Protein lattices are disclosed which have a regular structure with a repeating unit repeating in three dimensions and have many uses, for example to support an array of macromolecular entities for X-ray crystallography. The repeating unit comprises protein protomers which each comprise at least two monomers fused together. The monomers are each monomers of a respective oligomer assembly into which the monomers are assembled for assembly of the protomers into the lattice. The repeating unit comprises protomers comprising at least a first monomer which is a monomer of a first oligomer assembly which has a set of rotational symmetry axes extending in three dimensions, and a further monomer fused to the first monomer which further monomer is a monomer of a further oligomer assembly which has a rotational symmetry axis of the same order as one of the set of rotational symmetry axes of the first oligomer assembly.