(color online) The 3D reconstructions of IgG antibody particles and nascent HDLs by OpNS and IPET. (a) A tilt series of a single-instance IgG antibody by OpNS ET displayed in the left-most column. The IPET method obtains the 3D model of an individual protein via an iterative refinement processes. The final 3D reconstruction of an individual antibody particle shows as purple in the top right. (a) and (b) A good fit obtained by fitting each domain of the crystal structure (PDB) into each density model of IgG in left bottom. (b) IPET to study the 3D conformation changes of their antibodies before and after peptide conjugation. (c) and (d) For more than 40 years, nobody knew the 3D structures of nascent HDLs, by using IPET, Zhang et al. revealed the typical structures of two 17 nm HDLs. Adapted from Ref. [48].