Identification of sialic acid-rich glycoproteins on polyacrylamide gels

Identification of ferredoxin II as a major calcium binding protein in the nitrogen-fixing symbiotic bacterium Mesorhizobium loti

BACKGROUND

Legumes establish with rhizobial bacteria a nitrogen-fixing symbiosis which is of the utmost importance for both plant nutrition and a sustainable agriculture. Calcium is known to act as a key intracellular messenger in the perception of symbiotic signals by both the host plant and the microbial partner. Regulation of intracellular free Ca(2+) concentration, which is a fundamental prerequisite for any Ca(2+)-based signalling system, is accomplished by complex mechanisms including Ca(2+) binding proteins acting as Ca(2+) buffers. In this work we investigated the occurrence of Ca(2+) binding proteins in Mesorhizobium loti, the specific symbiotic partner of the model legume Lotus japonicus.

RESULTS

A soluble, low molecular weight protein was found to share several biochemical features with the eukaryotic Ca(2+)-binding proteins calsequestrin and calreticulin, such as Stains-all blue staining on SDS-PAGE, an acidic isoelectric point and a Ca(2+)-dependent shift of electrophoretic mobility. The protein was purified to homogeneity by an ammonium sulfate precipitation procedure followed by anion-exchange chromatography on DEAE-Cellulose and electroendosmotic preparative electrophoresis. The Ca(2+) binding ability of the M. loti protein was demonstrated by (45)Ca(2+)-overlay assays. ESI-Q-TOF MS/MS analyses of the peptides generated after digestion with either trypsin or endoproteinase AspN identified the rhizobial protein as ferredoxin II and confirmed the presence of Ca(2+) adducts.

CONCLUSIONS

The present data indicate that ferredoxin II is a major Ca(2+) binding protein in M. loti that may participate in Ca(2+) homeostasis and suggest an evolutionarily ancient origin for protein-based Ca(2+) regulatory systems.

Quantitative proteomics: assessing the spectrum of in-gel protein detection methods

Proteomics research relies heavily on visualization methods for detection of proteins separated by polyacrylamide gel electrophoresis. Commonly used staining approaches involve colorimetric dyes such as Coomassie Brilliant Blue, fluorescent dyes including Sypro Ruby, newly developed reactive fluorophores, as well as a plethora of others. The most desired characteristic in selecting one stain over another is sensitivity, but this is far from the only important parameter. This review evaluates protein detection methods in terms of their quantitative attributes, including limit of detection (i.e., sensitivity), linear dynamic range, inter-protein variability, capacity for spot detection after 2D gel electrophoresis, and compatibility with subsequent mass spectrometric analyses. Unfortunately, many of these quantitative criteria are not routinely or consistently addressed by most of the studies published to date. We would urge more rigorous routine characterization of stains and detection methodologies as a critical approach to systematically improving these critically important tools for quantitative proteomics. In addition, substantial improvements in detection technology, particularly over the last decade or so, emphasize the need to consider renewed characterization of existing stains; the quantitative stains we need, or at least the chemistries required for their future development, may well already exist.

Serum hyaluronidase aberrations in metabolic and morphogenetic disorders

Hyaluronidases are endo-glycosidases that degrade both hyaluronan (hyaluronic acid) (HA) and chondroitin sulfates. Deficiency of hyaluronidase activity has been predicted to result in a phenotype similar to that observed in mucopolysaccharidosis (MPS). In the present study, we surveyed a variety of patients with phenotypes similar to those observed in MPS, but without significant mucopolysacchariduria to determine if some are based on aberrations in serum hyaluronidase (Hyal-1) activity. The study included patients with well-characterized dysmorphic disorders occurring on genetic basis, as well as those of unkown etiology. The purpose of the study was to establish how wide spread were abnormalities in levels of circulating Hyal-1 activity. A simple and sensitive semi-quantitative zymographic procedure was used for the determination of activity. Levels of both beta-N-acetylglucosaminidase and beta-glucuronidase whose activities contribute to the total breakdown of hyaluronan (HA) were also measured, as well as the concentration of circulating HA. Among 48 patients with bone or connective tissue abnormalities, low levels of Hyal-1 activity were found in six patients compared to levels in 100 healthy donors (2.0-3.2 units/microL vs 6(+/- 1 SE) units/microL). These six patients exhibited a wide spectrum of clinical abnormalities, in particular shortened extremities: they included three patients with unknown causes of clinical symptoms, one patient with Sanfilippo disease, one of the seven patients with achondroplasia, and one with hypophosphotemic rickets. Normal levels of serum Hyal-1 activities were found in patients with Morquio disease, GM1 gangliosidosis, I cell-disease, 6 of the 7 patients with achondroplasia, Marfan's-syndrome and Ehlers-Danlos syndrome. No patient totally lacked serum Hyal-1 activity. Serum HA concentration was elevated in patients with Sanfilippo A and I-cell disease. Determination of serum and leukocyte Hyal-1 and serum HA may be useful to evaluate patients with metabolic and morphogenetic disorders.

