sars2

The Spike (S) protein, or sars2, is the most conspicuous structural protein in SARS virion. It binds its host cell receptor, angiotensin-converting enzyme 2 (ACE-2) via its N-terminal S1 domain and mediates the fusion of viral and host membranes. Both processes are essential for viral infection of the host cell as evidenced by membrane fusion and viral infectivity being specifically inhibited by a fragment containing the receptor binding domain or by antibodies against ACE-2 or the receptor binding domain.  The C-terminal domain of the SARS S protein contains two “heptad repeat” regions, HR1 and HR2, which associate into anti-parallel six-helix bundles, as several recent structures have revealed.

Membrane fusion occurs when conformational changes in the HR1–HR2 structure bring the fusion peptide near the N-terminus of HR1 proximal to the transmembrane domain . The mechanism of membrane fusion offers yet another attractive drug target. HR1 and HR2 peptides themselves are effective at inhibiting viral replication in cultured cells and can guide the design of peptidomimetics and small molecules that also interfere in the formation of the fusion core. The S protein is also significant from the standpoint of vaccine development. Antibodies to S are found in patient sera, and more importantly neutralize the virus. In the mouse model, they have been shown to provide protective passive immunity and a DNA vaccine encoding S also induce T cell and antibody responses and likewise protect mice from SARS-CoV infection . Tunicamycin treatment induces misfolding of the spike protein, and leads to the formation of spike-depleted virions. The spike and nucleoprotein are organized in overlapping, orthorhombic, paracrystalline lattices. The spacing of spike is apparently determined by the arrangement of the underlying proteins, matrix and nucleocapsid. Based on actual observations of spike proteins, as well as size and volume measurements, the molecule appears to be trimeric.  

 

Li F, Li W, Farzan M, Harrison SC. Structure of SARS coronavirus spike receptor-binding domain complexed with receptor. Science. 2005 Sep 16;309(5742):1864-8.

Li W, Moore MJ, Vasilieva N, Sui J, Wong SK, Berne MA, Somasundaran M, Sullivan JL, Luzuriaga K, Greenough TC, Choe H, Farzan M. Angiotensin-converting enzyme 2 is a functional receptor for the SARS coronavirus. Nature. 2003 Nov 27;426(6965):450-4.

X. Xiao, S. Chakraborti, A.S. Dimitrov, K. Gramatikoff and D.S. Dimitrov, The SARS-CoV S glycoprotein: expression and functional characterization, Biochem. Biophys. Res. Commun. 312 (2003), pp. 1159–1164.

G.J. Babcock, D.J. Esshaki, W.D. Thomas Jr. and D.M. Ambrosino, Amino acids 270 to 510 of the severe acute respiratory syndrome coronavirus spike protein are required for interaction with receptor, J. Virol. 78 (2004), pp. 4552–4560.

S.K. Wong, W. Li, M.J. Moore, H. Choe and M.A. Farzan, 193-amino acid fragment of the SARS coronavirus S protein efficiently binds angiotensin-converting enzyme 2, J. Biol. Chem. 279 (2004), pp. 3197–3201.

T.M. Gallagher and M.J. Buchmeier, Coronavirus spike proteins in viral entry and pathogenesis, Virology 279 (2001), pp. 371–374.

S.K. Wong, W. Li, M.J. Moore, H. Choe and M.A. Farzan, 193-amino acid fragment of the SARS coronavirus S protein efficiently binds angiotensin-converting enzyme 2, J. Biol. Chem. 279 (2004), pp. 3197–3201.

J. Sui, W. Li, A. Murakami, A. Tamin, L.J. Matthews, S.K. Wong, M.J. Moore, A.S. Tallarico, M. Olurinde, H. Choe, L.J. Anderson, W.J. Bellini, M. Farzan and W.A. Marasco, Potent neutralization of severe acute respiratory syndrome (SARS) coronavirus by a human mAb to S1 protein that blocks receptor association, Proc. Natl. Acad. Sci. U.S.A. 101 (2004), pp. 2536–2541.

