Reductive cleavage of Xaa-proline peptide bonds by mild alkaline borohydride treatment employed to release O-glycosidically linked carbohydrate units of glycoproteins

Heterologous production of a new lanthipeptide boletupeptin using a cryptic biosynthetic gene cluster of the myxobacterium Melittangium boletus

Myxobacteria have comparatively large genomes that contain many biosynthetic genes with the potential to produce secondary metabolites. Based on genome mining, we discovered a new biosynthetic gene cluster of class III lanthipeptide in the genome of the myxobacterium Melittangium boletus. The biosynthetic gene cluster contained a precursor peptide-coding gene bolA, and a class III lanthipeptide synthetase-coding gene bolKC. The expression vector containing bolA and bolKC was constructed using synthetic DNA with codon-optimized sequences based on the commercially available vector pET29b. Co-expression of the two genes in the host Escherichia coli BL21(DE3) yielded a new class III lanthipeptide named boletupeptin. The structure of boletupeptin was proposed to have one unit of labionin, as determined by mass spectrometry experiments after reductive cleavage. This is the first report of a class III lanthipeptide from a myxobacterial origin.

Deglycosylation effect of the mammalian sperm maturation antigen (SMA2) on serological reaction and acrosome reaction

Spermatozoal membrane proteins are considered to possess several immunological unique characteristics as the cell is formed behind the blood-testes barriers. Major goat sperm maturation antigen (SMA2) contains one hexosamine along with mannose, galactose and glucose. In the present study, effects of deglycosylation of SMA2 antigen on immuno-reactivity and the serological activity was investigated. SMA2 glycoantigen showed positive immunoreactivity after treatment with sodium borohydride (NaBH(4)) and moreover this generated a 44 kDa protein band which was negative for periodic acid Schiff reagent. Trifluoromethanesulfonic acid (TFMS) caused aggregation and restricted the free mobility of the treated antigen on SDS-PAGE and the protein band generated by TFMS treatment also showed positive immuno-reactivity. The results supported the views that the protein portion retains its immuno-reactivity even after oxidation of the vicinal hydroxyl group of saccharide component of SMA2 antigen. These data suggest that immunodominent epitopes exist on the core protein by which the SMA2 antigen retains its immuno-reactivity even after disruption of the saccharide portion. Additional experiments demonstrate that protein epitopes have a role in capacitation and the acrosome reaction (AR) in presence of antibody which is raised against this protein part of SMA2 using the negative staining of FITC-PSA (fluorescein isothiocyanate-labeled Pisum sativum agglutinin) probe. Altogether these findings indicate that the protein portion of SMA2 might fulfill the serological activity of the antigen as well as the protein epitope affects the acrosome reaction. In view of this property, we propose that the protein portion of SMA2 antigen might be considered as a potential antigenic target for an immune response.

Small-scale analysis of O-linked oligosaccharides from glycoproteins and mucins separated by gel electrophoresis

A technique with subpicomolar sensitivity was developed for analyzing O-linked oligosaccharides released from glycoproteins separated by gel electrophoresis. The protocol involves gel electrophoresis, electroblotting to poly-(vinylidene fluoride) membrane, reductive beta-elimination, and analysis of released oligosaccharides by liquid chromatography coupled to negative ion electrospray mass spectrometry. It was also found that N-linked oligosaccharides could be recovered under the same conditions, found both as free oligosaccharides and as distinct glycopeptides created from reductive cleavage of the protein backbone, giving some information on site-specific glycosylation. The method was used to demonstrate that the difference between human alpha-2HS-glycoprotein isoforms separated by 2D-gel electrophoresis was partially due to sialylation of both O-linked and N-linked oligosaccharides. It was also shown that both acidic and neutral oligosaccharides could be recovered and analyzed simultaneously from high molecular mass (200,000-5,000,000 Da) highly glycosylated mucin glycoproteins collected from small intestine and saliva and separated by sodium dodecyl sulfate-agarose/polyacrylamide composite gels. Mass spectrometric data not only gave information about the mass distribution of the heterogeneous mixtures of oligosaccharides from [M - xH](x-) ions but also gave information about the isomeric heterogeneity of the oligosaccharides from their resolution by porous graphitized carbon chromatography. Tandem mass spectrometry was explored as a technique for distinguishing between oligosaccharide isomers with different sequences and also between oligosaccharides with the same sequence but with different linkage configurations.

