The effects of protein intake on blood pressure and cardiovascular disease

PURPOSE OF REVIEW: Investigators, especially those from western countries, have commonly assumed that there is either no association or a direct association of protein intake with elevated blood pressure and atherosclerosis. In contrast, recent observational studies and clinical trials have suggested that increased protein intake, particularly protein from plant sources, might actually reduce blood pressure and prevent cardiovascular disease. RECENT FINDINGS: In epidemiological studies, an increased intake of protein has been associated with lower blood pressure and an attenuated increase in blood pressure over time. Furthermore, such studies also suggest that the beneficial effects of increased protein intake result from an increased consumption of protein from plant rather than animal sources. In several predominantly small trials, an increased intake of soy protein lowered blood pressure. With respect to clinical outcomes, reports from large cohort studies suggest that increased protein intake is associated with a reduced risk of ischemic heart disease and perhaps intraparenchymal hemorrhage. In other reports, a higher protein intake is one characteristic of a dietary pattern associated with a reduced risk of ischemic heart disease. The mechanisms by which protein could exert its beneficial effects include an increased intake of biologically active amino acids, peptides, or highly correlated nutrients. SUMMARY: Recent evidence suggests that an increased intake of protein, particularly plant protein, may lower blood pressure and reduce the risk of cardiovascular disease. However, the data are not sufficiently compelling to advocate an increased consumption of protein.     

Identification of recombinant AtPYL2, an abscisic acid receptor,in E. coli using a substrate-derived bioactive small molecule,a biotin linker with alkyne and amino groups,and a protein cross-linker

Target protein identification of bioactive small molecules is one of the most important research in forward chemical genetics. The affinity chromatography technique to use a resin bound with a small molecule is often used for identification of a target protein of a bioactive small molecule. Here we report a new method to isolate a protein targeted with a bioactive small molecule using a biotin linker with alkyne and amino groups, protein cross-linker containing disulfide bond, and a bioactive small molecule with an azido group (azido probe). After an azido probe is associated with a target protein, the complex of a target protein and azido probe is covalently bound through the biotin linker by azide-alkyne Huisgen cycloaddition and protein cross-linker containing disulfide bond. This ternary complex is immobilized on an affinity matrix with streptavidin, and then the target protein is selectively eluted with a buffer containing a reducing agent for cleavage of disulfide bonds. This method uses a probe having an azido group, which a small functional group, and has the possibility to be a solution strategy to overcome the hindrance of a functional group introduced into the probe that reduces association a target protein. The effectiveness of the method in this study was shown using linker 1, 3′-azidoabscisic acid 3, and protein cross-linker containing a disulfide bond (DTSSP 5).     

Quantitative filtration-blotting of protein in the presence of sodium dodecyl sulfate and its use for protein assay

It is thought that sodium dodecyl sulfate (SDS), an anionic detergent, binds to hydrophobic moieties of peptide to destroy the conformational structure of protein. Because of this property, it is involved in many biochemical procedures such as separations of protein and proteolytic digestion. In the course of our study on a solid-phase protein assay, we found that SDS acts as an effective reagent for protein blotting onto a hydrophobic membrane of polyvinylidene difluoride with a manifold dot-blot apparatus. At least 0.1% SDS in an acid-ethanol blotting solution, while reducing the bias of pronounced interferers for protein assay to protein-membrane interaction, quantitatively retains protein on the membrane. Presumably, protein denatures by SDS to become an unfolded state and adsorbs into the membrane by hydrophobic interaction, even in the presence of excess SDS. Therefore, bolts stained with a pyrogallol red-molybdate complex (Pyromolex) reagent unreactive to the membrane allowed a precise protein determination without significant interference of materials, especially detergents in the sample solution. The filtration-blotting with SDS would be a crucial procedure for quantitative analyses such as immunoblotting in detergent-containing samples, together with the solid-phase protein assay with limited sample volumes, such as 20 microL or less.     

