Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

Proteins are important biomolecules in all living cells. They perform a large array of functions within organisms. To understand the speciation of actinides in living organisms, their interactions with proteins need to be explored on a molecular level.
Bacterial surface layers (S-layers) are common surface structures in many bacteria and archaea consisting of so-called surface-layer proteins (S-layer proteins) [1]. So far, we could show that S-layers proteins of Lysinibacillus sphaericus JG-A12 selectively bind several metals including U, Pd, Au, and Eu, partly with a high affinity [2]. In the present work we studied the interaction of Cm(III) with bacterial S-layer proteins of L. sphaericus JG-A12.
The formation of aqueous Cm(III) S-layer protein complexes was studied at room temperature by time-resolved laser-induced fluorescence spectroscopy (TRLFS) in 0.1 M NaCl solutions. The experiments were performed at a fixed total concentration for Cm(III) 0.88 µM and the S-layer protein of 5 g/L (39.6 µM) by varying the pH (2.0-9.0) and the type of S-layer. Based on their individual luminescence spectra and lifetimes, a specific and unspecific Cm(III) binding could be distinguished. The formation of the specific Cm3+-S-layer complex A and unspecific Cm3+-S-layer complex B depend on pH and the Ca2+ amount in the S-layer types. The influence of Ca2+ on the Cm3+ S-layer complexation was investigated by Ca2+ titration experiments. The specific Cm3+-S-layer complex A is characterized by a narrow emission band at 602.5 nm combined with a long lifetime of 310 µs. The spectroscopic EDTA titration of Cm3+-S-layer complex A showed an exchange of S-layer ligands by EDTA in the first coordination sphere of Cm(III) at EDTA concentrations of 40 µM and higher. This corresponds to a EDTA:S-layer protein ratio of 1:1.

References:

[1] M. Sára, U.B. Sleytr, J. Bacteriol. 2000, 182,859. [2] M.L. Merroun et al., Appl. Environ. Microbiol. 2005, 71,5532.