Molecular Weight
Search the PDB by the combined molecular weight of all chains and ligands in the asymmetric unit. The molecular weight (in Daltons) of each component and the number of times it appears in the structure is found in the _entity category of the mmCIF file.
For example, 4HHB contains two chains A, two chains B, two PO4 ligands, and four HEM ligands for a molecular weight of 2*15150.5 + 2*15890.4 + 2*94.97 + 4*616.49 = 64737.7