 | Acta Crystallographica Section F Acta Crystallographica Section F STRUCTURAL BIOLOGY COMMUNICATIONS |
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![[Figure 2]](ji5030fig2mag.jpg)
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Figure 2
X-ray crystallographic analysis of Colchicalin in the apo form compared with its complex with colchicine. (a) Superposition of Colchicalin D6.2 in the apo state (loops in cyan) with Colchicalin Δ4-D6.3 in complex with colchicine (PDB entry 5nkn; loops in violet). (b) Binding mechanism for colchicine. In the apo state the side chains of Ile97 in loop #3 and of Phe71 in loop #2 point into the ligand pocket (cyan). In the complex, the drastic rearrangement of loop #3 in combination with the (upward/outward) side-chain flip of Phe71 enables the tight fit of colchicine within the ligand pocket. Of note, the cis-peptide bond between Phe71 and Pro72 in loop #2 is present in both structures. (c) Side-chain conformations of Met69 in the apo structure in comparison with Gln69 in the structure of the ligand complex. The carboxamide group of glutamine forms an additional hydrogen bond to the main-chain O atom of Ala52 (red dashed line). (d) A concerted change in side-chain conformations upon colchicine binding. In the complex, the side chains of Met51 at the C-terminal end of loop #1 and Met73 in loop #2 (violet) are directed towards the bound colchicine, whereas in the apo state they point away from the binding site. It seems that the inward movement of the Phe71 side chain in the apoprotein drags along the neighboring residue Met73 in loop #2, whose bulky side chain laterally pushes aside that of Met51 in loop #1. |
![[Figure 2]](ji5030fig2.jpg)
| STRUCTURAL BIOLOGY COMMUNICATIONS |
ISSN: 2053-230X
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