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. 2015 Mar 31;6:66. doi: 10.3389/fphar.2015.00066

FIGURE 5.

FIGURE 5

Variety of fusion partners used for crystallization of GPCRs. A flexible T4L molecule consists of an N-terminal (cyan) and a C-terminal lobe (blue) connected via a helix C (pink); helix A (green) precedes the N-terminal lobe (A–D). Disulfide bonds (yellow spheres) decrease molecular flexibility in dsT4L (C). On the other hand, molecular size of T4L was reduced by deleting the N-terminal lobe in mT4L (D). The insertion sites of the fusion partners into ICL 3 are exactly the same for all three M3 receptor constructs (B–D). Both T4L and BRIL (red) were used as N-terminal fusion partners (A,E). Structures of the BRIL chimeras show clearly the sodium-ion allosteric site (E,F). In the Rd (orange) chimera, a Zn2+ ion substitutes the naturally occurring Fe2+/3+ (G). PGS (green) was identified as a fusion partner most recently (H). For all structures, C atoms of the orthosteric ligands are represented as orange spheres. PDB IDs: 4GBR (A), 4DAJ (B), 4U14 (C), 4U15 (D), 4N6H (E), 4EIY (F), 4MBS (G) and 4RNB (H).