Characterization of monoclonal antibodies directed to canine T lymphocyte markers expressed during development

Two monoclonal antibodies (mAb) which recognize cell surface antigens of canine T lymphocytes are described. mAb RQ1 (of IgG1 subclass) binds a 34 kDa peptide under non-reducing conditions which is expressed, on average, by 27 +/- 9% (n = 11 dogs) of thymocytes, with preferential binding for medullary, but not cortical thymocytes. RQ1 adheres to splenic periarteriolar lymphoid sheath cells. In adult dogs (n = 7) RQ1 binds on average 86 +/- 7% of unstimulated canine peripheral blood mononuclear cells (CPBMC), 69 +/- 13% (n = 11) of lymph node cells, and < or = 19% (n = 2) of bone marrow cells. RQ1 does not bind canine granulocytes, erythrocytes, fibroblasts or kidney epithelial cells. The relative density of RQ1-binding antigen (expressed as fluorescence intensity per cell) was up to 83% greater in lymph node cells than in thymocytes. Thus RQ1 appears to preferentially bind mature T cells. In contrast, mAb LQ1 (of IgG3 subclass, which binds a 32 kDa sialic acid containing glycoprotein) recognizes both cortical and medullary canine thymocytes as well as 75 +/- 6% CPBMC. This profile is characteristic of a pan-T cell marker. The simultaneous utilization of these two markers allows for the characterization of canine T lymphocyte development: early lymphocyte (e.g. LQ1+, RQ1- thymocytes), common lymphocyte (e.g. LQ1+, RQ1+ [dim fluorescence] thymocytes), and mature lymphocyte (e.g. LQ1+, RQ1 + [bright fluorescence]).

Developmental expression of a tandemly repeated, proline-and glutamine-rich amino acid motif on hyphal surfaces on Candida albicans

cDNA sequences encoding a cell wall protein have been isolated from the opportunistic pathogen, Candida albicans, an organism that can cause serious disease in immunocompromised patients such as those with AIDS. The cDNA encodes a peptide that is largely composed of an acidic, repeated motif 10 amino acids in length that is rich in proline and glutamine residues. The cDNA gene product was found to be present on hyphal surfaces by immunofluorescence assays using monospecific antisera raised to the recombinant protein produced in Pichia pastoris. The hyphae-specific surface location was also seen on organisms colonizing the gastrointestinal mucosa of mice, indicating that the antigen is produced and developmentally regulated during growth in host tissues. The cDNA clone hybridized to an abundant messenger RNA 2.3 kilobases in size that was present in hyphal but not yeast forms. These studies demonstrate that the bud-hypha transition is accompanied by the de novo synthesis of proteins that are targeted to hyphal surfaces. The primary sequence of the unique amino acid motif shares features with surface proteins of other lower eukaryotic microorganisms and with host acidic salivary proline-rich proteins.

Staining methods in gel electrophoresis, including the use of multiple detection methods

Polyacrylamide gel electrophoresis is a reliable and widely used technique for the separation, identification and characterization of proteins and protein mixtures. With the introduction of high resolution two-dimensional polyacrylamide gel electrophoresis in 1975 upward to 2000 individual polypeptides spots are easily separated on a single electrophoretic gel thereby necessitating the availability of highly sensitive protein detection methods. Although a plethora of protein-staining and -visualization protocols have been described utilizing both radioactive and non-radioactive reagents, many times the use of mono-dimensional detection procedures is insufficient to address the experimental questions asked. The present review highlights the utilization of combined protein-labeling and -staining methodologies in gel electrophoresis including selected applications in polyacrylamide gels and solid membrane matrixes.

