Induction of acrosomal exocytosis in chicken spermatozoa by inner perivitelline-derived N-linked glycans.

In birds, the ovum is surrounded by a glycoprotein coat known as the inner perivitelline layer (IPVL), which is analogous to the mammalian zona pellucida and, as such, is the site of initial sperm binding and induction of acrosomal exocytosis (the acrosome reaction). In this study, we demonstrate that oligosaccharides isolated from chicken-IPVL glycoproteins are capable of inducing the acrosome reaction in chicken spermatozoa. Preparations containing only O-linked glycans were unable to induce the acrosome reaction whereas N-linked oligosaccharides released from the IPVL by PNGaseF treatment could induce the acrosome reaction. Addition of galactose to terminal N-acetyglucosamine residues suppressed the acrosome reaction-inducing capacity of the oligosaccharide preparation; however, this capacity could be restored by co-incubation with beta-galactosidase. This evidence suggests that the acrosome reaction-inducing factor is probably an N-linked oligosaccharide with terminal N-acetyl-glucosamine residues.

Identification of perivitelline N-linked glycans as mediators of sperm-egg interaction in chickens.

This study demonstrates that carbohydrates play an essential role in sperm-egg interactions in birds. Sperm-egg interaction was measured in vitro as the ability of spermatozoa to hydrolyse a small hole in the inner perivitelline layer, the equivalent of the mammalian zona pellucida. Preincubation with Triticum vulgaris lectin (WGA) and succinyl-WGA (S-WGA) at 10 microgram ml(-1) resulted in complete inhibition of sperm-egg interaction, whereas at the same concentration a range of other lectins (Canavalia ensiformis (Con A), Arachis hypogea (PNA), Ulex europaeus II (UEA II), Solanum tuberosum (STA), Tetragonolobus purpureas (LTA) and Pisum sativum (PSA)) were unable to inhibit sperm egg interaction significantly, although fluorescein-labelled derivatives of these lectins were found to stain the inner perivitelline layer. Significant inhibition of sperm-egg interaction was achieved by the addition of N-acetyl-D-glucosamine and fucoidin to the assay mixture; however, D-glucose, D-galactose, D-fucose and L-fucose had no significant effect on sperm-egg interaction. Pretreatment of the inner perivitelline layer with N-glycanase significantly reduced sperm-egg interaction, whereas treatment with O-glycanase had no effect. These results demonstrate that N-linked glycans play an essential role in sperm-egg interaction in chickens.

Outer membrane protein shifts in biocide-resistant Pseudomonas aeruginosa PAO1.

Benzisothiazolone (BIT), N-methylisothiazolone (MIT) and 5-chloro-N-methylisothiazolone (CMIT) are highly effective biocidal agents and are used as preservatives in a variety of cosmetic preparations. The isothiazolones have proven efficacy against many fungal and bacterial species including Pseudomonas aeruginosa. However, some species are beginning to exhibit resistance towards this group of compounds after extended exposure. This experiment induced resistance in cultures of Ps. aeruginosa exposed to incrementally increasing sub-minimum inhibitory concentrations (MICs) of the isothiazolones in their pure chemical forms. The induced resistance was observed as a gradual increase in MIC with each new passage. The MICs for all three test isothiazolones and a thiol-interactive control compound (thiomersal) increased by approximately twofold during the course of the experiment. The onset of resistance was also observed by reference to the altered presence of an outer membrane protein, designated the T-OMP, in SDS-PAGE preparations. T-OMP was observed to disappear from the biocide-exposed preparations and reappear when the resistance-induced cultures were passaged in the absence of biocide. This reappearance of T-OMP was not accompanied by a complete reversal of induced resistance, but by a small decrease in MIC. The induction of resistance towards one biocide resulted in the development of cross-resistance towards other members of the group and the control, thiomersal. It has been suggested that the disappearance of T-OMP from these preparations is associated with the onset of resistance to the isothiazolones in their Kathon form (CMIT and MIT).

Site-directed chemical conversion of serine to cysteine in penicillin acylase from Escherichia coli ATCC 11105. Effect on conformation and catalytic activity.

Penicillin acylase (EC 3.5.1.11) was completely inactivated with equimolar phenylmethane [35S]sulphonyl fluoride (PhMe35SO2F); the stability of the sulphonyl group in the modified protein was determined by measurement of the radioactivity in ultrafiltrates. In 8 M urea, the rate of loss of the sulphonyl group was similar to that observed in PhMeSO2F-inactivated chymotrypsin [Gold, A.M. & Fahrney, D. (1964) Biochemistry 3, 783-791]. Incubation of the PhMeSO2F-inactivated acylase with 0.7 M potassium thioacetate yielded an acetylthiol enzyme which was subsequently converted to a thiol-enzyme during incubation with 10 mM 6-aminopenicillanic acid. 4-Pyridyl-ethylcysteine was released by acid hydrolysis after reaction of the thiol-protein with 4-vinylpyridine. The rates of reaction of thiol-penicillin acylase with iodoacetic acid and 2,2'-dipyridyl disulphide were consistent with the presence of an incompletely accessible cysteinyl sidechain. After carboxymethylating the thiol-enzyme with iodo[2-3H]acetic acid, the label was shown by SDS/PAGE and sequencing analysis to be associated exclusively with the beta-chain NH2-terminal residue, indicating conversion of Ser290 to S-carboxymethyl-cysteine. Near-ultraviolet CD spectra showed the conformation of thiol-penicillin acylase to be indistinguishable from that of the native protein but the catalytic activity was less than 0.02% of that of the normal enzyme. The possibility that Ser290 acts as a nucleophile in catalysis is discussed.