Improving the soluble expression of recombinant proteins by randomly shuffling 5' and 3' coding-sequence ends

Viral Macro Domains Reverse Protein ADP-Ribosylation

ADP-ribosylation is a posttranslational protein modification in which ADP-ribose is transferred from NAD(+) to specific acceptors to regulate a wide variety of cellular processes. The macro domain is an ancient and highly evolutionarily conserved protein domain widely distributed throughout all kingdoms of life, including viruses. The human TARG1/C6orf130, MacroD1, and MacroD2 proteins can reverse ADP-ribosylation by acting on ADP-ribosylated substrates through the hydrolytic activity of their macro domains. Here, we report that the macro domain from hepatitis E virus (HEV) serves as an ADP-ribose-protein hydrolase for mono-ADP-ribose (MAR) and poly(ADP-ribose) (PAR) chain removal (de-MARylation and de-PARylation, respectively) from mono- and poly(ADP)-ribosylated proteins, respectively. The presence of the HEV helicase in cis dramatically increases the binding of the macro domain to poly(ADP-ribose) and stimulates the de-PARylation activity. Abrogation of the latter dramatically decreases replication of an HEV subgenomic replicon. The de-MARylation activity is present in all three pathogenic positive-sense, single-stranded RNA [(+)ssRNA] virus families which carry a macro domain: Coronaviridae (severe acute respiratory syndrome coronavirus and human coronavirus 229E), Togaviridae (Venezuelan equine encephalitis virus), and Hepeviridae (HEV), indicating that it might be a significant tropism and/or pathogenic determinant.

IMPORTANCE

Protein ADP-ribosylation is a covalent posttranslational modification regulating cellular protein activities in a dynamic fashion to modulate and coordinate a variety of cellular processes. Three viral families, Coronaviridae, Togaviridae, and Hepeviridae, possess macro domains embedded in their polyproteins. Here, we show that viral macro domains reverse cellular ADP-ribosylation, potentially cutting the signal of a viral infection in the cell. Various poly(ADP-ribose) polymerases which are notorious guardians of cellular integrity are demodified by macro domains from members of these virus families. In the case of hepatitis E virus, the adjacent viral helicase domain dramatically increases the binding of the macro domain to PAR and simulates the demodification activity.

Structural characterization of the N-terminal part of the MERS-CoV nucleocapsid by X-ray diffraction and small-angle X-ray scattering

The N protein of coronaviruses is a multifunctional protein that is organized into several domains. The N‐terminal part is composed of an intrinsically disordered region (IDR) followed by a structured domain called the N‐terminal domain (NTD). In this study, the structure determination of the N‐terminal region of the MERS‐CoV N protein via X‐ray diffraction measurements is reported at a resolution of 2.4 Å. Since the first 30 amino acids were not resolved by X‐ray diffraction, the structural study was completed by a SAXS experiment to propose a structural model including the IDR. This model presents the N‐terminal region of the MERS‐CoV as a monomer that displays structural features in common with other coronavirus NTDs.