Immune interferon receptor: chemical and enzymatic sensitivity

Introduction of protein kinase recognition sites into proteins: a review of their preparation, advantages, and applications

Labeled proteins are used in a variety of applications. This review focuses on methods that utilize genetic engineering to introduce protein kinase recognition sites into proteins. Many protein kinase recognition sites can be introduced into proteins and serve as useful tags for a variety of purposes. The introduction of protein kinase recognition sites into proteins can be achieved without modifying the essential structure or function of the proteins. Because proteins modified by these procedures retain their activity after phosphorylation, they can be used in many applications. The phosphorylatable proteins can be labeled easily to high specific activity with radioisotopes ((32)P, (33)P, or (35)S), or the nonradioactive (31)P can be used. The use of these radioisotopes provides a convenient and safe method for radiolabeling proteins. Moreover, the use of the nonradioactive (31)P with protein tyrosine kinase recognition sites permits the tagging of proteins and their detection with the many anti-phosphotyrosine antibodies available. Overall, the procedure represents a convenient, safe, and efficient method to label proteins for a variety of applications.

A novel solid-phase test to study the binding of IFN-gamma to its receptor

A novel solid phase assay for interferon-gamma (IFN-gamma) binding to the human IFN-gamma receptor was developed. The receptor binding assay is carried out using a soluble form of the recombinant IFN-gamma receptor protein corresponding to the extracellular portion of the IFN-gamma receptor. Using different IFN molecules and anti-IFN monoclonal antibodies, we show that the specificity of the soluble IFN-gamma receptor coated to the plastic surface is not altered. In consequence, this new generation binding test can be used to characterize the interactions with the specific ligand under controlled conditions. In comparison with ELISA or RIA tests using antibodies specific for IFN-gamma, the solid-phase binding assay has the advantage of detecting only the active molecules. Finally, since the test has a large capacity, it is being applied for the screening of agents that are able to neutralize the IFN-gamma activity either by blocking the active site of the lymphokine or the binding site of the specific receptor.

Detection and analysis of interferon-alpha receptors on plasma membranes and in detergent extracts

The binding of interferons-alpha (IFN-alpha) to various cells is well characterized, but fewer studies have reported on the interaction of IFN-alpha with receptors on plasma membranes or in detergent-solubilized form. We describe a simple, sensitive, and semiquantitative assay procedure to detect the presence of IFN-alpha receptors on bovine spleen plasma membrane preparations or in detergent-solubilized extracts. The procedure involves spotting the sample on hydrophobic polyvinylidene difluoride (PVDF; Immobilon P) membranes, blocking the filter with milk, and binding radiolabeled IFN-alpha A to the membrane filter, with detection by either autoradiography or scintillation counting. This assay procedure has been applied for the identification of IFN-alpha receptors in crude and affinity-purified fractions. The partially purified IFN-alpha receptors have been further characterized by SDS-polyacrylamide gel electrophoresis (PAGE). The separated IFN-alpha receptor protein on the SDS-PAGE gel has been electrophoretically transferred to Immobilon membrane and visualized by ligand blotting. This provides an estimate of 95-110 kD for the apparent molecular weight and a tool for further studies of the receptor protein.

Molecular characterization of the human interferon-gamma receptor: analysis of polymorphism and glycosylation

Different molecular masses have been assigned to the human interferon-gamma receptor (HuIFN-gamma-R) by several authors. After extensive purification from Raji cells, this receptor was shown in a previous work to consist of two major protein species with molecular masses of 92 kD and 50 kD, as revealed by SDS-PAGE. We show here that the 50-kD band is most probably a degradation product of the 92-kD band due to a trypsin-like protease active during the purification process. The native protein of Raji cells seems, therefore, to have a molecular mass of 92 kD. The same molecular mass was found with Colo 205 cells (derived from a colon carcinoma). However, in conditions where degradation does not occur, the HuIFN-gamma-R shows a certain polymorphism: in IM-9 cells, another B-cell line, two bands exist with molecular masses of 95 kD and 85 kD, and in Wish cells, an amnion-derived cell line, one (or two) band(s) can be detected around 87 kD. This polymorphism is due at least in part to a variable extent of N-glycosylation from line to line and also within the same line, since after tunicamycin treatment of the Raji, IM-9, and Wish cells, very similar bands are obtained with a molecular mass of 72 kD.

Characterization of human interferon-gamma receptor purified from placenta

Membranes prepared from human placenta were used for characterization of the receptor for human interferon-gamma (HuIFN-gamma) after large-scale purification. HuIFN-gamma linked covalently to Affigel-10 was used for the purification of the receptor from octylglucoside-solubilized placental membranes. Radiolabeled IFN-gamma [32P]HuIFN-gamma, was used in binding and cross-linking studies to detect the receptor at different stages of the purification. From binding assays it was calculated that an average placenta contained 90-120 micrograms of receptor with a Kd value of 1.3 x 10(-9) M. Thus, human placenta is a rich and convenient source of receptor for IFN- gamma. When purified receptor was cross-linked to [32P]HuIFN-gamma, a variety of cross-linked bands were detected dependent on the preparation conditions. The use of protease inhibitors in the course of processing prevented degradation of the 90-kD intact receptor, showing that the lower-molecular-weight products detected in previous studies are degradation products of the receptor. Furthermore, a 20-kD fragment of the receptor was found to be active in binding HuIFN-gamma.