[6] Analysis of sugars by automated liquid chromatography

Improvement of gel properties of dried egg white by modification with galactomannan through the Maillard reaction

The effects of Maillard reaction on gel properties of dried egg white (DEW) with galactomannan (GM) were investigated. Maillard-reacted DEW (MDEW) was prepared by dry-heating a mixture with a weight ratio of 1:4 of GM to DEW at 60 degrees C and 65% relative humidity. The modification of amino groups and polymerization of DEW proteins dry-heated with GM proceeded with increasing the dry-heating time. The covalent attachment of GM to DEW was confirmed from SDS-PAGE analysis. Gel strength and water-holding capacity of MDEW gels were higher than those of DEW dry-heated without GM (control DEW) and reached maximum after 3 days of dry-heating. The appearance of MDEW gels became transparent with increasing the dry-heating time, but control DEW gels were still turbid. MDEW dry-heated for 3 days was almost soluble even after heating of its solution at 90 degrees C, whereas control DEW proteins precipitated. The modification of DEW with GM through the Maillard reaction was an effective method to make a firm and transparent gel from DEW at broader range of pH and NaCl concentration of the medium.

Structural elucidation of O-linked glycopeptides by high energy collision-induced dissociation

O-linked glycopeptides that bear a GalNAc core with and without the presence of sialic acid have been analyzed by high energy collision-induced dissociation (CID). We show that the CID spectra from the glycosylated precursor ions contain sufficient information to identify the peptide sequence and to determine the glycosylated site(s). Asialo O-linked glycopeptides, previously prepared from a tryptic digest of bovine fetuin were studied. One of the glycopeptides contained only a single Hex (hexose)-HexNAc (N-acetylhexosamine) substitution at Thr(262), whereas the other exhibited Hex-HexNAc moieties at both Thr(262) and Ser(264). In addition, sialo and asialo fetuin glycopeptides from a pronase digest were derivatized with t-butoxycarbonyl-tyrosine, and characterized by high energy CID analysis. The presence of a Galβ(1,3)GalNAc core structure at Ser(264) was confirmed by using the substrate specificity of endo-α-N-acetylgalactosaminidase. These studies revealed the presence of a β-galactosidase specific for β(1,4) linkages in the endo-α-N-acetylgalactosaminidase preparation employed. Finally, the relative stability of N-and O-glycosyl bonds to high energy CID is addressed based upon comparison of the behavior of a synthetic N-linked glycopeptide with analogous O-linked structures.

Antibodies directed against the thiomannose moiety of a glycoconjugate of 2-imino-2-methoxyethyl 1-thio-alpha-D-mannopyranoside and bovine serum albumin

Anti-thiomannose antibodies were induced in rabbits immunized with a glycoconjugate of 2-imino-2-methoxyethyl 1-thio-alpha-D-mannopyranoside (Man-S) and bovine serum albumin (BSA). Also anti-BSA antibodies directed against the BSA moiety of the glycoconjugate were detected in low concentrations in the immune serum. However, antibodies against the combinatorial epitope of the hapten group and the carrier protein were not detected. The anti-thiomannose and the anti-BSA antibodies were isolated in pure forms by affinity chromatography on Sepharose 4B-bearing thiomannosyl-BSA ligands or BSA ligands. The anti-thiomannose antibodies constituted the major fraction of the antibodies, and these antibodies were isolated in pure form for the first time. The specificity of the thiomannose antibodies was established from data of experiments of periodate oxidation, perpropionic acid oxidation, hapten inhibition, and agar diffusion, Isoelectrofocusing showed that the anti-thiomannose antibody preparation consisted of at least six isomeric proteins, all of which exhibited antibody activity against the glycoconjugate of thiomannose and BSA.

Preparation of a high-affinity photolabeling reagent for the Gal/GalNAc lectin of mammalian liver: demonstration of galactose-combining sites on each subunit of rabbit hepatic lectin

On the basis of the knowledge that the D-galactose/N-acetyl-D-galactosamine-specific lectin of rabbit liver can tolerate a large group on the C-6 hydroxyl group of a galactoside [Lee, R. T. (1982) Biochemistry 21, 1045-1050], we prepared a high-affinity photolabeling reagent for this lectin from a triantennary glycopeptide fraction of asialofetuin. The C-6 hydroxyl group of a D-galactopyranoside was converted, under mild conditions, into a primary amino group. The procedure involves conversion of the hydroxyl group to an oxo group with galactose oxidase, followed by reductive amination using benzylamine and sodium cyanoborohydride. Catalytic hydrogenolysis of the benzylamino derivative yielded the desired 6-amino-6-deoxy-D-galactoside. A 4-azidobenzoyl group was attached to the newly produced amino group to yield a photoactivatable affinity-labeling reagent. The reagent labeled the Triton-solubilized, purified hepatic lectins of rabbit and rat in a photo- and affinity-dependent manner. All the polypeptide subunits of the lectins were labeled, indicating that each subunit contains at least one D-galactose-combining site. In the case of the rabbit hepatic lectin, the minor subunit (46 kDa) was labeled more efficiently than the major one (40 kDa).

