Receptor-binding domain of severe acute respiratory syndrome coronavirus spike protein contains multiple conformation-dependent epitopes that induce highly potent neutralizing antibodies.
The spike (S) protein of severe acute respiratory syndrome associated coronavirus (SARS-CoV) is a major antigenic determinant capable of inducing protective immunity. Recently, a small fragment on the SARS-CoV S protein (residues 318-510) was characterized as a minimal receptor-binding domain (RBD), which mediates virus binding to angiotensin-converting enzyme 2, the functional receptor on susceptible cells. In this study, we demonstrated that a fusion protein containing RBD linked to human IgG1 Fc fragment (designated RBD-Fc) induced high titer of RBD-specific Abs in the immunized mice. The mouse antisera effectively neutralized infection by both SARS-CoV and SARS pseudovirus with mean 50% neutralization titers of 1/15,360 and 1/24,737, respectively. The neutralization determinants on the RBD of S protein were characterized by a panel of 27 mAbs isolated from the immunized mice. Six groups of conformation-dependent epitopes, designated as Conf I-VI, and two adjacent linear epitopes were identified by ELISA and binding competition assays. The Conf IV and Conf V mAbs significantly blocked RBD-Fc binding to angiotensin-converting enzyme 2, suggesting that their epitopes overlap with the receptor-binding sites in the S protein. Most of the mAbs (23 of 25) that recognized the conformational epitopes possessed potent neutralizing activities against SARS pseudovirus with 50% neutralizing dose ranging from 0.005 to 6.569 microg/ml. Therefore, the RBD of SARS S protein contains multiple conformational epitopes capable of inducing potent neutralizing Ab responses, and is an important target site for developing vaccines and immunotherapeutics.
He
Yuxian
Y
Viral Immunology Laboratory, Lindsley F. Kimball Research Institute, New York Blood Center, New York, NY 10021, USA.
Lu
Hong
H
Siddiqui
Pamela
P
Zhou
Yusen
Y
Jiang
Shibo
S
D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal; D000914:Antibodies, Viral / Q000096:biosynthesis; D000956:Antigens, Viral / Q000737:chemistry* / Q000235:genetics; D001665:Binding Sites; D002460:Cell Line; D002522:Chlorocebus aethiops; D000939:Epitopes / Q000737:chemistry / Q000235:genetics; D006801:Humans; D066298:In Vitro Techniques; D008562:Membrane Glycoproteins / Q000737:chemistry* / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D009500:Neutralization Tests; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000276:immunology; D011487:Protein Conformation; D011991:Receptors, Virus / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000276:immunology; D045473:Severe acute respiratory syndrome-related coronavirus / Q000235:genetics / Q000276:immunology* / Q000472:pathogenicity; D064370:Spike Glycoprotein, Coronavirus; D014709:Vero Cells; D014759:Viral Envelope Proteins / Q000737:chemistry* / Q000235:genetics / Q000276:immunology* / Q000378:metabolism
D000911:Antibodies, Monoclonal; D000914:Antibodies, Viral; D000956:Antigens, Viral; D000939:Epitopes; D008562:Membrane Glycoproteins; D010446:Peptide Fragments; D011991:Receptors, Virus; D011993:Recombinant Fusion Proteins; D064370:Spike Glycoprotein, Coronavirus; D014759:Viral Envelope Proteins; C578557:spike glycoprotein, SARS-CoV; C578553:spike protein, mouse hepatitis virus