N-糖蛋白去糖基化酶（PNGase）的研究进展

N-糖蛋白去糖基化酶（PNGase）是一种广泛存在于真菌、植物、哺乳动物中的去糖基化酶，可以水解N-糖蛋白或 N-糖肽上天冬酰胺与寡糖链连接的化学键，并释放出完整的N-寡糖。PNGase在生物体内参与蛋白质降解、器官发育、个体生长等过程。人PNGase基因功能缺陷会导致先天性去糖基化障碍，小鼠PNGase缺陷会导致胚胎致死性，线虫PNGase缺陷使其寿命下降。本文对PNGase在不同物种的分布、蛋白质结构、酶学功能及生物学功能进行阐述，为PNGase的生理病理功能及致病机制的基础研究提供思路，为PNGase作为糖生物学工具酶或药物开发的创新应用研究奠定基础。     

Cancer chemotherapy and somatic cell mutation

The occurrence of a second neoplasm is one of the major obstacles in cancer chemotherapy. The elucidation of the genotoxic effects induced by anti-cancer drugs is considered to be helpful in identifying the degree of cancer risk. Numerous investigations on cancer patients after chemotherapy have demonstrated: (i) an increase in the in vivo somatic cell mutant frequency (Mf) at three genetic loci, including hypoxanthine–guanine phosphoribosyl-transferase (hprt), glycophorin A (GPA), and the T-cell receptor (TCR), and (ii) alterations in the mutational spectra of hprt mutants. However, the time required for and the degree of such changes are quite variable among patients even if they have received the same chemotherapy, suggesting the existence of underlying genetic factor(s). Accordingly, some cancer patients prior to chemotherapy as well as patients with cancer-prone syndrome have been found to show an elevated Mf. Based on the information obtained from somatic cell mutation assays, an individualized chemotherapy should be considered in order to minimize the risk of a second neoplasm.     

Alterations in catalytic activity and virus maturation produced by mutation of the conserved histidine residues of herpes simplex virus type 1 protease.

Mutant herpes simplex virus type 1 (HSV-1) viruses were constructed to characterize the roles of the conserved histidine residues (H61 and H148) of HSV-1 protease in the regulation of catalytic activity and virus maturation. Viruses containing mutations at H61 (H61V-V711, H61Y-V715, and H61A-V730) were unable to grow on Vero cells. These mutant viruses could process neither Pra to N0 nor ICP-35cd to ICP-35ef. Transmission electron microscopy studies of H61A-V730-infected Vero cells indicated that capsid maturation is arrested at a state characterized by the predominance of large symmetrical arrays of B capsids within the nucleus. Two mutations at H148 (in viruses H148A-V712 and H148E-V728) gave rise to mutant viruses that grew with a small-plaque phenotype; one of the viruses, H148E-V728, was particularly attenuated when grown at a low multiplicity of infection. The rate of processing of Pra to N0 in infected Vero cells increased in the order H148A-V712 < H148E-V728 < parental strain HSV-1-V731. The observation that H148A-V712 processes Pra to N0 and ICP-35cd to ICP-35ef, whereas H61A does not, establishes H61 as the catalytically essential conserved His assuming that HSV-1 protease, like other serine proteases, utilizes an active-site histidine residue in catalysis. Two of the mutations at H148 (viruses H148K-V729 and H148Y-V716) produced nonviable viruses. H148K-V729 processed neither Pra to N0 nor ICP-35cd to ICP-35ef, whereas H148Y-V716 processed Pra to N0 but did not process ICP-35cd to ICP-35ef. The range of phenotypes observed with the H148 mutant viruses suggests that residue 148 of the HSV-1 protease is a determinant of virus growth rate and viability because of its effects on the activity of the protease and/or the role of the protease domain in capsid assembly and DNA packaging.     

Profile of the alpha-bungarotoxin-binding regions on the extracellular part of the alpha-chain of Torpedo californica acetylcholine receptor.

The continuous alpha-neurotoxin-binding regions on the extracellular part (residues 1-210) of the alpha-chain of Torpedo californica acetylcholine receptor were localized by reaction of 125I-labelled alpha-bungarotoxin with synthetic overlapping peptides spanning this entire part of the chain. The specificity of the binding was confirmed by inhibition with unlabelled toxin and, for appropriate peptides, with unlabelled anti-(acetylcholine receptor) antibodies. Five toxin-binding regions were localized within residues 1-10, 32-41, 100-115, 122-150 and 182-198. The third, fourth and fifth (and to a lesser extent the first and second) toxin-binding regions overlapped with regions recognized by anti-(acetylcholine receptor) antibodies. The five toxin-binding regions may be distinct sites or, alternatively, different 'faces' in one (or more) sites.     

In vivo phosphorylation of isocitrate lyase inEscherichia coli andAcinetobacter calcoaceticus

Isocitrate lyase inEscherichia coli and inAcinetobacter calcoaceticus is phosphorylated when the cells are grown with acetate as the sole carbon source in low-phosphate mineral salts medium containing³²P inorganic phosphate. The level of³²P incorporation into the enzyme in both microorganisms appears to be constant throughout the entire growth cycle. Further, theresults of immunoblots and rocket immunoelectrophoresis suggest that the amount of isocitrate lyase protein, although at different levels in each microorganism, also remains constant throughout the growth cycle.     

Effect of caffeine on the rho--induction with ethidium bromide in Saccharomyces cerevisiae

Summary It is shown that caffeine antagonizes petiteinduction with ethidium bromide under non-growth conditions when administered during or after mutagenic treatment.Caffeine itself is shown to be a petite-inducing agent when cells are grown in liquid glucose-completemedium in the presence of the drug.A possible mode of action of caffeine in the ethidium bromide induced petite-mutagenesis is discussed.