Influence of divalent cations in the protein crystallization process assisted by lanthanide-based additives
Résumé
Lanthanide complexes are now widely used as powerful auxiliaries for protein crystallisation to improve the crucial nucleation and phasing steps. We systematically analysed the influence of the commercial crystallisation kit composition on the efficiency of two lanthanide additives [Na]$_3$[Eu(DPA)$_3$] and Tb-Xo4, we developed. This study revealed that our initial the trisdipicolinate complex presents a lower chemical stability and a strong tendency to self-crystallisation detrimental for its use in highthroughput robotised crystallisation platform. In particular, we reported herein the crystal structures of (Mg(H$_2$O)$_6$)$_3$ [Eu(DPA)$_3$]$_2$•7H$_2$O (1),{(Ca(H$_2$O)$_4$)$_3$[Eu(DPA)$_3$]$_2$}$_n$•11nH$_2$O (2) and {Cu(DPA)(H$_2$O)$_2$}$_n$ (3) resulting from spontaneous crystallisation in the presence of divalent alkaline earth cation or transmetallation. On the other hand, the Tb-Xo4 is perfectly soluble in the crystallisation media, stable in the presence of alkaline-earth dications and slowly decomposed (within days) by trans-metalation with transition metals. The original structure of [Tb$_4$L$_4$(H$_2$O)$_4$]Cl$_4$•15H$_2$O (4) is also described. In this article, we also discussed the potential beneficial interactions between the crystallisation mixture components and Tb-Xo4 leading to the formation of more complex adducts observed in the case of the AdKA protein crystallisation, like {AdkA/Tb-Xo4/Mg$^{2+}$ /glycerol} in the protein binding sites. The observation of such multi-components adducts illustrates the complexity and the versatility of the supramolecular chemistry occurring at the surface of proteins.
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