Natively Inhibited Trypanosoma brucei Cathepsin B Structure Determined by Using an X-ray Laser

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Science  11 Jan 2013:
Vol. 339, Issue 6116, pp. 227-230
DOI: 10.1126/science.1229663

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Diffraction Before Destruction

A bottleneck in x-ray crystallography is the growth of well-ordered crystals large enough to obtain high-resolution diffraction data within an exposure that limits radiation damage. Serial femtosecond crystallography promises to overcome these constraints by using short intense pulses that out-run radiation damage. A stream of crystals is flowed across the free-electron beam and for each pulse, diffraction data is recorded from a single crystal before it is destroyed. Redecke et al. (p. 227, published online 29 November; see the Perspective by Helliwell) used this technique to determine the structure of an enzyme from Trypanosoma brucei, the parasite that causes sleeping sickness, from micron-sized crystals grown within insect cells. The structure shows how this enzyme, which is involved in degradation of host proteins, is natively inhibited prior to activation, which could help in the development of parasite-specific inhibitors.


The Trypanosoma brucei cysteine protease cathepsin B (TbCatB), which is involved in host protein degradation, is a promising target to develop new treatments against sleeping sickness, a fatal disease caused by this protozoan parasite. The structure of the mature, active form of TbCatB has so far not provided sufficient information for the design of a safe and specific drug against T. brucei. By combining two recent innovations, in vivo crystallization and serial femtosecond crystallography, we obtained the room-temperature 2.1 angstrom resolution structure of the fully glycosylated precursor complex of TbCatB. The structure reveals the mechanism of native TbCatB inhibition and demonstrates that new biomolecular information can be obtained by the “diffraction-before-destruction” approach of x-ray free-electron lasers from hundreds of thousands of individual microcrystals.

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