Glutathione peroxidases (GPX), a family of antioxidant selenoenzymes, functionally link selenium and glutathione, which both show correlations with clinical outcomes in COVID-19. Thus, it is highly significant that cytosolic GPX1 has been shown to interact with an inactive C145A mutant of M pro , the main cysteine protease of SARS-CoV-2, but not with catalytically active wild-type M pro . This seemingly anomalous result is what might be expected if GPX1 is a substrate for the active protease, leading to its fragmentation. We show that the GPX1 active site sequence is substantially similar to a known M pro cleavage site, and is identified as a potential cysteine protease site by the Procleave algorithm. Proteolytic knockdown of GPX1 is highly consistent with previously documented effects of recombinant SARS-CoV M pro in transfected cells, including increased reactive oxygen species and NF-κB activation. Because NF-κB in turn activates many pro-inflammatory cytokines, this mechanism could contribute to increased inflammation and cytokine storms observed in COVID-19. Using web-based protease cleavage site prediction tools, we show that M pro may be targeting not only GPX1, but several other selenoproteins including SELENOF and thioredoxin reductase 1, as well as glutamate-cysteine ligase, the rate-limiting enzyme for glutathione synthesis. This hypothesized proteolytic knockdown of components of both the thioredoxin and glutaredoxin systems is consistent with a viral strategy to inhibit DNA synthesis, to increase the pool of ribonucleotides for RNA synthesis, thereby enhancing virion production. The resulting “collateral damage” of increased oxidative stress and inflammation would be exacerbated by dietary deficiencies of selenium and glutathione precursors.
The level of calmodulin increases in cells expressing HIV-1 envelope glycoprotein. Although a calmodulin increase is bound to alter many cellular metabolic and signaling pathways, the benefits to the virus of these alterations must be indirect. However, the possibility exists that increased cellular calmodulin benefits the virus by directly associating with nonenvelope viral proteins. We have, therefore, investigated whether calmodulin can interact with HIV structural proteins Gag, p17, and p24. Calmodulin binds Gag and p17 but not p24 in (125)I-labeled calmodulin overlays of SDS-polyacrylamide gels. Removal of calcium by addition of EGTA eliminates this binding. A computer algorithm for predicting helical regions that should bind calmodulin predicts that there are two calmodulin-binding regions near the N terminus of p17. Intrinsic tryptophan fluorimetry shows that two peptides, each of which includes one of the predicted regions, bind calmodulin: p17(11-25) binds calmodulin with a 2-to-1 stoichiometry and dissociation constant of approximately 10(-9) M(2), and p17(31-46) also binds calmodulin with a dissociation constant of about 10(-9) M. These binding sites are nearly contiguous, forming an extended calmodulin-binding domain p17(11-46). In H-9 cells, Gag and calmodulin colocalize within the resolution of confocal light microscopy.
Cross-linked protein crystals represent a new class of micro-and mesoporous materials with properties potentially useful in technologies as diverse as chiral separations and drug delivery. These applications require the generation of protein crystals in formats and sizes quite distinct from the traditional submillimeter single crystals favored by structural biologists. Here we report a high-yield method for forming monodisperse protein crystals with tunable dimensions ranging from 250 nm up to tens of micrometers. X-ray powder diffraction of these crystallites confirms that the hen egg white lysozyme crystals are identical in structure to that of the bulk tetragonal lysozyme (a ) 79.05 Å; c ) 37.96 Å).
Several marine fishes from both the Arctic and Antarctic have serum macromolecules that protect them from freezing.14 Of the four macromolecules thus far isolated, two are glycoproteins with similar composition and two are proteins, also with similar compo~ition.~ At physiological concentrations, each of these "antifreezes" lowers the freezing point of water by roughly 1°C in the presence of an ice seed crystal, but does not significantly lower the melting point.The adsorption of macromolecules on solid surfaces is a well-known phenomenons7 and in many cases can inhibit crystal growth.8
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