Aurin tricarboxylic acid, the anti-AIDS compound, prevents the binding of interferon-alpha to its receptor

Binding of HIV to its receptor, the CD4 molecule of lymphocytes, can be prevented by chemical agents. These agents could be considered as potential anti-AIDS drugs. We have shown that aurin tricarboxylic acid (ATA, 3 microM) specifically blocks the binding of gp120, the HIV coat protein, to the CD4 molecule. We have also found that ATA prevents the binding of interferon-alpha to its receptor in a dose-dependent manner (12-50 microM range). Membrane potential shift, associated with binding of interferon-alpha to its receptor, was also blocked by ATA in a dose-dependent fashion. Our results indicate that potential anti-AIDS drugs should be screened for such undesired side effects.     

Site-directed mutagenesis of La protease. A catalytically active serine residue.

Comparative sequence analysis of Escherichia coli ATP-dependent La protease led to the suggestion that Ser679 is the catalytically active enzyme residue. Site-directed mutagenesis Ser679----Ala, investigation of the cells containing the mutant plasmid, and study of the partially purified mutant protein produced results in favour of this suggestion.     

Post-translational processing of chicken bone phosphoproteins. Identification of the bone phosphoproteins of embryonic tibia.

After periodate oxidation and incubation with a dihydrazide, cross-linking of the two heavy chains of immunoglobulins G from several species proceeds specifically through their oligosaccharides. We have used malonic acid dihydrazide, adipic acid dihydrazide and dithiodipropionic acid dihydrazide. The last compound is introduced in this work as a cleavable-carbohydrate-specific cross-linker. It was found that in rabbit and human immunoglobulins the degree of cross-linking was strongly dependent on the oxidation conditions but only very weakly dependent on the concentration and size of the dihydrazides. Papain cleavage of the cross-linked rabbit IgG indicated that the cross-linking occurred predominantly, if not exclusively, in the Fc region, probably through the two glycans linked to Asn-297 in the CH2 domain of each of the two heavy chains. The immunoglobulins from sheep, pig, goat and guinea pig show a comparable cross-linking pattern, indicating that the sugar chains from these immunoglobulins have a spatial structure closely related to that of rabbit and human IgG. When dithiodipropionic acid dihydrazide was used as the cross-linker, the cross-link could be cleaved by mercaptoethanol.     

Isolation and characterization of a type II restriction endonuclease from Streptococcus thermophilus

The alpha-toxin (phospholipase C) of Clostridium perfringens has been reported to contain catalytically essential zinc ions. We report here that histidine residues are essential for the co-ordination of these ion(s). Incubation of alpha toxin with diethylpyrocarbonate, a histidine modifying reagent, did not result in the loss of phospholipase C activity unless the protein was first incubated with EDTA, suggesting that zinc ions normally protect the susceptible histidine residues. When the amino acid sequences of three phospholipase C's were aligned, essential zinc binding histidine residues in the non-toxic B. cereus phospholipase C were found in similar positions in the toxic C. perfringens enzyme and the weakly toxic C. bifermentans phospholipase C.