Protein Complexes


Inside cells, individual gene products often function in concert with other gene products, forming complexes. Usually these are protein-only complexes, but they can contain RNA as well. The associations responsible for complex formation can be strong or weak making stable or transient complexes, respectively. Any two proteins within a complex need not interact directly with each other as they might be linked together by a different protein or RNA. Chaperone-target, protease-target, and translocon-substrate interactions are numerous and can complicate the interpretation of complexes, as can the presence of minor non-stoichiometric "subunits" in general. Abundant or sticky proteins, e.g ribosomal proteins may non-specifically contaminate in vivo complexes during isolation. Some subunits may remain after playing a role in assembly or have very subtle roles. Very small subunits may escape detection.

Proteins commonly work in aggregate, e.g. the replisome, RNA polymerases, the ribosome, the flagellar apparatus, the RNA degradosome, the Clp proteosome, the translocon. These and other complexes are well studied and subcomplexes detected by proteomics studies may be grouped into topics with them.

Many proteins function as homo-oligomers, such as the tendency of many repressors to form dimers. Proteins can adopt more than one alternate homo-oligomeric state, such as proteins that tend to form fibrils. Homogenous subunits can utilize homo-oligomerization domain surfaces for sub-assembly before going into heterogenous complexes.


A wide variety of approaches have been undertaken to predict and experimental identifiy protein complexes.
The results of two large Blue Native 2D gel studies are presented as Experimental subTopics.

GenePages of proteins that form heterogenous oligomers are linked to TopicPages clustering the interacting proteins. SuperTopics of these complex-oriented TopicPages describe the high-throughput experimens that identified the complexes.
Additional detailed studies supporting individual complexes may be cited in the TopicPage bibliographies.