 Hydrophobic amino acids are located between the β-sheets in the barrel and the surrounding α-helices to contribute to packing, such as the area containing Leu-168, Phe-170, Phe-189, Gly-311, and Phe-315.In the crystal, human transaldolase forms a dimer, with the two subunits connected by 18 residues in each subunit.See mechanism to the left for details.