Proteins that lack definite 3D structure

Not all the proteins have definite 3D structure.There are partially and wholly unstructured proteins have been identified in all kingdoms of life, more commoly in eukaryotic organisms. These proteins are called as protein disorder or intrinsically disordered proteins. These unstructured regions in the proteins are gaining importance since they take part in functional important pathways (eg.Signal transduction pathways) and associated with various disease related Proteins. They are functions classified into four categories: molecular recognition, molecular assembly/disassembly, protein modification and entropic chains.

Protein disorder can be directly studied by NMR or circular dichromism, or indirectly detected by a variety of experimental methods including stretches of missing electron density in X-ray crystallography maps, Raman spectra, hydrodynamic measurements or even limited, time resolved proteolysis. Each one of these methods detects different aspects of disorder resulting in different operational definitions defintions of protein disorder.