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J. Virol. doi:10.1128/JVI.02612-07
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Without its N-Finger, SARS-CoV Main Protease can Form a Novel Dimer through its C-Terminal Domain

From Beijing Nuclear Magnetic Resonance Center, College of Chemistry and Molecular Engineering, and College of Life Science, Peking University, Beijing 100871, China

^* To whom correspondence should be addressed. Email: binxia{at}pku.edu.cn.

	Abstract

The main protease (M^pro) of severe acute respiratory syndrome coronavirus (SARS-CoV) plays an essential role in the extensive proteolytic processing of the viral polyproteins (pp1a and pp1ab), and it is an important target for anti-SARS drug development. It was found that SARS-CoV M^pro exists in solution as equilibrium of both monomeric and dimeric forms, and the dimeric form is the enzymatically active form. However, the mechanism of SARS-CoV M^pro dimerization, especially the roles of its N-terminal seven residues (N-finger) and its unique C-terminal domain in the dimerization, remain unclear. Here, we report that SARS-CoV M^pro C-terminal domain alone (residues 187-306, M^pro-C) is produced in E. coli in both monomeric and dimeric forms, and no exchange could be observed between them at room temperature. The M^pro-C dimer has a novel dimerization interface. Meanwhile, the N-finger deletion mutant of SARS-CoV M^pro also exists as both stable monomer and stable dimer, and the dimer is formed through the same C-terminal domain interaction as that in the M^pro-C dimer. However, no C-terminal domain mediated dimerization form can be detected for the wild-type SARS-CoV M^pro. Our study results help to clarify previously published controversial claims about the role of N-finger in SARS-CoV M^pro dimerization. Apparently, without the N-finger, SARS-CoV M^pro can no longer retain the active dimer structure; instead it can form a new-type of dimer which is inactive. Therefore, the N-finger of SARS-CoV M^pro is not only critical for its dimerization, but also essential for the enzyme to form the enzymatically active dimer.