Table 1.

Major proteins of coronavirus and their functions.

Major protein	Function
Nucleocapsid protein (N)	Multifunctional protein
	Forms complexes with genome RNA to make up nucleocapsid
	Interacts with the membrane proteins during virus life cycle, especially for virion assembly and viral budding
	Enhances the efficiency of virus transcription
	Principle target for vaccine development as a major immunogen (13)
	An important diagnostic marker for coronavirus disease (13, 14)
Spike or peplomer protein (S)	Critical for binding to host cell receptors to facilitate entry into host cell (15)
Envelope protein (E)	Smallest of the major proteins
	Interacts with M protein to form viral envelop
	Expressed abundantly inside the infected cell but only a small portion incorporated into virion envelope (16)
	A majority is localized at the site of intracellular trafficking, i.e., the ER, Golgi, and ER–Golgi intermediate compartment where it participates in virus assembly and budding (17)
Membrane protein (M)	Most abundant structural protein
	Central organizer of CoV assembly (18, 19)
	Defines shape of viral envelope
	Responsible for transmembrane transport of nutrients and bud release
Hemagglutinin-esterase glycoprotein	Mediate reversible attachment to sialic acids
	Act both as carbohydrate-binding lectin and as a receptor-destroying enzyme (RDE) (20)
	Responsible for enzymatic activity
	Lack membrane fusion activity
	Accessory to spike glycoprotein in virion (21)