Fig. 3. The Stochastic Velcro model of rhodopsin enrichment in disc membranes.

Rhodopsin density in the disc membranes is twice that in the plasma membrane, indicating that it is not efficiently separated into disc membranes. One possible explanation for this asymmetry is that rhodopsin self-associates at is extracellular N-termini. This may result in a Velcro-like coupling of the nascent disc membranes and producing a self-binding sink driving disc enrichment. Affinity would not be expected to be high for this interaction since it only produces a twofold difference in disc vs plasma membrane density. This interaction may also help drive disc morphogenesis. For simplicity, rhodopsin cis dimers (in the same membrane) are not depicted in this schematic.