This invention relates to protein fiber formation and in particular to methods of producing protein fibers to form a protein structure comprising a plurality of first polypeptide units arranged in a first polypeptide strand and a plurality of second polypeptide units arranged in a second polypeptide strand, the strands preferably forming a coiled coil structure, and in which a first polypeptide unit in the first strand extends beyond a corresponding second polypeptide unit in the second strand in the direction of the strands.