A major surface antigen of procyclic stage Trypanosoma congolense

Five monoclonal antibodies (mAb) were raised that bound to the surface of procyclic stage Trypanosoma congolense with high intensity in immunofluorescence. Immunoblot analysis of trypanosome lysates using 3 of these mAb revealed a diffuse SDS-PAGE band of 36-40 kDa. The purified antigen did not react with Coomassie Blue or silver stains, but did stain blue with Stains-all, indicating acidity. For the one mAb tested, the epitope was periodate-sensitive and therefore probably glycan. Although this antigen shares properties with procyclin/PARP, which forms a surface coat on procyclic Trypanosoma brucei, a search in T. congolense for homologues of a procyclin/PARP gene revealed only non-coding sequence of partial similarity. Using a differential screen, a procyclic stage T. congolense cDNA clone was isolated that encoded a putative 256-amino acid protein containing 2 peptides chemically sequenced independently by Beecroft et al. [36]. The protein, termed glutamate and alanine-rich protein (GARP), has potential hydrophobic leader and tail sequences (the latter with potential for replacement by a glycosyl phosphoinositol anchor) and no potential N-linked glycosylation sites. It has no significant sequence homology with known proteins. Antibodies against a translational fusion of GARP bound specifically in Western blots to a band very similar to that detected by the mAb and also to the purified antigen. Immunogold electron microscopy revealed a dense packing of the antigen on the cell surface. It appears that procyclic T. brucei and T. congolense have major surface proteins with structural analogy, but with no sequence homology.

A high-molecular-weight (greater than 8.10(5)) non-collagenous glycoprotein is synthesized by bovine cartilage in vitro

A high-molecular-weight (greater than 8.10(5)) glycoprotein was detected in [3H]glucosamine-labeled bovine cartilage. Extraction with varying amounts of guanidinium chloride showed that the molecule was not tightly bound to other matrix substances. Enzyme digestions identified the molecule as a non-collagenous glycoprotein. This glycoprotein constituted 10-20% of the [3H]glucosamine-labeled macromolecular material that was released into culture medium on the first day after labeling. The 3H-labeled glycoprotein was purified by anion-exchange chromatography, CsCl gradient centrifugation and gel filtration. The purified glycoprotein appeared on an SDS-polyacrylamide gel as one slightly polydisperse band, which could not be reduced by beta-mercaptoethanol.

Proteins of muscle subcellular fractions in Duchenne progressive muscular dystrophy stained with "stains-all" cationic carbocyanine dye and with Coomassie Blue

The protein compositions of subcellular fractions of muscle obtained from 17 Duchenne dystrophy patients, 15 disease controls (10 different primary myopathies, 5 spinal muscular atrophy patients), and 10 normals were examined by polyacrylamide gel electrophoresis. The gels were stained with Coomassie Brilliant Blue and with "Stains-all," which stains calcium-binding proteins, sialic acid-rich glycoproteins, and phosphoproteins. In muscle membrane fractions of Duchenne dystrophy patients there was a marked reduction in the concentrations of calsequestrin and a 39 kDa protein that stained blue with "Stains-all." There were changes in the proteins of all subcellular fractions of Duchenne's patients; some of these changes appear to be specific for Duchenne dystrophy (DD). There was no apparent correlation between the protein changes observed on acrylamide gels and the age of the patients, the duration of the disease, the degree of disability, or activity of creatine kinase. A decreased level of calsequestrin in DD sarcoplasmic reticulum may contribute to an increased level of free calcium seen in muscle from these patients.

Spinach ferredoxin is a calcium-binding protein

Spinach-leaf ferredoxin was identified as a calcium-binding protein by (45)Ca autoradiography on nitrocellulose membranes and with the cationic carbocyanine dye 1-ethyl-2-[3-(1-ethylnaphtho[1,2-d]thiazolin-2-ylidene)-2-methylpropenyl] naphtho[1,2-d]thiazolium bromide ("stains-all"). Binding of (45)Ca was observed at pH 6.8 and pH 7.8 and in the presence of 5 mM and 20 mM MgCl2. At the higher MgCl2 concentration the Ca(2+)-binding capacity is reduced. Only micromolar concentrations of LaCl3, however, are required to achieve a similar effect. Both the oxidized and reduced forms of ferredoxin bind calcium.

