Enzyme immunoassay of 2'-5'-oligoadenylates at the femtomole level

The Galactose-Specific Lectin from the Sponge Chondrilla Nucula Displays Anti-Human Immunodeficiency Virus Activity in vitro via Stimulation of the (2′-5′)Oligoadenylate Metabolism

A new lectin has been isolated from the sponge Chondrilla nucula. The purified CN lectin is a protein composed of four polypeptide chains with a molecular weight (MW) of 15600. The isoelectric point is 4.5 and the amino acid composition is rich in aspartic and glutamic acid. The lectin precipitates erythrocytes from humans (A, B, O) with a titre between 25 and 210. The CN lectin is d-galactose-specific and displays a moderate mitogenic effect on spleen lymphocytes from mice and on CD4-positive human H9 cells. An interesting feature of this lectin is its ability to stimulate the (2′-5′)oligoriboadenylate [(2′-5′)A] metabolic pathway in non-infected and human immunodeficiency virus (HIV-1)-infected H9 cells. Moreover, HIV-1-infected H9 cells show an increase in the time period of HIV-1 release in response to CN lectin treatment. These data suggest that CN lectin causes a retardation of HIV-1 release due to further increase of the elevated intracellular level of (2′-5′)A.

Preparation of a conjugate of 2',5'-triadenylate 5'-triphosphate and biotinylated firefly luciferase and its use for sensitive bioluminescent enzyme immunoassay

A bioluminescent enzyme immunoassay (BLEIA) for 2',5'-oligoadenylate 5'-triphosphate (pppA2'p5'A2'Ap5'A, 2-5A) was developed using a conjugate of 2-5A and firefly luciferase as a probe. The conjugate was prepared from a 2-5A derivative bearing a thiol group at the 2'(or 3') end, and streptavidin (SA) bearing maleimide via a linker-arm and biotinylated luciferase. The thiol group of the 2-5A derivative was relatively stable under aerobic conditions and remained 100% and 56% intact at 25 degrees C after 1 and 96 h, respectively, without dimerization by aerobic oxidation. The thiol-modified 2-5A was coupled with the SA-maleimide conjugate, followed by complex formation with biotinylated firefly luciferase. BLEIA using this conjugate allowed for the direct analysis of 2-5A in a range of 5-500 fmol (0.1-10 nM in a 50 microL sample) and in a reaction time of 15 min. The measurement of microquantities of 2-5 A from various sources is easy to perform by this BLEIA, because no radioisotope labeled 2-5A was required as a probe.

The 2-5A system: modulation of viral and cellular processes through acceleration of RNA degradation

The 2-5A system is an RNA degradation pathway that can be induced by the interferons (IFNs). Treatment of cells with IFN activates genes encoding several double-stranded RNA (dsRNA)-dependent synthetases. These enzymes generate 5'-triphosphorylated, 2',5'-phosphodiester-linked oligoadenylates (2-5A) from ATP. The effects of 2-5A in cells are transient since 2-5A is unstable in cells due to the activities of phosphodiesterase and phosphatase. 2-5A activates the endoribonuclease 2-5A-dependent RNase L, causing degradation of single-stranded RNA with moderate specificity. The human 2-5A-dependent RNase is an 83.5 kDa polypeptide that has little, if any, RNase activity, unless 2-5A is present. 2-5A binding to RNase L switches the enzyme from its off-state to its on-state. At least three 2',5'-linked oligoadenylates and a single 5'-phosphoryl group are required for maximal activation of the RNase. Even though the constitutive presence of 2-5A-dependent RNase is observed in nearly all mammalian cell types, cellular amounts of 2-5A-dependent mRNA and activity can increase after IFN treatment. One well-established role of the 2-5A system is as a host defense against some types of viruses. Since virus infection of cells results in the production and secretion of IFNs, and since dsRNA is both a frequent product of virus infection and an activator of 2-5A synthesis, the replication of encephalomyocarditis virus, which produces dsRNA during its life cycle, is greatly suppressed in IFN-treated cells as a direct result of RNA decay by the activated 2-5A-dependent RNase. This review covers the organic chemistry, enzymology, and molecular biology of 2-5A and its associated enzymes. Additional possible biological roles of the 2-5A system, such as in cell growth and differentiation, human immunodeficiency virus replication, heat shock, atherosclerotic plaque, pathogenesis of Type I diabetes, and apoptosis, are presented.