Chlorite dismutase

Photosynthesis is not the only dioxygen-evolving biological process. For instance, chlorite dismutase (Cld; EC 1.13.11.49) catalyses the production of O₂ from chlorite (1):

ClO2− → Cl− + O2

(1)

The reaction (1) is not really disproportionation, and NC-IUBMB made a valid point that the term “chlorite dismutase” is “misleading”. Even so, the NC-IUBMB-approved, sorry, “accepted” name “chlorite O₂-lyase” for an oxidoreductase is equally absurd; I am going to ignore it.

Chlorite dismutase from Azospira oryzae exists as a homohexamer [1] while Cld from Dechloromonas aromatica [2] and enzyme from Candidatus Nitrospira defluvii [3] are homopentamers.

The active site contains a single haem group [Fe(ppIX)] coordinated by a proximal histidine residue. Goblirsch et al. [2] propose the mechanism where the reaction of chlorite within the distal pocket of Cld generates hypochlorite (ClO⁻) and a compound I intermediate [Fe(ppIX)O] (1a). Then ClO⁻ rebounds with compound I forming the chloride and dioxygen (1b):

ClO2− + [Fe(ppIX)] → ClO− + [Fe(ppIX)O]	(1a)
ClO− + [Fe(ppIX)O] → Cl− + O2 + [Fe(ppIX)]	(1b)

1. de Geus, D.C., Thomassen, E.A.J., Hagedoorn, P.-L., Pannu, N.S., van Duijn, E. and Abrahams, J.P. (2009) Crystal structure of chlorite dismutase, a detoxifying enzyme producing molecular oxygen. J. Mol. Biol. 387, 192—206.
2. Goblirsch, B.R., Streit, B.R., DuBois, J.L. and Wilmot, C.W. (2010) Structural features promoting dioxygen production by Dechloromonas aromatica chlorite dismutase. J. Biol. Inorg. Chem. 15, 879—888.
3. Kostan, J., Sjöblom, B., Maixner, F., Mlynek, G., Furtmüller, P.G., Obinger, C., Wagner, M., Daims, H. and Djinović-Carugo, K. (2010) Structural and functional characterisation of the chlorite dismutase from the nitrite-oxidizing bacterium “Candidatus Nitrospira defluvii”: Identification of a catalytically important amino acid residue. J. Struct. Biol. 172, 331—342.

Femtosecond X-ray nanocrystallography of PSI

It is a well known fact (to those who know it well) that in order to obtain a decent diffraction pattern one has to grow a decent-size crystal first. Well, that is about to change. The PDB entry enigmatically named “femtosecond X-ray protein nanocrystallography” [1] in fact contains the structure of the photosystem I (PSI) from Thermosynechococcus elongatus solved by this new method [2]. In this work, more that 3 million diffraction patterns were collected from really small PSI crystals (from ~200  nm to 2  μm in size) illuminated by the new femtosecond X-ray laser, the Linac Coherent Light Source in Stanford. According to the authors,

We mitigate the problem of radiation damage in crystallography by using pulses briefer than the timescale of most damage processes.

1. PDB:3PCQ
2. Chapman, H.N., Fromme, P., Barty, A. et al. (2011) Femtosecond X-ray protein nanocrystallography. Nature 470, 73—77.

P450 from Actinoplanes teichomyceticus

The crystal structure of the P450 monooxygenase from Actinoplanes teichomyceticus (CYP165D3) involved in biosynthesis of antibiotic teicoplanin has been solved [1].

1. Li, Z., Rupasinghe, S., Schuler, M. and Nair, S.K. (2011) Crystal structure of a phenol-coupling P450 monooxygenase involved in teicoplanin biosynthesis. Proteins: Structure, Function, and Bioinformatics 79, 1728—1738.

P450 monooxygenase AurH from S. thioluteus

The first crystal structures of the unique P450 monooxygenase AurH from Streptomyces thioluteus have been solved [1].

1. Zocher, G., Richter, M.E.A., Mueller, U. and Hertweck, C. (2011) Structural fine-tuning of a multifunctional cytochrome P450 monooxygenase. J. Am. Chem. Soc. 133, 2292—2302.