<P> The study of protein folding has been greatly advanced in recent years by the development of fast, time - resolved techniques . Experimenters rapidly trigger the folding of a sample of unfolded protein and observe the resulting dynamics . Fast techniques in use include neutron scattering, ultrafast mixing of solutions, photochemical methods, and laser temperature jump spectroscopy . Among the many scientists who have contributed to the development of these techniques are Jeremy Cook, Heinrich Roder, Harry Gray, Martin Gruebele, Brian Dyer, William Eaton, Sheena Radford, Chris Dobson, Alan Fersht, Bengt Nölting and Lars Konermann . </P> <P> Proteolysis is routinely used to probe the fraction unfolded under a wide range of solution conditions (e.g. Fast parallel proteolysis (FASTpp). </P> <P> Single molecule techniques such as optical tweezers and AFM have been used to understand protein folding mechanisms of isolated proteins as well as proteins with chaperones . Optical tweezers have been used to stretch single protein molecules from their C - and N - termini and unfold them to allow study of the subsequent refolding . The technique allows one to measure folding rates at single - molecule level; for example, optical tweezers have been recently applied to study folding and unfolding of proteins involved in blood coagulation . von Willebrand factor (vWF) is a protein with an essential role in blood clot formation process . It discovered--using single molecule optical tweezers measurement--that calcium - bound vWF acts as a shear force sensor in the blood . Shear force leads to unfolding of the A2 domain of vWF, whose refolding rate is dramatically enhanced in the presence of calcium . Recently, it was also shown that the simple src SH3 domain accesses multiple unfolding pathways under force . </P> <P> A protein is recognized as misfolded if it cannot achieve the native state of a protein . This can be due to unwanted mutations in the amino acid sequence or could be caused through errors in the folding process . The misfolded protein typically contains beta - sheets that are organized in a polymeric arrangement known as a cross-beta structure . The abnormal proteins that are rich in beta sheet structure become partially resistant to proteolysis . Part of the reason is because beta sheets are stabilized by intermolecular interactions, therefore the misfolded proteins will have a high tendency to form oligomers and larger polymers . Also the accumulation of misfolded proteins can lead to an accumulation of protein aggregates or oligomers in the cell . The increased levels of aggregated proteins in the cell leads to formation of amyloid - like structures which can cause degenerative disorders and cell death . The amyloids are fibrillary structure that contain intermolecular hydrogen bonds, which are highly insoluble, and made from converted protein aggregates . Therefore, the proteasome pathway may not be efficient enough to degrade the misfolded proteins prior to aggregation . Misfolded proteins can interact with one another and form structured aggregates and gain toxicity through intermolecular interactions . </P>

All proteins have a minimum of how many levels of protein structure