Effects of site-specific mutation on structure and activity of influenza virus B/Lee/40 neuraminidase

A cDNA copy of the neuraminidase (NA) gene of a high-growing reassortant influenza virus which has the hemagglutinin of B/Hong Kong/8/73 and the NA of B/Lee/40 was cloned into plasmid pUC 9 and subcloned into a late-replacement SV40 vector so that the NA gene could be expressed in eukaryotic cells. The expressed protein was antigenically and enzymatically active. To study structure-function relationships in the B/Lee NA, particularly in comparison to the known structure of influenza A (N2) NA, specific mutations were introduced using synthetic oligonucleotides. Mutation of an apparently unpaired cysteine residue to serine at position 251 had no effect on protein transport or folding as judged by cell-surface reactivity with monoclonal antibodies, and the NA retained enzyme activity, confirming that this Cys is not essential for correct folding of the polypeptide. Mutation of Trp 364 to Leu abolished detectable enzyme activity, while mutation of Thr 368 to Val reduced enzyme activity to less than 25% of wild-type levels. Neither mutation affected antigenic properties. Therefore it is likely that both these side chains extend into the NA active site pocket. The results of these experiments are in accord with similarities in the structure of the B/Lee NA compared with that of influenza A (N2) NA. Although there is about 70% amino acid sequence difference between influenza A and B NAs, residues in the active site are highly conserved. Our in vitro mutagenesis experiments help to confirm the tentative alignment of sequences and have identified conserved amino acid side chains involved in enzyme activity.

The effect of sodium selenite on chondrocytes in monolayer culture

The effect of sodium selenite on DNA and sulfated proteoglycan synthesis by cultured rabbit articular and growth plate chondrocytes was studied as an in vitro model for Kashin-Beck disease. The selenium content of a defined medium (DMEM, fibroblast growth factor, insulin, and dexamethasone) was below the limit of detection by isotope dilution mass spectrometry. The chondrocytes were viable in the Se-free basal medium. Selenite over a range of 5 X 10(-9) M to 5 X 10(-7) M had no stimulatory effect on DNA or sulfated proteoglycan synthesis by either type of chondrocyte or skin fibroblasts. Proliferation of bovine endothelial cells was enhanced by 5 X 10(-7) M Se. At Se concentrations of greater than or equal to 10(-6) M, there was progressive inhibition of cell growth and radiosulfate incorporation of the connective tissue cells; bovine endothelial cells were more resistant. Twice equimolar concentrations of vitamins C and E exerted no protective effect against the cytotoxicity of higher concentrations of Se. Se supplementation also failed to stimulate growth of human infant chondrocytes. The model enabled simulation of conditions of hyposelenosis below those encountered in nature. The data provide no evidence that chondrocytes have idiosyncratic requirements for Se, and do not support the hypothesis that Se deficiency is a major etiologic factor in Kashin-Beck disease.

X-ray microanalysis of resting and stimulated rat pancreas

The elemental distribution in acinar cells of rat pancreas was investigated by X-ray microanalysis of thin, freeze-dried cryosections. In the resting cell, the highest calcium concentrations were found in the basal part of the cell (including the endoplasmic reticulum) and in the zymogen granules. Mitochondrial calcium concentrations were low. Zymogen granules were rich in sulphur, but low in phosphorus, sodium and potassium. Stimulation of the pancreas by perfusion in vivo with the cholinergic agonist carbachol caused a significant decrease of the calcium concentration in the basal part of the cell and an increase in the calcium concentration in the apical part of the cell. The mitochondrial calcium concentration was not significantly altered. In addition, increased sodium and decreased potassium concentrations, giving rise to a significant increase in Na/K ratio were observed in all cell compartments measured, except in the zymogen granules.

The reserpinized rat in the study of cystic fibrosis: x-ray microanalysis of submandibular gland and pancreas

The chronically reserpinized rat has been suggested as an animal model for cystic fibrosis. X-ray microanalysis of thick and thin cryosections was carried out to assess elemental redistribution in the submandibular glands and the pancreas of reserpinized rats at the cellular and subcellular level. In the submandibular gland of reserpinized rats, calcium and magnesium concentrations were significantly elevated. Mucus globules, secretory granules, and endoplasmic reticulum were the primary sites of the localization of excess calcium and magnesium. A significant potassium loss from the gland had occurred, particularly from the serous cells. Electron microscopy of conventionally prepared tissue showed marked swelling of the endoplasmic reticulum, especially in mucous cells. The elemental changes in the pancreatic acinar cells of reserpinized rats were reminiscent of elemental redistribution connected with cell death: increased levels of sodium, chlorine, and calcium and decreased levels of magnesium and potassium. Ultrastructural changes included swelling of the endoplasmic reticulum and obstruction of the acinar lumen. It is concluded tha elemental redistribution in chronically reserpinized rats presents interesting parallels with cystic fibrosis.

Cryoultramicrotomy as a preparative method for x-ray microanalysis in pathology

The role of ion shifts in cell injury has become one of the most intriguing fields of application of X-ray microanalysis in pathology. In principle, cryo(ultra)-microtomy is the best preparative method for X-ray microanalysis of diffusible substances. In this review, the following points are discussed: the choice of freezing method and coolant, the use of high molecular weight polymer cryoprotectants and their possible physiological effects the choice of the cryosectioning temperature, and techniques for handling and transfer of sections. Experiences with the sectioning of cryoprotected tissue are presented. Finally, other preparative techniques for microanalysis are compared to cryoultramicrotomy.

Immunofluorescence localizations of proteins in semithin 0.2--1 micron frozen sections of the ear. A report of improved techniques including gelatin encapsulation and cryoultramicrotomy

The present work describes a high resolution technique for locating proteins in frozen sections of the inner ear by immunofluorescence. Dissected organs are encapsulated in gelatin, and sections 0.1--1 micron thick are cut at --100 degrees C in a cryoultramicrotome. These are labelled with antibodies against two cytoskeletal proteins, actin and tubulin. Actin, which had previously only been described in the sensory cells, is found in the supporting cells as well. Tubulin is identified in the supporting cells and in outer spiral nerve fibres.