Molecular organization of a recombinant subviral particle from tick-borne encephalitis

The tick-borne encephalitis (TBE) flavivirus contains two transmembrane pro teins, E and M. Coexpression of E and the M precursor (prM) leads to secret ion of recombinant subviral particles (RSPs). In the most common form of th ese RSPs, analyzed at a 19 Angstrom resolution by cryo-electron microscopy (cryo-EM), 60 copies of E pack as dimers in a T = 1 icosahedral surface lat tice (outer diameter, 315 Angstrom). Fitting the high-resolution structure of a soluble E fragment into the RSP density defines interaction sites betw een E dimers, positions M relative to E, and allows assignment of transmemb rane regions of E and M. Lateral interactions among the glycoproteins stabi lize this capsidless particle; similar interactions probably contribute to assembly of virions. The structure suggests a picture for trimer associatio n under fusion-inducing conditions.