Racemic protein crystallography utilizes synthetic protein enantiomers for crystallization and is a technology particularly useful at yielding atomistic structural insights. Unlike native Lproteins, racemic proteins can crystallize into achiral space groups possessing higher symmetry and order (Figure ). Solving structure based on racemic proteins can be advantageous. As illustrated in the first example, the phase issue in solving the structure of rubredoxin was vastly simplified, because the space group was found to be centrosymmetric with the crystal unit cell containing a center of inversion (Figure ). The off-diagonal phases of the X-ray diffraction data obtained from a centrosymmetric crystal cancel out, restricting the phases to 0° or 180°, as opposed to the possible 0° to 360° arising from a homochiral crystal. Additionally, the centrosymmetric crystal has high dimensionality. This generally results in rapid protein crystallization and structure solving with high-resolution detail, in addition to unveiling solute and ligand interactions. Considering the higher order of crystal symmetry and favorable crystal growth, racemic protein crystallography has been used to resolve X-ray structures of numerous proteins up to ultra-high (sub-angstrom) resolution (Table ). Indeed, 12 (20% so far) of the reported racemic crystal structures were resolved in the centrosymmetric space group P-1. Many quasi-racemic crystal structures, in which the enantiomers differ slightly, are reported to adopt the space group P1 due to a lack of true symmetry. However, it is more appropriate to classify these crystals as pseudo-centrosymmetric or "pseudo-P-1." Almost half of the racemic structures were resolved in centrosymmetric/pseudocentrosymmetric space groups, the other half were also resolved in chiral space groups (Table ). Notably, there are no reported instances of a single enantiomer crystallizing into a chiral space group from a racemate. Thus, crystallization of proteins from racemates may have advantages beyond that explained by the achiral space group theory (for review -see ref ). Racemic protein crystallography has been most frequently applied to study miniproteins containing fewer than 100 residues. These proteins are known to be difficult to crystallize because of their globular morphology which unfavors crystal packing. Meanwhile, their small sizes render the chemical synthesis of these proteins feasible (see Section 3 below for synthetic approaches). Some of the unique insights generated by racemic crystallography are listed below: