Protein Complex Assembly

Most proteins do not function as fully extended polypeptide chains but assemble into compact multicomponent complexes. During assembly, the growing complex must distinguish its specific components from a mixture of hundreds of different protein and non-protein species present in the cell. 

Protein complexes can be either homomeric, consisting of several copies of the same polypeptide chain, or heteromeric, composed of multiple distinct polypeptide chains or non-protein components.

Usually, proteins have all the necessary information to self-assemble into functional complexes from their constituents with speed and precision. 

Many viruses can self-assemble to form a fully functional unit using the infected host cell to produce all of the necessary components.

For instance, in the tobacco mosaic virus, coat protein subunits self-assemble into individual rings, in vitro. An RNA molecule binds in the center of the growing helix to make the active virus.  

However, in some protein complexes, self-assembly is only due to mutation or disease. 

Hemoglobin, the oxygen-carrying protein found in red blood cells, is a tetramer of two alpha subunits and two similar beta subunits. However, in si