Identification of Glycoproteins on Nitrocellulose Membranes Using Lectin Blotting

Botrytis cinerea protein O-mannosyltransferases play critical roles in morphogenesis, growth, and virulence

Protein O-glycosylation is crucial in determining the structure and function of numerous secreted and membrane-bound proteins. In fungi, this process begins with the addition of a mannose residue by protein O-mannosyltransferases (PMTs) in the lumen side of the ER membrane. We have generated mutants of the three Botrytis cinerea pmt genes to study their role in the virulence of this wide-range plant pathogen. B. cinerea PMTs, especially PMT2, are critical for the stability of the cell wall and are necessary for sporulation and for the generation of the extracellular matrix. PMTs are also individually required for full virulence in a variety of hosts, with a special role in the penetration of intact plant leaves. The most significant case is that of grapevine leaves, whose penetration requires the three functional PMTs. Furthermore, PMT2 also contributes significantly to fungal adherence on grapevine and tobacco leaves. Analysis of extracellular and membrane proteins showed significant changes in the pattern of protein secretion and glycosylation by the pmt mutants, and allowed the identification of new protein substrates putatively glycosylated by specific PMTs. Since plants do no possess these enzymes, PMTs constitute a promising target in the development of novel control strategies against B. cinerea.

Expression of recombinant human interferon-γ with antiviral activity in the bi-cistronic baculovirus-insect/larval system

A bi-cistronic baculovirus-insect/larval system containing a polyhedron promoter, an internal ribosome entry site (IRES), and an egfp gene was developed as a cost-effective platform for the production of recombinant human interferon gamma (rhIFN-γ). There was no significant difference between the amounts of rhIFN-γ produced in the baculovirus-infected Spodoptera frugiferda 21 cells grown in serum-free medium and the serum-supplemented medium, while the Trichoplusia ni (T. ni) and Spodoptera exigua (S. exigua) larvae afforded rhIFN-γ amounting to 1.08±0.04 and 9.74±0.35 µg/mg protein respectively. The presence of non-glycosylated and glycosylated rhIFN-γ was confirmed by immunoblot and lectin blot. The immunological activity of purified rhIFN-γ, with 96% purity by Nickel (II)-nitrilotriacetic acid (Ni-NTA) affinity chromatography, was similar to that commercially available. Moreover, the rhIFN-γ protein from T. ni had more potent antiviral activity. These findings suggest that this IRES-based expression system is a simple and inexpensive alternative for large-scale protein production in anti-viral research.

Characterisation of the carbohydrate fraction of the temporary adhesive secreted by the tube feet of the sea star Asterias rubens

In sea stars, adhesion takes place at the level of a multitude of small appendages, the tube feet. It involves the secretion of an adhesive material which, after tube foot detachment, remains on the substratum as a footprint. It was previously reported that the two main organic components of this material are proteins and carbohydrates. The carbohydrate moiety of the adhesive secretion of Asterias rubens was investigated using a set of 16 lectins which were used on sections through tube feet, on footprints, and on the proteins extracted from these footprints. After gel electrophoresis, these proteins separate into eight protein bands which were named sea star footprint proteins (Sfps). Eleven lectins label the tube foot epidermis at the level of the adhesive cells, four react with footprints, and eight with two of the extracted footprint proteins, which are therefore classified as glycoproteins. Sfp-290 appears to bear mostly N-linked oligosaccharides and Sfp-210 principally O-linked oligosaccharides. The outer chains of both glycoproteins enclose galactose, N-acetylgalactosamine, fucose, and sialic acid residues. Another part of the carbohydrate fraction of the footprints would be in the form of larger molecules, such as sialylated proteoglycans. These two types of glycoconjugates are presumably key components of the sea star temporary adhesive providing both cohesive and adhesive contributions through electrostatic interactions by the polar and hydrogen-bonding functional groups of their glycan chains.

Mucin degradation mechanisms by distinct Pseudomonas aeruginosa isolates in vitro

Pseudomonas aeruginosa has emerged as an important causative agent of bacterial keratitis, a rapidly progressive ocular condition that may result in blindness. Secretory mucin forms the main constituent of the precorneal tear film, a three-layer film on the ocular surface protecting the underlying corneal epithelium from potential pathogens. The purpose of the present study was to compare mucin degradation mechanisms between ocular P. aeruginosa strains. Mucin degradation was assessed by agarose electrophoresis, lectin blotting, and size exclusion chromatography. The results indicate that certain P. aeruginosa strains (Paer12, ATCC 15442, 6294, and Paer25) had depleted mucin from the culture supernatant and that this was contingent on the inherent ability of these isolates to produce proteases. Non-protease-producing strains (Paer1 and Paer3) did not appreciably degrade mucin. Further, galactosidase, N-acetylglucosaminidase, and N-acetylgalactosaminidase activities were detected in some strains, suggesting the operation of further mechanisms of mucin degradation by P. aeruginosa. Mucin degradation by P. aeruginosa also seemed to be for the acquisition of nutrients, as a growth advantage was observed in mucin-depleting strains over nondepleting strains in the long term. It is postulated that the degradation of mucin serves to collapse the mucin barrier and its associated network containing antibacterial tear components and to provide energy for sustained bacterial growth.