Acta Crystallographica Section D

Biological Crystallography

Volume 69, Part 10 (October 2013)

research papers

Acta Cryst. (2013). D69, 2072-2080    [ doi:10.1107/S0907444913019276 ]

Determination of the GH3.12 protein conformation through HPLC-integrated SAXS measurements combined with X-ray crystallography

A. Round, E. Brown, R. Marcellin, U. Kapp, C. S. Westfall, J. M. Jez and C. Zubieta

Abstract: The combination of protein crystallography and small-angle X-ray scattering (SAXS) provides a powerful method to investigate changes in protein conformation. These complementary structural techniques were used to probe the solution structure of the apo and the ligand-bound forms of the Arabidopsis thaliana acyl acid-amido synthetase GH3.12. This enzyme is part of the extensive GH3 family and plays a critical role in the regulation of plant hormones through the formation of amino-acid-conjugated hormone products via an ATP-dependent reaction mechanism. The enzyme adopts two distinct C-terminal domain orientations with `open' and `closed' active sites. Previous studies suggested that ATP only binds in the open orientation. Here, the X-ray crystal structure of GH3.12 is presented in the closed conformation in complex with the nonhydrolysable ATP analogue AMPCPP and the substrate salicylate. Using on-line HPLC purification combined with SAXS measurements, the most likely apo and ATP-bound protein conformations in solution were determined. These studies demonstrate that the C-terminal domain is flexible in the apo form and favours the closed conformation upon ATP binding. In addition, these data illustrate the efficacy of on-line HPLC purification integrated into the SAXS sample-handling environment to reliably monitor small changes in protein conformation through the collection of aggregate-free and highly redundant data.

PDB reference: 4l39

Keywords: small-angle X-ray scattering; GH3 family; acyl acid-amido synthetase; hormone amino-acid conjugates.

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