<P> The voltage - gated potassium channels in the plasma membrane of a neuron are heteromultimeric proteins composed of four of forty known alpha subunits . Subunits must be of the same subfamily to form the multimeric protein channel . The tertiary structure of the channel allows ions to flow through the hydrophobic plasma membrane . Connexons are an example of a homomultimeric protein composed of six identical connexins . A cluster of connexons forms the gap - junction in two neurons that transmit signals through an electrical synapse . </P> <P> The molecular structure of protein complexes can be determined by experimental techniques such as X-ray crystallography, Single particle analysis or nuclear magnetic resonance . Increasingly the theoretical option of protein--protein docking is also becoming available . One method that is commonly used for identifying the meomplexes immunoprecipitation . Recently, Raicu and coworkers developed a method to determine the quaternary structure of protein complexes in living cells . This method is based on the determination of pixel - level Förster resonance energy transfer (FRET) efficiency in conjunction with spectrally resolved two - photon microscope . The distribution of FRET efficiencies are simulated against different models to get the geometry and stoichiometry of the complexes . </P> <P> Proper assembly of multiprotein complexes is important, since misassembly can lead to disastrous consequences . In order to study pathway assembly, researchers look at intermediate steps in the pathway . One such technique that allows one to do that is electrospray mass spectrometry, which can identify different intermediate states simultaneously . This has led to the discovery that most complexes follow an ordered assembly pathway . In the cases where disordered assembly is possible, the change from an ordered to a disordered state leads to a transition from function to dysfunction of the complex, since disordered assembly leads to aggregation . </P> <P> The structure of proteins play a role in how the multiprotein complex assembles . The interfaces between proteins can be used to predict assembly pathways . The intrinsic flexibility of proteins also plays a role: more flexible proteins allow for a greater surface area available for interaction . </P>

A large structure composed of protein and rna that assembles proteins