Proposed membrane organization of syb and syx for the BAT models. (A) The pre-docking state of a synaptic vesicle (lavender) is shown prior to contact with the plasma membrane (pink). The intra-membrane, hydrophobic domains of vesicle-associated syb and plasma membrane-associated syx (in dark blue with the single letter code denoting the amino acid sequences of the mouse proteins here and in all later panels) are shown at the interface between the inner and outer hemi-bilayers. These intra-membrane sequences are proposed to adopt β-structure which is preserved in panels (B-E). Palmitoylation of C (cysteine) residues is not depicted. The C-ends of syb and syx are presumably modified to eliminate their charge (B) Once SNARE zippering commences and the synaptic vesicle contacts the plasma membrane, it initiates a translocation of the hydrophobic domains of syb and syx from the inter-leaflet position shown here toward the vesicle-plasma membrane interface as illustrated in C (C) This shows an intermediate state in which the hydrophobic domains of syb and syx are re-locating to the vesicle-plasma membrane interface (D) This is a cross-sectional representation of the docked and primed state of the synaptic vesicle-plasma membrane interface for the BAT model. Syb sequence is dark blue while syx is green. The syx partner for syb would sit behind the plane of this image, as would the syb partner for syx (E) "Top" view of the organization of syb-syx pairs of a docked and primed synaptic vesicle. This is the postulated end-to-end organization of the syb-syx pairs that one would observe by removing the external leaflet of the plasma membrane thereby exposing the elongated β-structure of these domains. Note that these images are drawn to accentuate the arrangement of syb and syx, first within their respective membranes and then at the interface between the vesicle and plasmalemma.