FIG. 5.

Proposed model for the early interaction of Py with host cells. First, Py interacts with SA-containing cell receptors (step 1). This initial interaction is a prerequisite for subsequent proper recognition of the α4β1 integrin (step 2), either to promote a conformational change of the Py capsid, rendering the LDV motif more accessible to the integrin molecule, or to bring it in closer proximity to the integrin. This second interaction may facilitate the entry of the virus into the cells (step 3). Considering that both α4 and β1 integrin subunits are heavily glycosylated, carrying, in particular, terminal SA residues, integrins may themselves be a component of the SA-containing receptor molecules for Py (steps 1a and 2a) (see text).