We are currently witnessing a major epidemic caused by the 2019 novel coronavirus (2019-nCoV). The evolution of 2019-nCoV remains elusive. We found 4 insertions in the spike glycoprotein (S) which are unique to the 2019-nCoV and are not present in other coronaviruses. Importantly, amino acid residues in all the 4 inserts have identity or similarity to those in the HIV-1 gp120 or HIV-1 Gag. Interestingly, despite the inserts being discontinuous on the primary amino acid sequence, 3D-modelling of the 2019-nCoV suggests that they converge to constitute the receptor binding site. The finding of 4 unique inserts in the 2019-nCoV, all of which have identity /similarity to amino acid residues in key structural proteins of HIV-1 is unlikely to be fortuitous in nature. This work provides yet unknown insights on 2019-nCoV and sheds light on the evolution and pathogenicity of this virus with important implications for diagnosis of this virus.

One of the most intriguing disease-related mutations in human prion protein (PrP) is the Tyr to Stop codon substitution at position 145. This mutation results in a Gerstmann-Straussler-Scheinkerlike disease with extensive PrP amyloid deposits in the brain. Here, we provide evidence for a spontaneous conversion of the recombinant polypeptide corresponding to the Y145Stop variant (huPrP23-144) from a monomeric unordered state to a fibrillar form. This conversion is characterized by a protein concentration-dependent lag phase and has characteristics of a nucleation-dependent polymerization. Atomic force microscopy shows that huPrP23-144 fibrils are characterized by an apparent periodicity along the long axis, with an average period of 20 nm. Fourier-transform infrared spectra indicate that the conversion is associated with formation of ␤-sheet structure. However, the infrared bands for huPrP23-144 are quite different from those for a synthetic peptide PrP106 -126, suggesting conformational non-equivalence of ␤-structures in the disease-associated Y145Stop variant and a frequently used short model peptide. To identify the region that is critical for the self-seeded assembly of huPrP23-144 amyloid, experiments were performed by using the recombinant polypeptides corresponding to prion protein fragments 23-114, 23-124, 23-134, 23-137, 23-139, and 23-141. Importantly, none of the fragments ending before residue 139 showed a propensity for conformational conversion to amyloid fibrils, indicating that residues within the 138 -141 region are essential for this conversion.

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The principal infectious and pathogenic agent in all prion disorders is a beta-sheet-rich isoform of the cellular prion protein (PrP(C)) termed PrP-scrapie (PrP(Sc)). Once initiated, PrP(Sc) is self-replicating and toxic to neuronal cells, but the underlying mechanisms remain unclear. In this report, we demonstrate that PrP(C) binds iron and transforms to a PrP(Sc)-like form (*PrP(Sc)) when human neuroblastoma cells are exposed to an inorganic source of redox iron. The *PrP(Sc) thus generated is itself redox active, and it induces the transformation of additional PrP(C), simulating *PrP(Sc) propagation in the absence of brain-derived PrP(Sc). Moreover, limited depletion of iron from prion disease-affected human and mouse brain homogenates and scrapie-infected mouse neuroblastoma cells results in 4- to 10-fold reduction in proteinase K (PK)-resistant PrP(Sc), implicating redox iron in the generation, propagation, and stability of PK-resistant PrP(Sc). Furthermore, we demonstrate increased redox-active ferrous iron levels in prion disease-affected brains, suggesting that accumulation of PrP(Sc) is modulated by the combined effect of imbalance in brain iron homeostasis and the redox-active nature of PrP(Sc). These data provide information on the mechanism of replication and toxicity by PrP(Sc), and they evoke predictable and therapeutically amenable ways of modulating PrP(Sc) load.

We report studies on an L-asparaginase from Pyrococcus furiosus, cloned and expressed in Escherichia coli and purified to homogeneity. Protein stability and enzyme kinetic parameters were determined. The enzyme was found to be thermostable, natively dimeric, and glutaminase-free, with optimum activity at pH 9.0. It showed a K(m) of 12 mM and a substrate inhibition profile above 20 mM L-asparagine. Urea could not induce unfolding and enzyme inactivation; however, with guanidine hydrochloride (GdnCl) a two-state unfolding pattern was observed. Reduced activity and an altered near-UV-CD signal for protein at low GdnCl concentration (1 M) suggested tertiary structural changes at the enzyme active site. A homology three-dimensional model was developed and the structural information was combined with activity and stability data to give functional clues about the asparaginase.