The present invention is directed to an isolated polypeptide containing SEQ ID NO: 1 or an immunogenic fragment thereof. Also disclosed is an isolated nucleic acid encoding the polypeptide or containing a sequence at least 70% identical to SEQ ID NO: 3. Within the scope of this invention are related expression vectors, host cells, and antibodies. Also disclosed are methods of producing the polypeptide, diagnosing coronavirus infection, and identifying a test compound for treating coronavirus infection.