Protein–protein interaction
Introduction


[thumb\|The horseshoe shaped ribonuclease inhibitor (shown as wireframe) forms a protein–protein interaction with the ribonuclease protein. The contacts between the two proteins are shown as coloured patches.](/wiki/File:1dfj_RNAseInhibitor-RNAse_complex.jpg "1dfj RNAseInhibitor-RNAse complex.jpg")
**Protein–protein interactions** (**PPIs**) are physical contacts of high specificity established between two or more [protein](/wiki/Protein "Protein") molecules as a result of biochemical events steered by interactions that include [electrostatic forces](/wiki/Electrostatic_forces "Electrostatic forces"), [hydrogen bonding](/wiki/Hydrogen_bond "Hydrogen bond") and the [hydrophobic effect](/wiki/Hydrophobic_effect "Hydrophobic effect"). Many are physical contacts with molecular associations between chains that occur in a cell or in a living organism in a specific biomolecular context.

Proteins rarely act alone as their functions tend to be regulated. Many molecular processes within a cell are carried out by [molecular machines](/wiki/Molecular_machine "Molecular machine") that are built from numerous protein components organized by their PPIs. These physiological interactions make up the so\-called [interactomics](/wiki/Interactome "Interactome") of the organism, while aberrant PPIs are the basis of multiple aggregation\-related diseases, such as [Creutzfeldt–Jakob](/wiki/Creutzfeldt%E2%80%93Jakob_disease "Creutzfeldt–Jakob disease") and [Alzheimer's diseases](/wiki/Alzheimer%27s_disease "Alzheimer's disease").

PPIs have been studied with [many methods](/wiki/Methods_to_investigate_protein%E2%80%93protein_interactions "Methods to investigate protein–protein interactions") and from different perspectives: [biochemistry](/wiki/Biochemistry "Biochemistry"), [quantum chemistry](/wiki/Quantum_chemistry "Quantum chemistry"), [molecular dynamics](/wiki/Molecular_dynamics "Molecular dynamics"), [signal transduction](/wiki/Signal_transduction "Signal transduction"), among others. All this information enables the creation of large protein interaction networks – similar to [metabolic](/wiki/Metabolic_network "Metabolic network") or [genetic/epigenetic networks](/wiki/Genetic_networks "Genetic networks") – that empower the current knowledge on [biochemical cascades](/wiki/Biochemical_cascade "Biochemical cascade") and molecular etiology of disease, as well as the discovery of putative protein targets of therapeutic interest.


Can you list all the methods that have been used to study protein–protein interactions?