The conformational stability of a non-covalent dimer of a platelet-derived growth factor-B mutant lacking the two cysteines involved in interchain disulfide bonds.

Native platelet-derived growth factor-B (PDGF-B) forms a covalent dimer through interchain disulfide bonds. In a previous study, an analog of PDGF-B was produced by replacing cysteine 43 and 52, which are involved in the interchain disulfide bonds, with serine. It was revealed that this analog protein has the dimeric molecule weight at pH 4 to 7, forming a non-covalent dimer in solution, and its mitogenic activity is similar to the native covalent dimer. However, the analog protein was more labile to pepsin digestion and low pH treatment, indicating that the interchain disulfides contribute to the stability of the protein. It is interesting to see if the conformation of the protein is affected by elimination of the interchain disulfide bonds, and if the interchain disulfides play any role in the stability of the protein. Circular dichroism and Fourier transform infrared spectroscopic analyses of the analog showed that it has a conformation similar to the wild type at pH 7.5, but is unfolded at pH 2.5, while the native PDGF-B disulfide-linked dimer shows an apparently unaltered conformation at pH 2.5. The analog is also less stable to sodium dodecylsulfate and guanidine HCl-induced denaturation at neutral pH. These results indicate that the non-covalent interactions are sufficient for proper folding and dimer formation at neutral pH, but that the interchain disulfide bonds greatly stabilize the native conformation of PDGF-B.

Antiviral and antitumor effects of a human interferon analog, IFN-alpha Con 1, assessed in hamsters.

An analog of human alpha-and beta-interferons (IFN-alpha and -beta) (generally consisting of the most frequently observed amino acid residue at each position in the molecule) has pronounced antiviral and antiproliferative activity in human and hamster cells. Intraperitoneal administration of this analog (designated IFN-alpha Con 1) to hamsters at 10(6) to 10(8) U/kg resulted in proportional increases in plasma concentrations through 6 h of monitoring. IFN-alpha Con 1 at these doses effectively limited encephalomyocarditis virus (EMCV) infections of hamsters. A natural human IFN-alpha preparation was also active against virus infections in hamsters. The antitumor activity of IFN-alpha Con 1 and natural human IFN-alpha was assessed in hamsters inoculated with lethal TBD932 lymphosarcoma. Various IFN treatment schedules resulted in prolonged survival following tumor challenge. IFN-alpha Con 1 administered at 10(5) to 10(6) U/hamster daily for 9-12 days following tumor challenge was effective in delaying tumor development, as was a natural human IFN-alpha preparation. The efficacies of combined IFN and cyclophosphamide therapies were determined. Unlike the natural human subtype IFN-alpha A, IFN-alpha Con 1 did not diminish the efficacy of cyclophosphamide (2.5 mg/hamster for 3 days) against the lymphosarcoma. However, an ineffective dose of cyclophosphamide (0.05 mg/hamster for 3 days) when combined with IFN-alpha Con 1 treatment showed enhanced antitumor activity. Combinations of cimetidine (16 mg/hamster for 4 days) and IFN-alpha Con 1 treatment did not prolong survival in this model system.

Protein secretion from Saccharomyces cerevisiae directed by the prepro-alpha-factor leader region.

The Saccharomyces cerevisiae secretory process was studied by evaluating secretion efficiency, processing efficiency, and the efficiency of protein folding for hybrid proteins containing the yeast prepro-alpha-factor leader region. Secretion of three proteins, beta-endorphin, calcitonin, and a consensus alpha-interferon (IFN-Con1), were compared in terms of secretion efficiency into the culture medium, beta-Endorphin and calcitonin, both small proteins, were found to be efficiently secreted from logarithmically grown cells. In contrast, the larger IFN-Con1 accumulated in the periplasmic space and cell wall. The glycosylated, unprocessed prepro-alpha-factor/IFN-Con1 fusion protein was also found to be secreted into the culture medium. The presence of (Glu-Ala) dipeptides in the alpha-factor spacer peptide increased the efficiency of cleavage at Lys-Arg in the prepro-alpha-factor/IFN-Con1 protein fusion. Purified secreted IFN-Con1 was structurally characterized to determine the effect of passage through the yeast secretory pathway on the fidelity and efficiency of protein folding. The disulfide structure of the secreted protein was found to be identical with that reported for the native human alpha-interferons.