Protein folding, unfolding and misfolding: role played by intermediate States.

Most proteins fold into their native structure through well defined pathways which involve a limited number of transient intermediates. Intermediates play a relevant role in the folding process; many diseases of genetic nature are in fact coupled with protein misfolding due to formation of stable, inactive intermediate species of the protein. This review deals with a number of diseases associated with protein misfolding and briefly describes the mechanism(s) responsible, at molecular level, for such pathologies. It is also considered the (native <--> molten globule) transition, recently observed for some proteins, in which a native protein converts into a stable compact intermediate state able to carry out distinct physiological functions inside the cell. A non-native compact form of cyt c, for example, appears to have a role in the programmed cell death (apoptosis) after that the protein is released from the mitochondrion, and non-native forms of the same protein appear involved in some of the disorders attributed to amyloid formation.