The disclosure pertains to the field of molecular means capable of binding calcium, in particular peptides which are calcium chelators, appropriate for use in vitro or in vivo and preferably capable of targeting specific cellular compartments. Polypeptide comprising a first calcium-binding domain, a peptide linker and a second calcium binding domain, wherein the first and second binding domains are linked through the peptide linker, and wherein: the first calcium-binding domain and the second calcium binding domain each comprise at least one calcium-binding site derived from a EF-hand motif; and, the first calcium-binding domain and the second calcium binding domain differ in at least one calcium-binding site.