A descriptive term used to help visualize the shape of a
protein in the denatured/unfolded state. The
native state of a protein is generally highly organized and well structured. However, if one disrupts the protein with a
chaotrope like
urea, or
guanidine hydrochloride, or subject it to high
temperature, it assumes a random coil
conformation. If a folded protein is like a well formed
knot, the random coil is a pile of string. The random coil is generally a
reversible state, that is to say - if the denaturant is removed or the temperature lowered, the protein may adopt its native state again.
The heirarchy of structures is (generally):
native state <--> molten globule <--> random coil
Some proteins may not have the intermediate stage, or may have several intermediates besides a molten globule.
The random coil is considered a reference state for proteins, where there are no long distance interactions between amino acids. At the most, local interactions with adjacent amino acids in the sequence may occur.
Some proteins have very little structure in their native state. Proteins such as myelin basic protein, (MBP) which are involved in helping maintain the compactness of the myelin wrappings around neuronal axons, have a lot of repulsive charges which keep the protein from assembling into a distinct tertiary fold. The degree of 'randomness' of such proteins is not known, and they may actually adopt a structure when interacting with another partner.