A protein complex is a group of two or more proteins. Protein complexes are a form of quaternary structure. Proteins in a protein complex are linked by non-covalent protein-protein interactions, and different protein complexes have different degrees of stability over time. Protein complex formation often serves to activate or inhibit one or more of the complex members. In this way protein complex formation can be similar to phosphorylation. A method that is commonly used for identifying the members of protein complexes is immunoprecipitation.
Understanding the functional interactions of proteins is an important research focus in biochemistry and cell biology. Protein complex formation often serves to activate or inhibit one or more of the complex members and in this way, protein complex formation can be similar to phosphorylation. These complexes are a cornerstone of many (if not most) biological processes and together they form various types of molecular machinery that perform a vast array of biological functions. Individual proteins can participate in the formation of a variety of different protein complexes. Different complexes perform different functions, and the same complex can perform very different functions that depend on a variety of factors. Some of these factors are:
♦ Which cellular compartment the complex exists in
♦ Which stage in the cell cycle the complexes are present
♦ The nutritional status of the cell
♦ Others
Many protein complexes are well understood, particularly in the model organism Saccharomyces cerevisiae (a strain of yeast). For this relatively simple organism, the study of protein complexes is now being performed genome wide and the elucidation of most protein complexes of the yeast is undergoing.
The molecular structure of protein complexes can be determined by experimental techniques such as X-ray crystallography or nuclear magnetic resonance. Increasingly the theoretical option of protein-protein docking is also becoming available.
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