Probing metal-ion-assisted π−π interaction in self-processing module of FrpC protein

Ladislav Bumba1, Petra Matyska Liskova1,2, Radovan Fiser1,2, Pavel Macek1, Jan Sýkora3,  Ivo Konopásek2

1Laboratory of Molecular Biology of Bacterial Pathogens, Institute of Microbiology, Czech Academy of Sciences, Videnska 1083, 14200 Prague 4, Czech Republic.

2Department of Genetics and Microbiology, Faculty of Science, Charles University in Prague, Vinicna 5, 12843 Prague 2, Czech Republic

3J. Heyrovsky Institute of Physical Chemistry,  Czech Academy of Sciences, Dolejškova 3, 18223 Prague 8, Czech Republic.


In the present work we describe a simple experimental model protein tailored to study the formation of metal ion-assisted π−π interaction during ligand-induced protein folding. The model system is based on a calcium-binding protein, SPM, a self-processing module, derived from the internal segment of the bacterial FrpC protein, which mediates a Ca2+-dependent autocatalytic cleavage of the highly specific Asp-Pro peptide bond and covalent linkage of the carboxy-terminal group of the splinter segment to ε-amino group of a lysine residue of an adjacent protein. SPM is a polypeptide that is intrinsically disordered in the absence of calcium and folds upon binding of Ca2+ ions into a compact and stable structure. The cleavage of the Asp-Pro bond is accompanied with the Ca2+-dependent folding of SPM that is unambiguously characterized by the formation of Ca2+-assisted π−π interaction between a pair of unique tryptophan residues. Therefore, Ca2+-dependent folding linked to enzymatic activity would prove SPM to be an excellent model to investigate the formation of Ca2+ππ interaction during the ligand-induced transition from an unfolded to the folded conformation.