Entry from the cell surface of severe acute respiratory syndrome coronavirus with cleaved S protein as revealed by pseudotype virus bearing cleaved S protein

Severe acute respiratory syndrome (SARS) coronavirus (SARS-CoV) is known to take an endosomal pathway for cell entry; however, it is thought to enter directly from the cell surface when a receptor-bound virion spike (S) protein is affected by trypsin, which induces cleavage of the S protein and activates its fusion potential. This suggests that SARS-CoV bearing a cleaved form of the S protein can enter cells directly from the cell surface without trypsin treatment. To explore this possibility, we introduced a furin-like cleavage sequence in the S protein at amino acids 798 to 801 and found that the mutated S protein was cleaved and induced cell fusion without trypsin treatment when expressed on the cell surface. Furthermore, a pseudotype virus bearing a cleaved S protein was revealed to infect cells in the presence of a lysosomotropic agent as well as a protease inhibitor, both of which are known to block SARS-CoV infection via an endosome, whereas the infection of pseudotypes with an uncleaved, wild-type S protein was blocked by these agents. A heptad repeat peptide, derived from a SARS-CoV S protein that is known to efficiently block infections from the cell surface, blocked the infection by a pseudotype with a cleaved S protein but not that with an uncleaved S protein. Those results indicate that SARS-CoV with a cleaved S protein is able to enter cells directly from the cell surface and agree with the previous observation of the protease-mediated cell surface entry of SARS-CoV.     

Site-specific, covalent attachment of proteins to a solid surface

Immobilized and site-specifically labeled proteins are becoming invaluable tools in proteomics. Here, we describe a strategy to attach a desired protein to a solid surface in a covalent, site-specific manner. This approach employs an enzymatic posttranslational modification method to site-specifically label a target protein with an azide; an alternative substrate for protein farnesyl transferase containing an azide group was developed for this purpose. A bio-orthogonal Cu(I)-catalyzed cycloaddition reaction is then used to covalently attach the protein to agarose beads bearing an alkyne functional group. We demonstrate that both the azide incorporation and the capture steps can be performed on either a purified protein target or on a protein present within a complex mixture. This approach involves the use of a four-residue tag which is significantly smaller than most other tags reported to date and results in covalent immobilization of the target protein. Hence it should have significant applicability in protein science.     

Identification and characterization of a novel Golgi protein, golgin-67

In the course of screening a lambdagt11 human leukemic T-cell cDNA expression library with an antibody specific to the mitotic target of Src, Sam68, we identified and cloned a cDNA encoding a novel protein with a predicted molecular mass of 51.4 kDa. Polyclonal antibodies raised to a His(6)-tagged construct of this protein, detected a approximately 67-kDa protein in immunoprecipitation experiments, and cytological studies showed that this protein localized to the Golgi complex, through colocalization experiments with specific Golgi markers. Therefore, we designated this protein golgin-67. Sequence analysis revealed that golgin-67 is a highly coiled-coil protein, with potential Cdc2 and Src kinase phosphorylation motifs. It has sequence homologies to other Golgi proteins, including the coatamer complex I vesicle docking protein, GM130. Structurally, golgin-67 resembles, golgin-84, an integral membrane Golgi protein with an N-terminal coiled-coil domain and a single C-terminal transmembrane domain. The C-terminal region of golgin-67, which contains a predicted transmembrane domain, was demonstrated to be essential for its Golgi localization.     

Agonist-induced phosphorylation of an immunologically ras-related protein in human erythroleukemia cells

Monoclonal antibody M90 recognizes a specific epitope of the ras-encoded p21 protein. This region comprises amino acids 107-130 containing the residues 116-119, which are related to GTP binding. This antibody strongly reacts on Western Blots with a 22kDa protein from human erythroleukemia (HEL) cells. Treatment of HEL cells with iloprost, an agonist that increases cellular cyclic AMP levels, produces the appearance of a protein with an apparent molecular mass of 24kDa. This protein is also recognized by antiserum M90 on Western Blots; its appearance parallels a decrease of the 22kDa protein, and it can be labeled with 32P. This effect is also observed with dibutyryl cyclic AMP, which indicates phosphorylation of the 22kDa protein by cyclic AMP-dependent protein kinase. This phosphorylation produces an electrophoretic mobility change of the 22kDa protein to a 24kDa region on gels. The change of mobility of the 22kDa protein induced by iloprost in HEL cells is also observed when the protein is labeled with [35S]methionine and immunoprecipitated with antiserum M90. This information indicates a coupling mechanism involving phosphorylation of an oncogene product in HEL cells.     

Microinjection of antibodies to a 62 kd mitotic apparatus protein arrests mitosis in dividing sea urchin embryos

Previously, we described a 62 kd protein that is a component of the isolated sea urchin mitotic apparatus. This protein is a substrate for an endogenous, calcium/calmodulin-dependent protein kinase also associated with the mitotic apparatus. Phosphorylation of the 62 kd protein directly correlates with the depolymerization of microtubules in isolated mitotic apparatuses. Here we report a test of the function of the 62 kd protein in vivo. Double labeling studies using a monoclonal antibody to tubulin and an affinity purified antibody specific for the 62 kd protein reveal that the 62 kd protein co-localizes with mitotic apparatus microtubules. When affinity purified antibodies to the 62 kd protein were microinjected into dividing sea urchin embryos, mitosis was blocked in a stage-specific manner. The results are discussed with respect to the role of the 62 kd protein in the metaphase-anaphase transition.     

