|MoBio||Three-Dimensional Structure||Chapter 2|
The three-dimensional (3D) structure is also called the tertiary structure. If a protein molecule consists of more than one polypeptide, it also has the quaternary structure, which specifies the relative positions among the polypeptides (subunits) in a protein.
X-ray crystallography and nuclear magnetic resonance (NMR) are the major experimental techniques for determining the 3D structures of macromolecules. Protein Data Bank is the most important site for structural information which can easily be accessed by the "PDB ID" of a macromolecule.