Identification of a major sialoprotein in the glycocalyx of human visceral glomerular epithelial cells

Glomerular visceral epithelial cells are endowed with a sialic acid-rich surface coat (the "glomerular epithelial polyanion"), which in rat tissue contains the sialoprotein podocalyxin. We have identified a major membrane sialoprotein in human glomeruli that is similar to rat podocalyxin in its sialic acid-dependent binding of wheat germ agglutinin and in its localization on the surface of glomerular epithelial and endothelial cells, as shown by immunoelectron microscopy, using the monoclonal antibody PHM5. Differences in the sialoproteins of the two species are indicated by the discrepancy of their apparent molecular weights in sodium dodecyl sulfate gels, by the lack of cross reactivity of their specific antibodies, and by the lack of homology of their proteolytic peptide maps. It is therefore possible that the human glomerular sialoprotein and rat podocalyxin are evolutionarily distinct, but have similar functions.

Localization of sialic acid in kidney glomeruli: regionalization in the podocyte plasma membrane and loss in experimental nephrosis

Sialic acid residues were localized by electron microscopy in renal glomeruli of normal and puromycin-treated rats with a cytochemical technique that utilized the Limax flavus lectin. In Lowicryl K4M thin sections from normal rats, sialic acid residues were found along the plasma membrane of the various glomerular cell types and in the glomerular basement membrane as well as the mesangial matrix. In NaDodSO4/PAGE, sialic acid residues of normal glomeruli were mainly confined to a 140-kDa protein previously identified as podocalyxin. The distribution of sialic acid residues in the podocyte plasma membrane was found to be remarkably regionalized. Based on the differential labeling intensity, three plasma membrane domains could be defined: the foot process base, the foot process region above the slit diaphragm, and the body of podocytes. Cytochemical and biochemical analysis of glomeruli from puromycin-treated rats showed a loss of sialic acid residues from glomerular sialoglycoconjugates indicating a perturbated glycosylation.

An oviductal fluid glycoprotein associated with ovulated mouse ova and early embryos

This study documents a molecular change in the murine ovum related to its exposure to oviductal fluid. Wheat germ agglutinin (WGA) identifies a 215-kDa glycoprotein band (GP215) that is associated with ovulated oocytes and early embryos obtained from the oviduct, but is absent from preovulatory oocytes. GP215 is present in ovarian bursal fluid, oviductal fluid, oviductal epithelial cell extracts, and medium conditioned by oviductal tissue in vitro. Preovulatory oocytes acquire GP215 after in vitro incubation in ovarian bursal fluid. Thus, it appears likely that GP215 is secreted by the oviductal epithelium and becomes intimately associated with the ovum following ovulation.

Sialoglycoproteins with a high amount of O-glycosidically linked carbohydrate moieties stain yellow with silver in sodium dodecyl sulfate-polyacrylamide gels

Several sialoglycoproteins and human salivary proteins were analyzed in sodium dodecyl sulfate-polyacrylamide gels using the silver/Coomassie-staining protocol (J. K. Dzandu, M. E. Deh, D. L. Barratt, and G. E. Wise, 1984, Proc. Natl. Acad. Sci. USA 81, 1733-1737) to determine the extent to which yellow Ag staining originally reported for human red blood cell glycophorins can be applied to other sialoglycoproteins. Results showed that not all sialoglycoproteins elicit a positive yellow color in the silver stain reaction. Some of the sialoglycoproteins stained as brown or negative images in the Ag-staining cycle. Alkaline beta elimination of O-glycosidically linked carbohydrate chains of glycophorin resulted in the loss of yellow color development in the Ag-staining protocol. Analysis of acidic salivary proteins showed several yellow Ag-stained bands at Mr X 10(-3) = 150, 82, 70, 51, 46, and 42. These results suggest that the carbohydrate moieties of glycophorin removable by alkaline beta elimination are responsible for the characteristic yellow color in the Ag stain reaction. In addition, under our staining conditions sialoglycoproteins with a high amount of O-glycosidically linked carbohydrate chains give a characteristic yellow silver stain.