The Saccharomyces cerevisiae CKS1 gene, a homolog of the Schizosaccharomyces pombe suc1+ gene, encodes a subunit of the Cdc28 protein kinase complex.

The Saccharomyces cerevisiae gene CDC28 encodes a protein kinase required for cell cycle initiation. In an attempt to identify genes encoding proteins that interact with the Cdc28 protein kinase, high-copy plasmid suppressors of a temperature-sensitive cdc28 mutation were isolated. One such suppressor, CKS1, was found to encode an 18-kilodalton protein that shared a high degree of homology with the suc1+ protein (p13) of Schizosaccharomyces pombe (67% amino acid sequence identity). Disruption of the chromosomal CKS1 gene conferred a G1 arrest phenotype similar to that of cdc28 mutants. The presence of the 18-kilodalton Cks1 protein in yeast lysates was demonstrated by using Cks-1 specific antiserum. Furthermore, the Cks1 protein was shown to be physically associated with active forms of the Cdc28 protein kinase. These data suggest that Cks1 is an essential component of the Cdc28 protein kinase complex.     

Engineering FKBP-Based Destabilizing Domains to Build Sophisticated Protein Regulation Systems

Targeting protein stability with small molecules has emerged as an effective tool to control protein abundance in a fast, scalable and reversible manner. The technique involves tagging a protein of interest (POI) with a destabilizing domain (DD) specifically controlled by a small molecule. The successful construction of such fusion proteins may, however, be limited by functional interference of the DD epitope with electrostatic interactions required for full biological function of proteins. Another drawback of this approach is the remaining endogenous protein. Here, we combined the Cre-LoxP system with an advanced DD and generated a protein regulation system in which the loss of an endogenous protein, in our case the tumor suppressor PTEN, can be coupled directly with a conditionally fine-tunable DD-PTEN. This new system will consolidate and extend the use of DD-technology to control protein function precisely in living cells and animal models.     

Immunogenic protein MPB57 from Mycobacterium bovis BCG: molecular cloning, nucleotide sequence and expression

Using a single-probe method, we have cloned the gene for an immunogenic MPB57 protein of Mycobacterium bovis BCG. The nucleotide sequence includes an ORF of 300 base pairs encoding a protein of 99 amino acids with an Mr of 10,818. This cloned gene was expressed in an Escherichia coli expression vector to give a mature protein which reacted with a polyclonal antibody raised against MPB57.     

The acidity of protein fusion partners predominantly determines the efficacy to improve the solubility of the target proteins expressed in Escherichia coli

Maximization of the soluble protein expression in Escherichia coli (E. coli) via the fusion expression strategy is usually preferred for academic, industrial and pharmaceutical purposes. In this study, a set of distinct protein fusion partners were comparatively evaluated to promote the soluble expression of two target proteins including the bovine enterokinase largely prone to aggregation and the green fluorescent protein with moderate native solubility. Within protein attributes that are putatively involved in protein solubility, the protein acidity was of particular concern. Our results explicitly indicated the protein fusion partners with a stronger acidity remarkably exhibited a higher capacity to enhance the solubility of the target proteins. Among them, msyB, an E. coli acidic protein that suppresses the mutants lacking function of protein export, was revealed as an excellent protein fusion partner with the distinguished features including high potential to enhance protein solubility, efficient expression, relatively small size and the origin of E. coli itself. In principle, our results confirmed the modified solubility model of Wilkinson-Harrison and especially deepened understanding its essence. Meanwhile, the roles of other parameters such as protein hydrophilicity in solubility enhancement were discussed, a guideline to design or search an optimum protein solubility enhancer was also proposed.     

