FIG. 7.

Model of 19-kDa GP₁ and locations of key receptor binding residues. (A) Ribbon diagram of 19-kDa GP₁ showing key recombinant RBRs used in this study, including RBR-7 (residues 90 to 149; dark blue), RBR-1 (residues 57 to 149; dark blue and green), and RBR-12 (residues 33 to 193; dark blue, green, and pink). The side chains of K95, K114, K115, and K140 are shown. Cysteines involved in disulfide bonds are shown in red. An asterisk (*) denotes a contact point between the β1 and β13 strands. (B) Surface rendering (top view) of the GP_1,2Δ trimer structure. One monomer is colored dark gray for clarity. (C and D) Model of GP_1,2Δ trimer after cleavage by cathepsins B and L, viewed from the top (C) and side (80° rotation) (D). Residues that decreased RBR-1-Fc binding when replaced with Ala are shown in all figures (K95, orange; K114, K115, and K140, cyan). The graphic representations were based on PDB file 3CSY (14) and rendered with Pymol. Note that the depictions in panels A, C, and D are only models that assume no conformational changes in GP₁ following proteolytic priming.