Sandbox I3DC 013

Structures of M. tuberculosis Rv2173 isoprenyl diphosphate synthase in substrate-bound forms James A. Titterington, Ngoc Anh Thu Ho, Charles P.H. Beasley, Francis Mann, Edward N. Baker, Timothy M. Allison, Jodie M. Johnston Molecular Tour Rv2173 is an Isoprenyl diphosphate synthase (prenyltransferase) from the human pathogen Mycobacterium tuberculosis. Prenyltransferases are important enzymes whose products act as components in the synthesis of a wide variety of natural products such as steroids, chlorophyll, carotenoids, and vitamin K2 (menaquinone). These enzymes act to produce long terpene polymers by sequentially adding IPP (isoprenyl diphosphate) monomers to an allylic substrate such as DMAP (dimethylallyldiphosphate). Rv2173 is folded as a decorated eight-helix bundle (Figure 1B), typical of the all-α-helical class I diterpene synthase fold. The belongs to are known as the all-E-prenyltransferase due to the stereochemistry of their product. This family produce a diverse array of products with the unique size and shape of each member enzymes active site pocket influencing the size (carbon length) of product they can make. Understanding the size of the product they produce helps to more clearly define their function within a cell. The cellular function of Rv2173 is a bit unclear, though recent work has suggested it may make shorter chain products (C10-C15 in length) and be involved in isoprenoid production for the synthesis of glycosyl carrier lipids. Analysis of the structures of Rv2173 managed to confirm it was a with a fold consistent with other all-E-prenyltransferases and gave important insights into the size of the active site pocket that controls product length. This analysis supports the suggestion that Rv2173 produces short chain products as the pocket size is limited by a range of bulky amino acid residues. Structures in the absence and presence of substrate were able to be compared revealing more open and closed forms of the enzyme. This can be seen, e.g., in comparison of DMAPP and IPP-bound structures: This gave insight into how the enzyme may close or open its active site by structural movements in order to protect its substrates during reaction and release product. References

spinqualitylabelsall models Rv2173 monomer (IPP-bound structure) with the core eight-helix bundle coloured blue, with the additional helices yellow. Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image