Newly Imported Rieske Iron-Sulfur Protein Associates with Both Cpn60 and Hsp70 in the Chloroplast Stroma

The precursor of the Rieske FeS protein, a thylakoid membrane protein, was imported by isolated pea chloroplasts, and the mature protein was shown to be integrated into the cytochrome bf complex of the thylakoid membranes. Insertion into the thylakoid membrane was sensitive to the ionophores nigericin and valinomycin, suggesting a requirement for a proton motive force. A considerable proportion of the imported Rieske protein was detected in the stromal fraction of the chloroplasts, and this increased when membrane insertion was blocked with ionophores. Electrophoresis of the stromal fraction under nondenaturing conditions resolved two distinct complexes containing the Rieske protein. One of these complexes was identified as an association of the Rieske protein with the chaperonin Cpn60 complex by its electrophoretic mobility, Mg-ATP-dependent dissociation, and immunoprecipitation with anti-Cpn60 antibodies. Coimmunoprecipitation of imported Rieske protein with anti-heat shock protein 70 (Hsp70) antibodies indicated that the Rieske protein was also associated, in an ATP-dissociable form, with a chloroplast Hsp70 homolog. Immunoprecipitation analysis of an import time course detected the highest amounts of the Cpn60-Rieske protein complex early in the time course, whereas highest amounts of the Hsp70-Rieske protein complex were formed much later. The disappearance of the Cpn60-Rieske protein complex correlated with increased amounts of the Rieske protein in the thylakoid fraction.     

Modulation of Ca2+-activated, phospholipid-dependent protein kinase in platelets treated with a tumor-promoting phorbol ester

Incubation of human platelets with 12-0-tetradecanoylphorbol-13-acetate (TPA) caused a rapid decrease in soluble Ca2+, phospholipid-dependent protein kinase activity (protein kinase C) and an increase in protein kinase C associated with the particulate fraction. TPA also induced an increased activity of a Ca2+, phospholipid-independent protein kinase activity in both the soluble and the particulate fractions of platelets. This latter kinase eluted from DEAE cellulose columns at a higher salt concentration than protein kinase C, and was shown by Sephadex G-100 chromatography to have a MW of approx. 50,000 compared with an MW of 80,000 for protein kinase C. The data suggest that TPA treatment of platelets causes irreversible activation of protein kinase C by proteolysis of the enzyme to a form active in the absence of Ca2+ and phospholipid.     

Spectroscopic, thermodynamic and kinetic properties of Candida nitratophila nitrate reductase.

HL-60 cells possess a 60 kDa Ca2(+)-binding protein that is contained in a discrete subcellular compartment, referred to as calciosomes. Subcellular fractionation studies have suggested that, in HL-60 cells, this intracellular compartment is an Ins(1,4,5)P3-sensitive Ca2+ store. In order to investigate the structural relationship of the 60 kDa Ca2(+)-binding protein of HL-60 cells to other Ca2(+)-binding proteins, we have purified the protein by ammonium sulphate extraction, acid precipitation, and DEAE-cellulose and phenyl-Sepharose column chromatography. The N-terminal sequence of the protein shows 93% identity with rabbit muscle calreticulin, a recently cloned sarcoplasmic reticulum Ca2(+)-binding protein. No amino acid sequence similarity with calsequestrin was found, although the purified protein cross-reacted with anti-calsequestrin antibodies. The calreticulin-related protein of HL-60 cells might play a role as an intravesicular Ca2(+)-binding protein of an Ins(1,4,5)P3-sensitive Ca2+ store.     

Biochemical basis of the constitutive repressor cleavage activity of recA730 protein. A comparison to recA441 and recA803 proteins.

The recA730 mutation results in constitutive SOS and prophage induction. We examined biochemical properties of recA730 protein in an effort to explain the constitutive activity observed in recA730 strains. We find that recA730 protein is more proficient than the wild-type recA protein in the competition with single-stranded DNA binding protein (SSB protein) for single-stranded DNA (ssDNA) binding sites. Because an increased aptitude in the competition with SSB protein has been previously reported for recA441 protein and recA803 protein, we directly compared their in vitro activities with those of recA730 protein. At low magnesium ion concentration, both ATP hydrolysis and lexA protein cleavage experiments demonstrate that these recA proteins displace SSB protein from ssDNA in a manner consistent with their in vivo repressor cleavage activity, i.e. recA730 protein > recA441 protein > recA803 protein > recAwt protein. Additionally, a correlation exists between the proficiency of the recA proteins in SSB protein displacement and their rate of association with ssDNA. We propose that an increased rate of association with ssDNA allows recA730 protein to displace SSB protein from the ssDNA that occurs naturally in Escherichia coli and thereby to become activated for the repressor cleavage that leads to SOS induction. RecA441 protein is similarly activated for repressor cleavage; however, in this case, significant SSB protein displacement occurs only at elevated temperature. At physiological magnesium ion concentration, we argue that recA803 protein and wild-type recA protein do not displace sufficient SSB protein from ssDNA to constitutively induce the SOS response.     

