Introduction

It was realized, long ago, that a folded protein “consists of one polypeptide chain which continues without interruptions throughout the molecule (or, in certain cases, of two or more such chains)” and that “this chain is folded into a uniquely defined configuration, in which it is held by hydrogen bonds” [1]. Later on, a series of other non-covalent interactions have been discovered to be responsible for protein folding, stability, plasticity, and function, like van der Waals, hydrophobic and electrostatic interactions [2]. One of these non-covalent interactions has received little attention insofar: it is the chalcogen bond.
It is an attractive interaction between chalcogen atoms (sulfur, selenium or tellurium) and nucleophiles. In molecular moieties like R-X-R (X = S, Se or Te), the nucleophile tends to occupy a position along the extension of one of the R-X covalent bonds (Figure 1 )[3]. Although recent publications reviewed extensively both theoretical and experimental studies of chalcogen bonds [4][5], minor attention has been paid to this non-covalent interaction in biological systems.