Yeast expression and characterization of SARS-CoV N protein

SARS-CoV-2: Origin, Evolution, and Targeting Inhibition

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) caused an outbreak in Wuhan city, China and quickly spread worldwide. Currently, there are no specific drugs or antibodies that claim to cure severe acute respiratory diseases. For SARS-CoV-2, the spike (S) protein recognizes and binds to the angiotensin converting enzyme 2 (ACE2) receptor, allowing viral RNA to enter the host cell. The main protease (Mpro) is involved in the proteolytic process for mature non-structural proteins, and RNA-dependent RNA polymerase (RdRp) is responsible for the viral genome replication and transcription processes. Owing to the pivotal physiological roles in viral invasion and replication, S protein, Mpro, RdRp are regarded as the main therapeutic targets for coronavirus disease 2019 (COVID-19). In this review, we carried out an evolutionary analysis of SARS-CoV-2 in comparison with other mammal-infecting coronaviruses that have sprung up in the past few decades and described the pathogenic mechanism of SARS-CoV-2. We displayed the structural details of S protein, Mpro, and RdRp, as well as their complex structures with different chemical inhibitors or antibodies. Structural comparisons showed that some neutralizing antibodies and small molecule inhibitors could inhibit S protein, Mpro, or RdRp. Moreover, we analyzed the structural differences between SARS-CoV-2 ancestral S protein and D614G mutant, which led to a second wave of infection during the recent pandemic. In this context, we outline the methods that might potentially help cure COVID-19 and provide a summary of effective chemical molecules and neutralizing antibodies.

Overview of lethal human coronaviruses

Coronavirus infections of multiple origins have spread to date worldwide, causing severe respiratory diseases. Seven coronaviruses that infect humans have been identified: HCoV-229E, HCoV-OC43, HCoV-NL63, HCoV-HKU1, SARS-CoV, MERS-CoV, and SARS-CoV-2. Among them, SARS-CoV and MERS-CoV caused outbreaks in 2002 and 2012, respectively. SARS-CoV-2 (COVID-19) is the most recently discovered. It has created a severe worldwide outbreak beginning in late 2019, leading to date to over 4 million cases globally. Viruses are genetically simple, yet highly diverse. However, the recent outbreaks of SARS-CoV and MERS-CoV, and the ongoing outbreak of SARS-CoV-2, indicate that there remains a long way to go to identify and develop specific therapeutic treatments. Only after gaining a better understanding of their pathogenic mechanisms can we minimize viral pandemics. This paper mainly focuses on SARS-CoV, MERS-CoV, and SARS-CoV-2. Here, recent studies are summarized and reviewed, with a focus on virus-host interactions, vaccine-based and drug-targeted therapies, and the development of new approaches for clinical diagnosis and treatment.

Expression of SARS-coronavirus spike glycoprotein in Pichia pastoris

To establish a rapid and economical method for the expression of viral proteins in high yield and purity by Pichia pastoris, the S protein of the SARS-CoV was selected in this study. Six S glycoprotein fragments were expressed in Escherichiacoli BL21 and yeast KM71H strains. After purification by affinity chromatography, the protein identities were confirmed by western blot analysis, N-terminal sequencing and mass spectrometry. The proteins expressed in E. coli were low in solubility and bound by GroEL. They still formed soluble aggregates even when the GroEL was removed by urea. The proteins expressed in P. pastoris were relatively soluble. The maximal yield of the RBD reached 46 mg/l with purity greater than 95%. Pull-down assay revealed that ACE2 was specifically captured from cell lysate, indicating that the RBD was biologically active. The glycosylated and deglycosylated RBD was then subjected to SEC and results showed that deglycosylated RBD formed soluble aggregates again. Taken together, pure and biological active RBD of the S protein could be expressed in P. pastoris, and the P. pastoris expression platform will be a good alternative for the expression of viral proteins, in particular, the highly glycosylated surface proteins that mediate the tissue tropism and viral entry.

Copious production of SARS-CoV nucleocapsid protein employing codon optimized synthetic gene

The severe acute respiratory syndrome coronavirus (SARS-CoV) nucleocapsid protein (NP) is one of the predominant antigenic protein and the most abundant shed antigen throughout the SARS-CoV infection. This feature makes it a suitable molecular target for diagnostic applications. In this study the full length codon optimized NP gene and its subfragment gene segment was cloned in a bacterial expression vector. The full length NP could be expressed in E. coli at very high level within inclusion bodies. The inclusion bodies were successfully solubilized, purified under denaturing conditions employing IMAC column and refolded. The non-glycosylated NP was used to immunize mice for hybridoma development. The polyclonal antiserum from animals immunized with this recombinant NP protein was found to specifically recognize the NP and its subfragments, thus demonstrating the immunogenic nature of the recombinant protein. The NP antigen or a subfragment could be useful for developing a sensitive serum diagnostic assay to monitor SARS-CoV outbreaks by detecting the early human anti-SARS antibodies. In addition, the availability of the NP fragments could facilitate epitope mapping of anti-NP monoclonals for identifying suitable sandwich pairs.