Mapping of three carbohydrate attachment sites in embryonic and adult forms of the neural cell adhesion molecule

The sialic-rich carbohydrate moiety of the neural cell adhesion molecule (N-CAM) undergoes major structural changes during development and plays a significant role in altering the homophilic binding of the molecule. In order to understand the mechanism of these changes, a cyanogen bromide (CNBr) fragment that contained 90% of the sialic acid of N-CAM was isolated and characterized according to the number of carbohydrate attachment sites and reactivity with specific monoclonal antibodies. The CNBr sialopeptide migrated on SDS PAGE as a broad zone of Mr 42,000-60,000. Upon treatment with neuraminidase, it was converted to a single component of Mr 42,000, and subsequent, limited treatment with endoglycosidase F gave four evenly spaced components of Mr 35,000-42,000, suggesting that it contained three attachment sites for N-linked oligosaccharides. The fragment reacted with monoclonal antibody 15G8, which detects the sialic acid in embryonic N-CAM, and with a monoclonal antibody, anti-(N-CAM) No. 2. Treatment with neuraminidase or with endoglycosidase F destroyed reactivity with 15G8 but not with anti-(N-CAM) No. 2. A similar CNBr sialopeptide was obtained from adult N-CAM; it contained sialic acid, had three N-linked oligosaccharides and reacted with anti-(N-CAM) No. 2 but not with 15G8 monoclonal antibodies. A peptide fragment, Fr2, comprising the NH2 terminal and middle regions of the molecule yielded a CNBr fragment closely similar to the fragment obtained from the whole molecule. The CNBr fragment from Fr2 reacted with monoclonal antibody anti-(N-CAM) No. 2. Fr1, comprising the NH2 terminal region alone, failed to react. These data confirm that the majority of the sialic acid is localized in the middle region of the N-CAM molecule and support the hypothesis that embryonic to adult conversion of N-CAM is the result of differences in sialidase or sialytransferase activity.

Identification and characterization of podocalyxin--the major sialoprotein of the renal glomerular epithelial cell

The glomerular epithelial polyanion is a specialized cell surface component found on renal glomerular epithelial cells (podocytes) that is rich in sialoprotein(s), as detected by staining with cationic dyes (colloidal iron, alcian blue) and wheat germ agglutinin (WGA). We have isolated rat glomeruli and analyzed their protein composition by SDS PAGE in 5-10% gradient gels. When the gels were stained with alcian blue or "Stains All," a single band with an apparent Mr of 140,000 was detected that also stained very prominently with silver, but not with Coomassie Blue. This band predominated in fluorograms of gels of isolated glomeruli that had been labeled in their sialic acid residues by periodate-[3H]borohydride. In lectin overlays, the 140-kilodalton (kd) band was virtually the only one that bound [125I]wheat germ agglutinin, and this binding could be prevented by predigestion with neuraminidase. [125I]Peanut lectin bound exclusively to the 140-kd band after neuraminidase treatment. An antibody was prepared that specifically recognizes only the 140-kd band by immunoprecipitation and immuneoverlay. By immunoperoxidase and immunogold techniques, it was localized to the surface coat of the glomerular epithelium and, less extensively, to that of endothelial cells. When analyzed (after electroelution from preparative SDS gels), the 140-kd band was found to contain approximately 20% hexose and approximately 4.5% sialic acid. These findings indicate that the 140-kd protein is the major sialoprotein of the glomerulus, and it is the only component of glomerular lysates with an affinity for cationic dyes and lectins identical to that defined histochemically for the epithelial polyanion in situ. Since this molecule is a major component of the cell coat or glycocalyx of the podocytes, we have called it "podocalyxin."

