Enterovirus 71 / EV71 is a small non-enveloped virus that contains a positive-sense, single-stranded RNA molecule of approximately 7,400 nucleotides (nt) as its genome. In this RNA molecule, there is a 5'- and 3'- untranslated regions (UTRs) that participate in viral RNA replication; the central area is translated as a single polyprotein, which is then processed into three main cleavage intermediates P1, P2 and P3 by proteolysis. The intermediate P1 can be further cleaved into four structural proteins VP1, VP2, VP3, and VP4 of which the molecular weights are 33 kDa, 28 kDa, 27kDa and 8 kDa, respectively; the intermediate P2 are processed into three nonstructural proteins 2A, 2B and 2C; and the cleavage of intermediate P3 produces four nonstructural proteins 3A, 3B, 3C, and 3D.
Proteins VP1, VP2 and VP3 form a pentameric subunit, of which 60 copies are connected to form an icosahedral capsid; while VP4 are attached to the inner surface of the capsid. VP1 to 3 are also considered to have immunologically reactive epitopes, though identified neutralizing antibodies are mainly induced by VP1.
Additionally, the entry of enterovirus 71 / EV71 to human cells is mediated by the interaction of VP1 with its cellular receptors scavenger receptor B2 and P-selectin glycoprotein ligand-1. Functions of the non-structural proteins are listed as follows: 2A, viral protease, also participates in inhibiting host protein synthesis; 2B, plays an important role in increasing membrane permeability; 2C, acts as an inhibitors of cellular secretory pathways, and it also takes part in vesicle formation, NTPase; 3A, inhibits intracellular transport; 3B, also known as Vpg, primes RNA synthesis; 3C, viral protease, inhibits host transcription; and 3D, works as a viral polymerase.
Fig 2. EV71 genome structure
Fig 3. EV71 EV71-5' UTR.png
The first and the last nucleotides in each stem-loop and the position of the functional initiator AUGs are indicated. The body of the IRES within the 5' UTR is underlined.
Fig 4. EV71 capsid structure
A. Cartoon diagram of enterovirus 71 / EV71 icosahedral asymmetric unit showing VP1 (blue), VP2 (green), VP3 (red), and VP4 (yellow) calcium ions (magenta) and the pocket factor (orange). The positions of the prominent capsid surface features are indicated by dashed lines. B. Molecular surfaces of five icosahedral asymmetric units of enterovirus 71 / EV71 viewed down a fivefold axis.
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