Structural Study of X-Ray Induced Activation of Carbonic Anhydrase.Sjoblom, B., Polentarutti, M., Djinovic-Carugo, K.
(2009) Proc Natl Acad Sci U S A 106: 10609
- PubMed: 19520834
- DOI: https://doi.org/10.1073/pnas.0904184106
- Primary Citation of Related Structures:
- PubMed Abstract:
Carbonic anhydrase, a zinc metalloenzyme, catalyzes the reversible hydration of carbon dioxide to bicarbonate. It is involved in processes connected with acid-base homeostasis, respiration, and photosynthesis. More than 100 distinct human carbonic anhydrase II (HCAII) 3D structures have been generated in last 3 decades [Liljas A, et al. (1972) Nat New Biol 235:131-137], but a structure of an HCAII in complex with CO(2) or HCO(3)(-) has remained elusive. Here, we report previously undescribed structures of HCAII:CO(2) and HCAII:HCO(3)(-) complexes, together with a 3D molecular film of the enzymatic reaction observed successively in the same crystal after extended exposure to X-ray. We demonstrate that the unexpected enzyme activation was caused in an X-ray dose-dependent manner. Although X-ray damage to macromolecular samples has long been recognized [Ravelli RB, Garman EF (2006) Curr Opin Struct Biol 16:624-629], the detailed structural analysis reports on X-ray-driven reactions have been very rare in literature to date. Here, we report on enzyme activation and the associated chemical reaction in a crystal at 100 K. We propose mechanisms based on water photoradiolysis and/or electron radiolysis as the main cause of enzyme activation.
Department for Structural and Computational Biology, Max F Perutz Laboratories, University of Vienna, Campus Vienna Biocenter 5, A-1030 Vienna, Austria.