Composite polypeptide having a metal binding motif and molecular construct comprising the same

A linker unit, comprising,

• a center core, wherein the center core comprises,
• 2 to 10 lysine (K) residues,
• optionally, one or more fillers, wherein any two of the K residues are adjacent to each other or are separated by the filler,
• optionally, a terminal spacer, wherein the terminal spacers is an N-terminal spacer linked to the N-terminus of the first K residue or a C-terminal spacer linked to the C-terminus of the last K residue, and each of the filler and the terminal spacer comprises, independently, (1) 1 to 12 non-K amino acid residues, or (2) a PEGylated amino acid having 1 to 12 repeats of ethylene glycol (EG) unit, and
• a SH-reactive group, linked to the first or last K residue of the center core by forming an amide bond therewith, or when the terminal spacer is present, the SH-reactive group is linked to the terminal amino acid residue of the terminal spacer by forming an amide bond therewith, wherein the center core carries a local negative charge at or near the amino acid residue linked with the SH-reactive group;
• and
• 2 to 10 targeting, effector or pharmacokinetic elements, wherein,
• each targeting, effector or pharmacokinetic element is linked to the K residue of the core, or
• when the molecular construct further comprises 2 to 10 linking arms, one terminus of each linking arm is linked to the K residue of the core via forming an amide bond with the ε-amino group of the K residue, and the other terminus of each linking arm is linked to each targeting, effector or pharmacokinetic element, wherein the linking arm is a peptide comprising 2-12 non-K amino acid residues or a polyethylene glycol (PEG) chain having 2-24 repeats of EG units.