Characterization of human coronavirus OC43 nucleocapsid protein

Abstract

The primary function of human coronavirus OC43 nucleocapsid protein (HCoV-OC43 N protein) is to recognize a stretch of RNA that serves as a packaging signal leading to the formation of the ribonucleoprotein (RNP) complex during assembly. In this study, we have analyzed the biochemical and stability properties of the recombinant HCoV-OC43 N protein. The nucleic acid-binding activity was identified by band-shift assay and the results showed that HCoV-OC43 N protein interacts to DNA and RNA in a nonspecific way. According to the cross-linking analysis, HCoV-OC43 N protein forms higher multimers that were composed of individual dimers as a building block. Electrostatic interactions were believed to take part in the stabilization of compact conformation of HCoV-OC43 N protein. The results of conformation analyses obtained from circular dichroism (CD) spectra showed that HCoV-OC43 N protein contains approximately 35.1% alpha-helix, 11.6% beta-sheet, 23.8% turn, and 29.5% random coil. Heat and urea-induced denaturation analyses indicated that Tm and Cm (the denaturant molarity at the midpoint of the transition) of HCoV-OC43 N protein were 52 ¢XC and 4 M, respectively. Acid-induced denaturation showed that N protein started to denature near pH5.7, and was fully denatured at pH 2.9. Our results suggest that HCoV-OC43 N protein is more stable than SARS N protein studied previously.