant researchers have minimal access to high-quality phage display libraries. Therefore, we constructed a library of 1.3 x 10(10) clones displaying human single-chain variable fragments (scFvs) that is available to the academic community. The scFvs selected from the library against a diverse set of plant proteins showed moderate to high antigen-binding affinity together with high specificity. Moreover, to optimize an scFv as immunodetection agent, two expression systems that allow efficient production and purification of bivalent scFv-Fc and scFv-CkappaZIP fusion proteins were integrated. We are convinced that this antibody platform will further stimulate applications of recombinant antibodies such as the diagnostic detection or immunomodulation of specific antigens in plants.

Antibodies, Monoclonal↗
PubMed2006

The structure of Rauvolfia serpentina strictosidine synthase is a novel six-bladed beta-propeller fold in plant proteins.

The enzyme strictosidine synthase (STR1) from the Indian medicinal plant Rauvolfia serpentina is of primary importance for the biosynthetic pathway of the indole alkaloid ajmaline. Moreover, STR1 initiates all biosynthetic pathways leading to the entire monoterpenoid indole alkaloid family representing an enormous structural variety of approximately 2000 compounds in higher plants. The crystal structures of STR1 in complex with its natural substrates tryptamine and secologanin provide structural understanding of the observed substrate preference and identify residues lining the active site surface that contact the substrates. STR1 catalyzes a Pictet-Spengler-type reaction and represents a novel six-bladed beta-propeller fold in plant proteins. Structure-based sequence alignment revealed a common repetitive sequence motif (three hydrophobic residues are followed by a small residue and a hydrophilic residue), indicating a possible evolutionary relationship between STR1 and several sequence-unrelated six-bladed beta-propeller structures. Structural analysis and site-directed mutagenesis experiments demonstrate the essential role of Glu-309 in catalysis. The data will aid in deciphering the details of the reaction mechanism of STR1 as well as other members of this enzyme family.

Amino Acid Sequence↗
PubMed1983

The immunomodulatory activity of the plant proteins Momordica charantia inhibitor and pokeweed antiviral protein.

The immunological activity of Momordica Charantia inhibitor (MCI) and of Pokeweed antiviral protein (PAP-S), 30,000 daltons plant proteins possessing close similarity to Ricin A chain as inhibitor of protein synthesis, was investigated in mice. In vivo, single nontoxic injections of microgram amount of these substances delayed H2-incompatible skin allograft rejection, splenocyte responsiveness to ConA and PHA, but not to LPS, and abrogated the PFC response to a T-dependent (SRBC) antigen while totally sparing that to a T-independent (S III) stimulus. Injection of these substances could also reduce NK cell activity while increasing macrophage-mediated spontaneous cytotoxicity. In vitro, MCI and PAP-S at non-cytotoxic concentrations inhibited lymphoid cell responsiveness to PHA and ConA, but not to LPS, and markedly enhanced macrophage-dependent cytotoxicity.

Animals↗
PubMed1991

A method for extraction and 2-D gel electrophoresis of plant proteins with selective isoelectric points.

A procedure for extracting and separating plant proteins by isoelectric point and 2-dimensional gel electrophoresis (2-DGE) is presented. Resolution of basic proteins using nonequilibrium pH gradient electrophoresis (NEPHGE) increased when run without the presence of acidic proteins. Isoelectric focusing without basic proteins favored the migration of the acidic and the more neutrally charged proteins into tube gels. Without the basic groups, negatively charged proteins could be focused for 20 h and longer without consideration of cathodic drift effects. The procedure facilitates gel analysis by simplifying the protein pattern on second dimension gels. Another advantage is that greater relative amounts of any class of proteins can be electrophoresed in the first dimension gels.

Electrophoresis, Gel, Two-Dimensional↗