Different modes of ligand binding to the hepatic galactose/N-acetylgalactosamine lectin on the surface of rabbit hepatocytes

A study of the binding of three different 125I-labeled, galactose-terminated ligands to the hepatic galactose/N-acetylgalactosamine-specific lectin found on the surface of rabbit hepatocytes revealed that the different ligands manifest different physical parameters of binding. Asialoorosomucoid (125I-ASOR) binding was best described as involving two independent classes of binding sites on rabbit hepatocytes, with 161 000 sites/cell with a dissociation constant of 0.44 nM and 292 000 sites/cell with a Kd of 9.7 nM. Asialotriantennary glycopeptide purified from human alpha-1 protease inhibitor and modified with tyrosine at the N-terminus to permit radioiodination (TRI) [Lee, Y. C., Townsend, R. R., Hardy, M. R., Lönngren, J., Arnarp, J., Haraldsson, M., & Lönn, H. (1983) J. Biol. Chem. 258, 199-202] was also found to bind to two apparent classes of binding sites but with different binding parameters: 292 000 sites/cell of Kd = 1.47 nM and 982 000 sites/cell of Kd = 25.3 nM. A synthetic ligand, alpha,beta-diaspartamide of tris[(beta-lactosyloxy)methyl](6-aminohexanamido)methane (di-tris-lac) containing six nonreducing galactose residues [Lee, R. T., Lin, P., & Lee, Y. C. (1984) Biochemistry 23, 4255-4261], was found to bind to 817 000 sites/cell of Kd = 0.63 nM and 1.23 X 10(6) sites/cell of Kd = 25.3 nM. Thus, there were many more total binding sites for TRI or di-tris-lac on the surface of rabbit hepatocytes than there were for asialoorosomucoid, although the dissociation constants were similar for all three ligands.(ABSTRACT TRUNCATED AT 250 WORDS)

Purification and characterization of a 50,000 mol. wt glycoprotein antigen, and localization of determinants involved in cross-reactivity with carcinoembryonic antigen

A 50,000 mol. wt glycoprotein antigen (50 k) was purified from metastatic colon tumor. The initial purification was monitored by cross-reactivity of the antigen with an unabsorbed antiserum against carcinoembryonic antigen (CEA, Mr 180,000). Six mg of antigen was obtained from 250 g of tissue, with a recovery of 14% and a relative purification of 143-fold. The amino acid composition of 50 k was similar to that of CEA. The carbohydrate content, primarily glucosamine and mannose, totaled about 25%. Immunodiffusion showed that 50 k lacked some of the CEA epitopes, and that normal spleen contained an antigen identical to 50 k. Radioimmunoassays showed that the high avidity anti-CEA antibodies in the unabsorbed antiserum were mainly cross-reactive with 50 k, probably via a similar but not identical antigenic site. The immunochemical properties of 50 k thus correspond to those of the non-specific cross-reacting antigen (NCA). The molecular size and carbohydrate composition reported for various NCA-like antigens have differed, so identity of 50 k an NCA cannot be established on this basis. Immunoreactive fragments of 50 k were prepared by digestion with each of three different proteolytic enzymes, and were purified by high performance liquid chromatography (HPLC). A polypeptide of 20,000-30,000 mol. wt containing about half of the 50 k determinants, was recovered in each case. Experiments with mixtures showed that the three purified fragments all contained the same subset of antigenic determinants. The fragment-localized subset represented most, if not all of the 50 k determinants involved in CEA cross-reactivity. Similarly, a CEA fragment was shown to contain essentially all of the CEA determinants involved in 50 k cross-reactivity. The fragments of 50 k and CEA were quite resistant to further proteolytic digestion, and comparison of a CEA fragment with a 50 k fragment by partial acid hydrolysis and HPLC peptide mapping failed to reveal structural homology to account for the cross-reactivity.

An automated Elson-Morgan assay for 2-amino-2-deoxy-hexoses, with increased sensitivity

The Elson-Morgan assay for 2-amino-2-deoxyhexoses, despite its many modifications, can still give variable results because of slight variations in reaction conditions. An automated method is reported which uses microgram samples and provides greater sensitivity than hitherto possible. The use of sodium orthophosphate and optimisation of the concentrations of the reagents provide conditions that are more stable, and results that are more reliable, than any previously reported.

