Protein structures and protein fibres

A method of forming a protein structure comprising:

• mixing a plurality of copies of a first peptide monomer unit with a plurality of copies of a second peptide monomer unit, whereby the plurality of copies of the first peptide monomer unit and the plurality of copies of the second peptide monomer unit self-assemble to form a heterodimer comprising a first strand comprising the plurality of copies of the first peptide monomer unit and a second strand comprising the plurality of copies of the second peptide monomer unit, wherein each of the first and second monomer units comprise a heptad repeat motif (with positions in each of the motifs represented by abcdefg), wherein each of the heptad repeat motif has a pattern of hydrophobic (H) and polar (P) amino acid residues represented by HPPHPPP, wherein the sequence of the first strand and the sequence of the second strand are non-identical, and wherein said first and second monomer units together comprise a pair of amino acid residues selected from the group consisting of:
• a pair of asparagines, a pair of arginines, and a pair of lysines, wherein one amino acid residue of each pair is in an “a” position of a heptad repeat motif on each of the first and second peptide monomer units, and wherein at least one charged amino acid residue of the first peptide monomer unit is arranged to attract an oppositely-charged amino acid residue of the second peptide monomer unit, and wherein the pair of amino acid residues in the “a” positions are in motifs that are in different ordinal positions within the first and second peptide monomer units such that upon heterodimerization at least one motif on each strand overhangs the heterodimer, whereby the first strand and the second strand form a staggered, parallel, heterodimer, coiled-coil structure.