Chemical and immunochemical characterization of caseins and the major whey proteins of rabbit milk

Caseins were separated from whey proteins by acid precipitation of skimmed rabbit milk. Whole casein was resolved by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis into three major bands with apparent relative molecular masses (Mr of 31 000, 29 000 and 25 000. On agarose/urea-gel electrophoresis whole casein gave three bands with electrophoretic mobilities alpha, beta and gamma. The three components were purified by DEAE-cellulose chromatography under denaturing and reducing conditions. Each was shown to have a different amino acid, hexose and phosphorus content, as well as non-identical peptide fragments after proteinase digestion. The 31 000 Da (dalton) protein, of alpha-electrophoretic mobility, had a high phosphorus content (4.38%, w/w); the 29 000 Da peptide, of gamma-mobility, had the highest hexose content (2.2%, w/w), contained 0.8 cysteine residue per 100 amino acid residues and was susceptible to chymosin digestion corresponding thus to kappa-casein; the 25 000 Da protein migrated to the beta-position. The rabbit casein complex is composed of at least three caseins, two of which (alpha- and kappa-caseins) are analogous to the caseins from ruminants. Although caseins are poor immunogens, specific antibodies were raised against total and purified polypeptides. The antiserum directed against whole casein recognized each polypeptide, each casein corresponding to a distinct precipitation line. The antisera directed against each casein polypeptide reacted exclusively with the corresponding casein and no antiserum cross-reaction occurred between the three polypeptides. From whey, several proteins were isolated, characterized and used as antigens to raise specific antibodies. An iron-binding protein with an apparent Mr of 80 000 was shown to be immunologically and structurally identical with serum transferrin.

Isolation of anionic sialoproteins from the rat glomerulus

The epithelial glomerular polyanion (GPA) designates an array of sialic acid-containing sites along the surface of the glomerular epithelium which react with cationic dyes or probes. In this work, sequential rat glomerular isolation, ultrasonic disruption, trypsin digestion, ion-exchange chromatography, and preparative polyacrylamide gel electrophoresis have been used to isolate anionic sialoglycoproteins from the glomerular epithelium. Because colloidal iron (CI) reactivity has been used to define the GPA histologically, we used a modification of the CI reaction to monitor and direct the isolation procedure. Three major fractions have been recognized and isolated in homogeneity. Antibodies to two of the fractions have been raised by immunization in rabbits. Indirect immunofluorescent and peroxidase-antibody techniques have localized both antigens to the glomerular visceral epithelium of normal rat kidney. This identification and definition of components of the GPA is valuable in delineating a role for GPA in glomerular function.

Characterization of rat somatotroph and mammotroph secretory granules. Presence of sulfated molecules

The contents of a purified somatotroph and mammotroph secretory granule fraction isolated from rat anterior pituitaries were solubilized in 4 M urea and analyzed by PAGE. In gels electrophoresed under a variety of conditions and stained with Coomassie Blue only two major bands, identified as GH and PRL, were present. In gels stained with Stains-All (which stains anionic substances), several additional bands were detected. When quarter pituitaries were labeled with a [3H]amino acid mixture, GH and PRL accounted for greater than 95% of the radioactivity incorporated into the granules. After labeling with [35S]sulfate, two classes of radiolabeled sulfated components were detected in the granules: a class of trypsin-sensitive macromolecular components which were coincident with two of the bands seen after Stains-All, and a class of low molecular weight components. In order to examine the distribution of the two classes of sulfated components within somatotroph and mammotroph granules, granules were suspended in 0.4% (w/v) Lubrol PX at pH 4.0, a treatment which has been shown to selectively solubilize somatotroph granule contents leaving mammotroph granule cores intact. This treatment was found to solubilize greater than 95% of the GH and greater than 99% of the radiolabeled, low molecular weight sulfated components; in contrast, there was virtually no solubilization of either PRL or macromolecular sulfated components. The findings indicate (a) that [35S]sulfate is incorporated into both somatotroph and mammotroph granules, and (b) that the low molecular weight sulfated components are associated with somatotroph granules whereas the macromolecular sulfated components are associated with mammotroph granules.

Molecular weights of three mouse milk caseins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and kappa-like characteristics of a fourth casein

Caseins of mouse milk are phosphoproteins which precipitate at pH 4.6, stain blue with "Stains-all," and stain red with "Stains-all" following alkaline phosphatase digestion. Four caseins were separated electrophoretically in sodium dodecyl sulfate-polyacrylamide gels varying from 8.5 to 15% acrylamide. Molecular weights for three of these proteins were 43,200, 27,700, and 25,900. The molecular weights determined for bovine alphas1 and beta caseins by this method were similar to those previously obtained by other methods. A fourth mouse casein contained carbohydrate, phosphorus, and sialic acid. This protein was rennin-sensitive and behaved anomalously on sodium dodecyl sulfate polyacrylamide gels, as did bovine kappa-casein. Because of similarities with bovine kappa-casein, it was designated with "kappa-casein" of mouse milk.