Purification and properties of human low molecular weight kininogen

A three-step isolation procedure has been developed for human low molecular weight kininogen resulting in a 385-fold purification of the protein from plasma with an accumulative yield of 8.4%. Human low molecular weight kininogen is a single-chain glycoprotein of apparent molecular weight of 68,000 with a blocked amino-terminus. In the absence of dissociating agents, low molecular weight kininogen reversibly forms homo-oligomers with apparent Mr 185,000 (dimer) to 780,000 (decamer). Limited proteolysis of low molecular weight kininogen by tissue kallikrein liberates kinin and results in the formation of a two-chain molecular with an Mr 62,000 heavy chain of apparent Mr 4000.

Lens plasma membrane: isolation and biochemical characterization

Lens plasma membrane from different animal lenses has been prepared by the acylation procedure. Using three different criteria: heat aggregation of intrinsic membrane polypeptides, immunochemistry and solubilization of intrinsic proteins at low (40 mM) LIS concentration, it has been shown that these preparations are essentially free of cytoplasmic contaminants. Using the results obtained with acylated membrane as the reference of purity, it has been shown that both sucrose gradient centrifugation of bovine WI protein and urea washing of old human lenses give impure membrane preparations. The main intrinsic polypeptides (mol. wt 26 000 and 22 000) of human lens membrane have been purified and characterized. It has been shown by enzymatic digestion and amino terminal analysis of the residual membrane-bound fragments that the amino terminal halves of the polypeptides are embedded in the lipid bilayer and are probably blocked at their amino terminal sites. Lipid analyses of human and bovine lens membranes suggest that the protein to total lipid ratio is 1:1. Carbohydrate analyses of chromatographically separated intrinsic membrane polypeptides indicate the presence of 1 mol glucose/1 mol protein.

Preparation of some (1 goes to 6)-linked disaccharides, and their derivatives suitable for protein modification

Synthetic methods for the preparation of per-O-acetylated, (1 goes to 6)-linked disaccharides containing either a D-galactose or a D-glucose residue at the reducing end are described. In these methods, 1,2,3,4-tetra-O-acetyl-6-O-trityl-beta-D-glucopyranose was first converted into 1,2,3,4-tetra-O-acetyl-beta-D-glucopyranose (1) by rapid treatment with 90% trifluoroacetic acid, followed by rapid isolation designed to minimize O-acyl migration. Disaccharides acid, followed by rapid isolation designed to minimize )-acyl migration. Disaccharides were formed by glycosylation of 1 or 1,2:3,4-di-O-isopropylidene-D-galactopyranose with per-O-acetylglycosyl halides. Isopropylidene groups in the resulting disaccharide, if present were removed, and the disaccharide was per-O-acetylated. Per-O-acetylated beta-Gal-(1 goes to 6)-Glc and beta-GlcNAc-(1 goes to 6)-Gal, and a mixture of per-O-acetylated alpha-Gal-(1 goes to 6)-Gal and beta-Gal-(1 goes to 6)-Gal (in the ratio of 3:7) were thus obtained. The per-O-acetylated Gal-(1 goes to 6)-Gal disaccharides were converted, by a reaction sequence previously reported, into (2,2-dimethoxyethyl)aminocarbonylmethyl 1-thio-beta-D-glycosides, which could then be coupled to proteins via reductive alkylation. For the anomeric mixture of per-O-acetylated Gal-(1 goes to 6(-Gal, conversion into the corresponding 1-thioglycoside permitted resolution of the isomers by chromatography on silica gel. When disaccharides, as borate complexes, were chromatographed on a column of a strong, anion-exchange resin, all of the (1 goes to 6)-linked disaccharides of neutral sugars tested (including melibiose) were eluted later than analogous disaccharides having other linkages, and also later than any neutral monosaccharides.

Isolation, characterization and localization of a 45 000 molecular weight, soluble glycoprotein from the lung in pulmonary alveolar proteinosis

A carbohydrate-rich, water-soluble glycoprotein has been isolated in pure form from delipidated lung lavage fluid from a patient with pulmonary alveolar proteinosis, in a three-step procedure involving ion-exchange and gel filtration chromatography. The molecular weight of the glycoprotein was determined to be 45 900 by sedimentation equilibrium analysis in the analytical ultracentrifuge and 45 000 by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, indicating a single polypeptide chain. Nearly half of the mass of the glycoprotein is comprised of carbohydrate that is contributed by 24 residues sialic acid, 23 residues N-acetylglucosamine, 6 residues N-acetylgalactosamine, 19 residues galactose, 4 residues mannose, 1 residue fucose and 1 residue glucose per mol. Unlike a number of collagen-related glycoproteins that have been isolated by others from insoluble lung contents in pulmonary proteinosis, the water-soluble glycoprotein described in the present report does not contain hydroxyproline or hydroxylysine and contains less than 10% of its amino acid residues as glycine. Using rabbit antibodies directed against our purest preparation of material and an immunoperoxidase staining procedure, the 45 000 molecular weight glycoprotein was localized to the thin film of fluid lining the surfaces of alveoli in normal human lungs.

