Antigenicity analysis of different regions of the severe acute respiratory syndrome coronavirus nucleocapsid protein.
BACKGROUND
The widespread threat of severe acute respiratory syndrome (SARS) to human health has made urgent the development of fast and accurate analytical methods for its early diagnosis and a safe and efficient antiviral vaccine for preventive use. For this purpose, we investigated the antigenicity of different regions of the SARS coronavirus (SARS-CoV) nucleocapsid (N) protein.


METHODS
The cDNA for full-length N protein and its various regions from the SARS-CoV was cloned and expressed in Escherichia coli. After purification, all of the protein fragments were printed on glass slides to fabricate a protein microarray and then probed with the sera from SARS patients to determine the reactivity of these protein fragments.


RESULTS
The full-length protein and two other fragments reacted with all 52 sera tested. Four important regions with possible epitopes were identified and named as EP1 (amino acids 51-71), EP2 (134-208), EP3 (249-273), and EP4 (349-422), respectively. EP2 and EP4 possessed linear epitopes, whereas EP1 and EP2 were able to form conformational epitopes that could react with most (>80%) of the tested sera. EP3 and EP4 also formed conformational epitopes, and antibodies against these epitopes existed in all 52 of the sera tested.


CONCLUSIONS
The N protein is a highly immunogenic protein of the SARS-CoV. Conformational epitopes are important for this protein, and antigenicity of the COOH terminus is higher than that of the NH(2) terminus. The N protein is a potential diagnostic antigen and vaccine candidate for SARS-CoV.
Chen
Zeliang
Z
Institute of Microbiology and Epidemiology, Academy of Military Medical Sciences, Beijing 100071, China.
Pei
Decui
D
Jiang
Lingxiao
L
Song
Yajun
Y
Wang
Jin
J
Wang
Hongxia
H
Zhou
Dongsheng
D
Zhai
Junhui
J
Du
Zongmin
Z
Li
Bei
B
Qiu
Maofeng
M
Han
Yanping
Y
Guo
Zhaobiao
Z
Yang
Ruifu
R
D000956:Antigens, Viral / Q000235:genetics / Q000276:immunology*; D003001:Cloning, Molecular; D000086462:Coronavirus Nucleocapsid Proteins; D018076:DNA, Complementary / Q000235:genetics; D000939:Epitopes; D004926:Escherichia coli / Q000378:metabolism; D006801:Humans; D019590:Nucleocapsid Proteins / Q000096:biosynthesis / Q000235:genetics / Q000276:immunology*; D040081:Protein Array Analysis; D045473:Severe acute respiratory syndrome-related coronavirus / Q000276:immunology* / Q000302:isolation & purification; D045169:Severe Acute Respiratory Syndrome / Q000175:diagnosis
D000956:Antigens, Viral; D000086462:Coronavirus Nucleocapsid Proteins; D018076:DNA, Complementary; D000939:Epitopes; D019590:Nucleocapsid Proteins