Isolation and characterization of a hemagglutinin from Amphitrite ornata, a polychaetous annelid

Extracts of the marine polychaetous annelid, Amphitrite ornata, agglutinate rat, rabbit, chicken and human erythrocytes and in other work have been shown to inhibit the growth of Ehrlich ascites tumors in mice. Fractionation of extracts on Sephadex G-100 gave three active fractions with molecular weights of 30 000, 54 000 and 100 000. The 30 000 dalton fraction (B) was purified 72-fold by ammonium sulfate precipitation, gel filtration and preparative disc gel electrophoresis. The purified hemagglutinin, amphitritin, was homogenous on analytical disc gel electrophoresis at four different pH values and gave a sharp boundary in sedimentation velocity ultracentrifugation. The three fractions showed paralled specificity toward rat and chicken erythrocytes, the former giving the higher titer. The purified agglutinin was active toward human blood groups A, B and O and exhibited 4-fold higher activity toward group A. The hemagglutinin titer against rat red blood cells was lowered only by N-acetylgalactosamine, the terminal sugar residue of the group A determinant. None of the saccharides tested inhibited agglutination of chicken erythrocytes. Hemagglutinin activity was insensitive to dialysis or treatment with EDTA. The activity was not affected by digestion with trypsin or pronase, but was destroyed by phenol extraction. Analytical disc gel electrophoresis showed one protein band with high anodal mobility at pH 8.5, which was not affected by proteolytic enzymes but was removed by phenol. Activity was unaffected by heating at 70 degrees C for 30 min but was destroyed by similar treatemtn at 85 degrees C. Activity was at a maximum at pH 7-9 and decreased reversibly down to pH 4 at which point it was irreversibly inactivated. The higher molecular weight agglutinin (A1) could be dissociated to give amphitritin by treatment with 6M urea of precipitation in 55% (NH4)2SO4. This dissociation was not reversed by dialysis. Amphitritin is a glycoprotein with a molecular weight determined by gel filtration of 30 000 and by approach to equilibrium sedimentation of 32 000. Amino acid analysis showed a preponderance of aspartic and glutamic acids and relatively large amounts of glycine, proline, alanine, valine and cysteine. The carbohydrate moeity which represented 12.8% of the molecule, contained mannose, galactose, glucosamine and sialic acid. Amphitritin is the first hemagglutinin to be isolated from a polychaetous annelid.

Reconstitution of D-glucose transport catalyzed by a protein fraction from human erythrocytes in sonicated liposomes

A protein fraction was obtained from human erythrocyte ghosts by solubilization with Triton X-100 or octylglucoside. Triton X-100 was removed from the protein by Bio-Beads SM-2 and octylglucoside, by diafiltration. The solubilized protein fraction catalyzed D-glucose uptake when reconstituted in sonicated liposomes. The uptake was time dependent and inhibited by mercuric ions or cytochalasin B. The results indicate that the uptake represents transport of the sugar into the liposomes rather than binding to the reconstituted liposomes.

Characterization of major milk proteins from BALB/c and C3H mice

Milk proteins from BALB/c and C3H mice were characterized with respect to their electrophoretic migration in polyacrylamide gels under alkaline and acid conditions. The major casein and whey proteins from each strain migrated similarly under the conditions employed. Phosphoproteins were identified by staining with "Stains-all" and by changes in electrophoretic mobility and staining induced by prior treatment with phosphatase. Sialic acid-rich glycoproteins were identified by staining with periodic acid-Schiff and with "Stains-all" by prior treatment with neuraminidase to identify sialic acid as the acidic portion of the molecule. The two major whey proteins were characterized further by their migration in sodium dodecyl sulfate gels. One protein had the same mobility as mouse serum albumin. The other protein migrated with a mobility similar to that of bovine alpha-lactalbumin. The identity of the former protein was confirmed by its reaction with goat anti-mouse serum albumin in an immunodiffusion procedure, and the latter protein by its B protein activity in the lactose synthetase assay.