Hypoxic up-regulation of triosephosphate isomerase expression in mouse brain capillary endothelial cells

A protein with a molecular mass of 27kDa was induced by hypoxia in a mouse brain capillary endothelial cell line and identified as triosephosphate isomerase (TPI) by amino-terminal sequencing. Hypoxia caused an elevation of the TPI protein level, concomitant with an increase of the TPI mRNA level. However, hypoxia resulted in an insufficient elevation of TPI activity level, compared to an increase of TPI protein level. When cells expressing the recombinant TPI protein with histidine tag were exposed to hypoxia and the TPI protein was affinity-purified, the catalytic activity (specific activity) of the TPI protein purified from hypoxic cells was substantially lower than that obtained from normoxic cells. In addition, three TPI isoforms with an electrophoretic multiplicity were found; two of the three isoforms were substantially increased in response to the hypoxia, but the level of the most acidic isoform was barely changed. The induction of TPI gene expression by hypoxia was suppressed by (1) a chelator of intracellular Ca(2+), (2) a blocker of non-selective cation channels, (3) a blocker of Na(+)/Ca(2+) exchangers, (4) an inhibitor of Ca(2+)/calmodulin-dependent protein kinases, and (5) an inhibitor of c-jun/AP-1 activation.     

The functional motif of SARS-CoV S protein involved in the interaction with ACE2

SARS-CoV is a newly discovery pathogen causing severe acute respiratory problems. It has been established that the S protein in this pathogen plays an important rule in the adsorption and penetration of SARS-CoV into the host cell by interaction with the ACE2 receptor. To determinant which functional motif of the S protein was involved in the interaction with ACE2, seven truncated S proteins deleted from the N or C terminal were obtained by an E.coli expression system and purified by column chromatography to homogeneity. Each truncated S protein was fixed on to the well of an ELISA plate and an interaction was initiated with the ACE2 protein. The adsorption were quantified by ELISA, and the results indicated that amino acids from 388 to 496 of the S protein was responsible for the interaction with the ACE2 receptor, and the interaction could be completely disrupted by an antibody specific to these amino acids. Deletions adjacent to this domain did not appear to have a significant impact on the interaction with ACE2, suggesting that the S protein of SARS-CoV could be developed as a vaccine to prevent the spread of SARS-CoV.     

Association of the cytoplasmic membrane protein XpsN with the outer membrane protein XpsD in the type II protein secretion apparatus of Xanthomonas campestris pv. campestris

An xps gene cluster composed of 11 open reading frames is required for the type II protein secretion in Xanthomonas campestris pv. campestris. Immediately upstream of the xpsD gene, which encodes an outer membrane protein that serves as the secretion channel by forming multimers, there exists an open reading frame (previously designated ORF2) that could encode a protein of 261 amino acid residues. Its N-terminal hydrophobic region is a likely membrane-anchoring sequence. Antibody raised against this protein could detect in the wild-type strain of X. campestris pv. campestris a protein band with an apparent molecular mass of 36 kDa by Western blotting. Its aberrant slow migration in sodium dodecyl sulfate-polyacrylamide gels might be due to its high proline content. We designated this protein XpsN. By constructing a mutant strain with an in-frame deletion of the chromosomal xpsN gene, we demonstrated that it is required for the secretion of extracellular enzyme by X. campestris pv. campestris. Subcellular fractionation studies indicated that the XpsN protein was tightly associated with the membrane. Sucrose gradient sedimentation followed by immunoblot analysis revealed that it primarily appeared in the cytoplasmic membrane fractions. Immune precipitation experiments indicated that the XpsN protein was coprecipitated with the XpsD protein. In addition, the XpsN protein was co-eluted with the (His)(6)-tagged XpsD protein from the metal affinity chromatography column. All observations suggested that the XpsN protein forms a stable complex with the XpsD protein. In addition, immune precipitation analysis of the XpsN protein with various truncated XpsD proteins revealed that the C-terminal region of the XpsD protein between residues 650 and 759 was likely to be involved in complex formation between the two.     

Boost Protein Expression through Co-Expression of LEA-Like Peptide in Escherichia coli

The boost protein expression has been done successfully by simple co-expression with a late embryogenesis abundant (LEA)-like peptide in Escherichia coli. Frequently, overexpression of a recombinant protein fails to provide an adequate yield. In the study, we developed a simple and efficient system for overexpressing transgenic proteins in bacteria by co-expression with an LEA-like peptide. The design of this peptide was based on part of the primary structure of an LEA protein that is known hydrophilic protein to suppress aggregation of other protein molecules. In our system, the expression of the target protein was increased remarkably by co-expression with an LEA-like peptide consisting of only 11 amino acid residues. This could provide a practical method for producing recombinant proteins efficiently.