Several proteins, after their synthesis in cellular environment, often misfold and aggregate and need folding aids.Aggregation of proteins, wrong disulfide bond formation, and cis-trans isomerization of prolines are the major impediments preventing the native structure formation, leading to a number of age-related diseases like Cataract,Alzheimers and Parkinsons.The same is true for in vitro refolding of proteins from already aggregated states or from inclusion bodies produced during recombinant protein production.Nature has, nonetheless, devised efficient strategies to counter such undesirable processes by employing protein-based molecular chaperones, disulfide isomerases, and prolyl cis-trans isomerases.