The enzyme DFPase from the squid Loligo vulgaris, is able to rapidlyand efficiently detoxify chemical warfare agents such as Sarin, whichwas used in the Tokyo subway attacks in 1995. A detailed understandingof the mechanism by which enzymes catalyze chemical reactions isnecessary for efforts aiming to improve their properties. A group ofresearchers at the University of Frankfurt, the Bundeswehr Institutefor Pharmacology and Toxicology in Munich, and Los Alamos NationalLaboratory in New Mexico, USA, have successfully determined thestructure of DFPase using neutron diffraction. They report theirfindings in the 20 January 2009 issue of the journal Proceedings ofthe National Academy of Sciences (106(3), 713-718).
The team used the neutron source at Los Alamos National Laboratory,one of only three sources worldwide equipped for proteincrystallography. In contrast to structure determination using X-rays,neutrons are able to locate the positions of hydrogen atoms, whichmake up half of all atoms in proteins, and are crucial for chemicalreactions. As X-rays interact with the electron cloud around an atomicnucleus, so heavier elements are more easily seen, while neutronsinteract with the atomic nuclei, and atoms in proteins such ashydrogen, oxygen, nitrogen, carbon, and sulfur, all scatter neutronsin a similar manner. Yet despite being so widespread, hydrogen atomsin proteins are quite elusive. As X-rays interact with the electroncloud around an atomic nucleus, hydrogen atoms, with only oneelectron, are normally invisible in structures. In contrast, neutronsinteract with the atomic nuclei, such that atoms in proteins,hydrogen, oxygen, nitrogen, carbon, and sulfur, all scatter neutronsin a similar manner. The two techniques therefore yield complementaryinformation about a protein structure. This information about hydrogenatoms is therefore essential for a basic understanding of the reactionmechanism of DFPase.
Neutron structures of proteins are quite rare and technicallydemanding, requiring large crystals and long measurement times. Thoughthe first neutron structure of a protein was reported 40 years ago, in1969, to date only about 20 unique structures have been solved, out of50000 entries in the Protein Data Bank. " The effort has beenabsolutely worth it, " says Junior-Prof. Julian Chen, who publishedthis work together with Dr. Marc-Michael Blum and Prof. HeinzRueterjans. " Based on the results of this study, we can now createtargeted changes to DFPase to augment the activity, as well asdiversify the substrate range of the enzyme."
Source: Goethe University Frankfurt