Mass spectrometric determination of the sites of O-glycan attachment with low picomolar sensitivity

A sensitive protocol for unambiguously and positively identifying O-glycosylation sites in glycopeptides is described, based on beta-elimination of the glycan chain(s) using NH4OH. On glycan elimination, NH3 is incorporated into the amino acid residue(s) to which the glycan(s) had been attached, to yield a modified amino acid residue having a distinct mass. Electrospray ionization collision-induced dissociation tandem mass spectrometry allows the released, modified peptide to be sequenced and the site(s) of the modified amino acid residue(s) to be identified. The protocol has been optimized using a series of structurally related O-glycopeptides, and standard conditions are recommended for handling unknowns. We demonstrate that site determination can be achieved using as little as 1 pmol of starting material.

The elimination of O-linked glycans from glycoproteins under non-reducing conditions

A simple procedure is described for the elimination of O-linked glycans from bovine submaxillary mucin under non-reducing conditions, using triethylamine in aqueous hydrazine. The glycans were isolated as the hydrazones, which were converted to the reducing glycans by exchange with acetone in neutral aqueous solution. The glycan alditols obtained after reduction corresponded to those obtained by the reductive beta-elimination of O-glycans.

Evidence for unique homologous peptide sequences around the glycosylated seryl and threonyl residues in polysialoglycoproteins isolated from the unfertilized eggs of the Pacific salmon Oncorhynchus keta

Structures of glycopeptides obtained by exhaustive Pronase digestion of high molecular weight (1.7 X 10(5)) salmon egg polysialoglycoprotein have been elucidated. Six principal glycopeptides isolated by gel chromatography and DEAE-Sephadex A-25 chromatography in the absence or presence of borate ion were analyzed for their carbohydrate and amino acid composition, as well as amino acid sequence, and found to be of two distinct types: glycotripeptides, Thr*-Ser*-Glu, and glycotetrapeptides, Thr*-Gly-Pro-Ser, where an asterisk indicates the amino acid residues to which either the Gal beta 1----3GalNAc or Fuc alpha 1----3GalNAc beta 1----3Gal beta 1----4Gal beta 1----3GalNAc chain is attached. Their final yield corresponds to 64% of the original desialylated glycoprotein. In view of the simple amino acid composition of salmon egg polysialoglycoprotein (molar ratio Asp2Thr2Ser3Glu1Pro1Gly1Ala3) and the result of alkaline beta-elimination indicating three carbohydrate units linked to two of two threonine and one of three serine residues, a unique primary structure comprising repetitive sequences of the above two types of glycopeptides, which are interspersed by short nonglycosylated peptides consisting of alanine and aspartic acid, has been proposed for the core protein. The molecular secondary ion mass spectra of underivatized glycopeptides were used to obtain their structural information. The anomeric configuration of the proximal sugar-peptide linkages was proven to be alpha by proton nuclear magnetic resonance spectroscopy. This is the first systematic reported study of O-glycosidically linked glycopeptides by these instrumental methods.

O-linked oligosaccharides of mouse egg ZP3 account for its sperm receptor activity

Previously, we reported that ZP3, one of three different glycoproteins present in the mouse egg's zona pellucida, serves as a sperm receptor. Furthermore, small glycopeptides derived from egg ZP3 retain full sperm receptor activity, suggesting a role for carbohydrate, rather than polypeptide chain in receptor function. Here, we report that removal of O-linked oligosaccharides from ZP3 destroys its sperm receptor activity, whereas removal of N-linked oligosaccharides has no effect. A specific size class of O-linked oligosaccharides, recovered following mild alkaline hydrolysis and reduction of ZP3, is shown to possess sperm receptor activity and to bind to sperm. The results presented strongly suggest that mouse sperm bind to eggs via O-linked oligosaccharides present on ZP3.