Poster Presentation The 47th Lorne Conference on Protein Structure and Function 2022

Crystal structure of a complex between the electron-transfer partners arsenite oxidase and cytochrome c552, from the arsenite respiring bacterium Pseudorhizobium banfieldii str. NT-26. (#175)

Nilakhi Poddar 1 , Megan Maher 1 2 , Joanne Santini 3
  1. School of Chemistry, Bio21 Institute, University of Melbourne, Melbourne, VIC, Australia
  2. Department of Biochemistry and Genetics,, La Trobe Institute for Molecular Science, La Trobe University,, Melbourne, Victoria, Australia
  3. Institute of Structural and Molecular Biology, Division of Biosciences, University College London, London, United Kingdom

Arsenic, a toxic metalloid poses a great threat to human health by contaminating ground water systems [1]. Inorganic forms of arsenic i.e. arsenite (AsO33-) and arsenate (AsO43-), are toxic species. Interestingly, some prokaryotes have developed unique mechanisms that utilise arsenite and arsenate for respiration and therefore as energy sources.

The organism Pseudorhizobium banfieldii str. NT-26, respires with arsenite and employs the arsenite oxidase (Aio) for its crucial respiratory activity. Aio consists of a large catalytic subunit (AioA), which contains a MGD center and a 3Fe-4S cluster, and a small subunit (AioB) containing a Rieske 2Fe-2S cluster. Arsenite is oxidized to arsenate at the Mo site, concomitantly reducing Mo(VI) to Mo(IV) [2]. The electrons are then passed to the 3Fe-4S cluster, the 2Fe-2S cluster in AioB and finally to an electron acceptor: cytochrome c552 (cyt c552) [2, 3]. To date, the structure of the Aio and cyt c552 complex has not been investigated, and the kinetics and thermodynamics of the Aio to cyt c552 interaction are unknown.  In this study, we describe the structure of the Aio/cyt c552 complex, determined by X-ray crystallography. Structural analysis of the interface shows that the Aio enzyme docks within a pocket adjacent to the cyt c552 active site, owing to a close contact of ~ 9.0 Å between the cyt c552 heme cofactor and the 2Fe-2S cluster in AioB subunit; it also shows how various types of interactions (hydrogen bonding, salt bridges and electrostatic interactions) helps to determine the rate of electron transfer between the complex.

References:

[1]         H. V. Aposhian, and M. M. Aposhian, “Arsenic toxicology: five questions,” Chem Res Toxicol, vol. 19, no. 1, pp. 1-15, Jan, 2006.

[2]         T. P. Warelow, M. Oke, B. Schoepp-Cothenet, J. U. Dahl, N. Bruselat, G. N. Sivalingam, S. Leimkühler, K. Thalassinos, U. Kappler, and J. H. Naismith, “The respiratory arsenite oxidase: structure and the role of residues surrounding the rieske cluster,” PLoS One, vol. 8, no. 8, pp. e72535, 2013.

[3]         P. J. Ellis, T. Conrads, R. Hille, and P. Kuhn, “Crystal structure of the 100 kDa arsenite oxidase from Alcaligenes faecalis in two crystal forms at 1.64 Å and 2.03 Å,” Structure, vol. 9, no. 2, pp. 125-132, 2001.