C.-F. Chou, S. Shen, Y.-J. Tan, B.C. Fielding, T.H.P. Tan, J. Fu, Q. Xu, S.G. Lim and W. Hong, A novel cell-based binding assay system reconstituting interaction between SARS-CoV S protein and its cellular receptor, J. Virol. Methods 123 (2004), pp. 41–48.

Prabakaran P, Gan J, Feng Y, Zhu Z, Choudhry V, Xiao X, Ji X, Dimitrov DS. Structure of severe acute respiratory syndrome coronavirus receptor-binding domain complexed with neutralizing antibody. J Biol Chem. 2006 Jun 9;281(23):15829-36. Epub 2006 Apr 5.

Duquerroy S, Vigouroux A, Rottier PJ, Rey FA, Bosch BJ. Central ions and lateral asparagine/glutamine zippers stabilize the post-fusion hairpin conformation of the SARS coronavirus spike glycoprotein. Virology. 2005 May 10;335(2):276-85.

Supekar VM, Bruckmann C, Ingallinella P, Bianchi E, Pessi A, Carfi A. Structure of a proteolytically resistant core from the severe acute respiratory syndrome coronavirus S2 fusion protein. Proc Natl Acad Sci U S A. 2004 Dec 28;101(52):17958-63. Epub 2004 Dec 16.

Hakansson-McReynolds S, Jiang S, Rong L, Caffrey M. Solution structure of the severe acute respiratory syndrome-coronavirus heptad repeat 2 domain in the prefusion state. J Biol Chem. 2006 Apr 28;281(17):11965-71. Epub 2006 Feb 28.

Sainz B Jr, Rausch JM, Gallaher WR, Garry RF, Wimley WC. Identification and characterization of the putative fusion peptide of the severe acute respiratory syndrome-associated coronavirus spike protein. J Virol. 2005 Jun;79(11):7195-206.

B.J. Bosch, B.E. Martina, R. Van Der Zee, J. Lepault, B.J. Haijema, C. Versluis, A.J. Heck, R. De Groot, A.D. Osterhaus and P.J. Rottier, Severe acute respiratory syndrome coronavirus (SARS-CoV) infection inhibition using spike protein heptad repeat-derived peptides, Proc. Natl. Acad. Sci. U.S.A. 101 (2004), pp. 8455–8460.

S. Liu, G. Xiao, Y. Chen, Y. He, J. Niu, C.R. Escalante, H. Xiong, J. Farmar, A.K. Debnath, P. Tien and S. Jiang, Interaction between heptad repeat 1 and 2 regions in spike protein of SARS-associated coronavirus: implications for virus fusogenic mechanism and identification of fusion inhibitors, Lancet 363 (2004), pp. 938–947.

K. Yuan, L. Yi, J. Chen, X. Qu, T. Qing, X. Rao, P. Jiang, J. Hu, Z. Xiong, Y. Nie, X. Shi, W. Wang, C. Ling, X. Yin, K. Fan, L. Lai, M. Ding and H. Deng, Suppression of SARS-CoV entry by peptides corresponding to heptad regions on spike glycoprotein, Biochem. Biophys. Res. Commun. 319 (2004), pp. 746–752.

J. Zhu, G. Xiao, Y. Xu, F. Yuan, C. Zheng, Y. Liu, H. Yan, D.K. Cole, J.I. Bell, Z. Rao, P. Tien and G.F. Gao, Following the rule: formation of the 6-helix bundle of the fusion core from severe acute respiratory syndrome coronavirus spike protein and identification of potent peptide inhibitors, Biochem. Biophys. Res. Commun. 319 (2004), pp. 283–288.

Xu Y, Lou Z, Liu Y, Pang H, Tien P, Gao GF, Rao Z. Crystal structure of severe acute respiratory syndrome coronavirus spike protein fusion core. J Biol Chem. 2004 Nov 19;279(47):49414-9. Epub 2004 Sep 1.