The Structural Characterization and Antigenicity of the S Protein of SARS-CoV

The corona-like spikes or peplomers on the surface of the virion under electronicmicroscope are the most striking features of coronaviruses. The S (spike) proteinis the largest structural protein, with 1,255 amino acids, in the viral genome. Itsstructure can be divided into three regions: a long N-terminal region in the exte-rior, a characteristic transmembrane (TM) region, and a short C-terminus in theinterior of a virion. We detected fifteen substitutions of nucleotides by comparisonswith the seventeen published SARS-CoV genome sequences, eight (53.3%) of whichare non-synonymous mutations leading to amino acid alternations with predictedphysiochemical changes. The possible antigenic determinants of the S protein arepredicted, and the result is confirmed by ELISA (enzyme-linked immunosorbentassay) with synthesized peptides. Another profound finding is that three disulfidebonds are defined at the C-terminus with the N-terminus of the E (envelope) pro-tein, based on the typical sequence and positions, thus establishing the structuralconnection with these two important structural proteins, if confirmed. Phyloge-netic analysis reveals several conserved regions that might be potent drug targets.

The Structure Analysis and Antigenicity Study of the N Protein of SARS-CoV

The Coronaviridae family is characterized by a nucleocapsid that is composed of thegenome RNA molecule in combination with the nucleoprotein (N protein) withina virion. The most striking physiochemical feature of the N protein of SARS-CoVis that it is a typical basic protein with a high predicted pI and high hydrophilicity,which is consistent with its function of binding to the ribophosphate backbone ofthe RNA molecule. The predicted high extent of phosphorylation of the N proteinon multiple candidate phosphorylation sites demonstrates that it would be relatedto important functions, such as RNA-binding and localization to the nucleolus ofhost cells. Subsequent study shows that there is an SR-rich region in the N proteinand this region might be involved in the protein-protein interaction. The abundantantigenic sites predicted in the N protein, as well as experimental evidence withsynthesized polypeptides, indicate that the N protein is one of the major antigensof the SARS-CoV. Compared with other viral structural proteins, the low variationrate of the N protein with regards to its size suggests its importance to the survivalof the virus.

The E Protein Is a Multifunctional Membrane Protein of SARS-CoV

The E (envelope) protein is the smallest structural protein in all coronaviruses andis the only viral structural protein in which no variation has been detected. Weconducted genome sequencing and phylogenetic analyses of SARS-CoV. Based ongenome sequencing, we predicted the E protein is a transmembrane (TM) pro-tein characterized by a TM region with strong hydrophobicity and α-helix con-formation. We identified a segment (NH2-_L-Cys-A-Y-Cys-Cys-N_-COOH) in thecarboxyl-terminal region of the E protein that appears to form three disulfide bondswith another segment of corresponding cysteines in the carboxyl-terminus of the S(spike) protein. These bonds point to a possible structural association between theE and S proteins. Our phylogenetic analyses of the E protein sequences in all pub-lished coronaviruses place SARS-CoV in an independent group in Coronaviridaeand suggest a non-human animal origin.

Complete Genome Sequences of the SARS-CoV: the BJ Group (Isolates BJ01-BJ04)

Beijing has been one of the epicenters attacked most severely by the SARS-CoV (severe acute respiratory syndrome-associated coronavirus) since the first patient was diagnosed in one of the city's hospitals. We now report complete genome sequences of the BJ Group, including four isolates (Isolates B J01, B J02, B J03,and B J04) of the SARS-CoV. It is remarkable that all members of the BJ Group share a common haplotype, consisting of seven loci that differentiate the group from other isolates published to date. Among 42 substitutions uniquely identifled from the BJ group, 32 are non-synonymous changes at the amino acid level.Rooted phylogenetic trees, proposed on the basis of haplotypes and other sequence variations of SARS-CoV isolates from Canada, USA, Singapore, and China, gave rise to different paradigms but positioned the BJ Group, together with the newly discovered GD01 (GD-Ins29) in the same clade, followed by the H-U Group (from Hong Kong to USA) and the H-T Group (from Hong Kong to Toronto), leaving the SP Group (Singapore) more distant. This result appears to suggest a possible transmission path from Guangdong to Beijing/Hong Kong, then to other countries and regions.