Localization and overall structure of a mannose-rich glycopeptide from a pathologic immunoglobulin

The structure of a mannose-rich glycopeptide from a human pathological IgM has been investigated. It belongs to the group I (simple) glycopeptides and contains only mannose and N-acetylglucosamine residues in a molar ratio of 10:2. The structures of its oligosaccharide moiety and peptide chain have been determined: its molecular localization is specified and the relation between its biosynthesis and the oligosaccharide structure determine is discussed. Based on the alpha- and beta-mannosidase digestions and permethylation studies for the oligosaccharide moiety, and on the results obtained after sequential analysis of the peptide chain, the following structure is proposed for the mannose-rich IgM Du glycopeptide: (Formula: see text). The recovery of one molecule of this glycopeptide per molecule of heavy chain and the determination of the amino acid sequence have led us to locate this glycopeptide on asparagine 402 of the Fc portion of the heavy chain mu of IgM Du.

Attachment of thioglycosides to proteins: enhancement of liver membrane binding

Thioglycosides of D-galactose, D-glucose, N-acetyl-D-glucosamine, and D-mannose were covalently attached to Aspergillus oryzae alpha-amylase, hen's eggs lysozyme, and bovine serum albumin by amidination, diazo coupling, and amide formation. The binding of the newly formed glycoproteins (neoglycoproteins) to rabbit liver membranes was measured, using asialoorosomucoid as a reference. Attachment of D-galactosides by any of the three methods enhanced binding by several orders of magnitude. Coupling of a comparable number of D-mannosides or N-acetyl-D-glucosaminides had little or no effect. Attachment of D-glucosides also enhanced binding but to a variable extent depending on the method of attachment. Thus, the behavior of neoglycoproteins toward rabbit liver membranes closely paralleled that of serum glycoproteins (Ashwell and Morell, 1974) with respect to sugar specificity.

2-Imino-2-methoxyethyl 1-thioglycosides: new reagents for attaching sugars to proteins

Cyanomethyl 1-thioglycosides ofD-galactose, D-glucose, 2-acetamido-2-deoxy-D-glucose, and D-mannose were prepared from the respective pseudothiourea derivatives and chloroacetonitrile. The nitrile group in these cyanomethyl thioglycosides can be converted to a methyl imidate group by treatment with sodium methoxide or HC1 in dry methanol to yield 2-imino-2-methoxyethyl 1-thioglycosides (IME-thioglycosides). The factors influencing the yield of IME-thioglycosides were investigated. The most convenient method of preparing IME-thioglycosides was treating 0.1 M cyanomethyl thioglycoside peracetate in dry methanol with 0.01 M sodium methoxide at room temperature for 24-48 h (50-60% yield). These IME-thioglycosides reacted readily with simple amines, amino acids, and proteins in mildly alkaline buffer solutions. Alpha-amylase and lysozyme modified with these reagents under appropriate conditions retained full activities. Thus the IME-thioglycosides constitute a new group of reagents for attaching sugars to proteins.

Polyacrylamide gels copolymerized with active esters. A new medium for affinity systems

A new and versatile method for linking biologically active ligands to a polyacrylamide matrix is reported. Active esters of acrylic acid (N-succinimicyl acrylate and N-phthalimidyl acrylate) were synthesized, then copolymerized with acrylamide and N,N'-methylenebisacrylamide. Displacement of the active ester in the gel thus formed by various ligands containing aliphatic amino groups resulted in the formation of stable amid bonds between the ligands and the polyacrylamide gel. The affinity gel thus prepared has the following advantages: (i) resistance to chemical and microbiological degradation, (ii) ease of control of ligand level and higher levels of ligand possible, (iii) ease of control of porosity, and (iv) total displacement of the active ester under suitable conditions. Efficacy of this system was tested by preparation of 6-aminohexyl 2-acetamido-2-deoxy-beta-D-glucopyranoside derivative polyacrylamide gel by the described method. It was found to be more effective for purification of wheat germ agglutinin than the previously published affinity chromatography systems and the wheat germ hemagglutinin was obtained in crystalline form. In addition, partial resolution of isolectins was obtained from the affinity gel witha pH gradient.