= Protein folding
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<Protein folding> is the process by which a <polypeptide chain> acquires an organized spatial arrangement. The interactions of its <amino acid residues> with one another and the surroundings favor some arrangements over others. <Protein folding> can bring chemically useful groups together at an <active site> without changing their order along the <protein backbone>. Its importance is practical: knowing a sequence alone does not tell us whether a sample has the structure needed for function. See https://www.ncbi.nlm.nih.gov/books/NBK9843/[Cooper: acquiring functional protein structure].
The <ribonuclease A refolding experiment> showed that an isolated <protein> could recover its native properties without a pre-existing folded template under suitable laboratory conditions. Anfinsen interpreted this through a thermodynamic hypothesis: the native arrangement minimizes the whole system's <Gibbs free energy> in the appropriate environment. His Nobel lecture was delivered on 11 December 1972 and published in Science in 1973. The specified environment is part of the claim, not a disposable qualification. See https://web.iitd.ac.in/~amittal/1973_Anfinsen_Science.pdf[Anfinsen, Principles that Govern the Folding of Protein Chains, Science 181, 223–230 (1973): Nobel lecture, especially p. 223].
This does not imply that every <protein> rapidly folds unaided. <Molecular chaperones> can assist <protein folding> and reduce <protein aggregation>; required partners, surroundings and time still matter. Goloubinoff and colleagues' 1989 reconstitution experiments demonstrated assistance from two <molecular chaperones> and <ATP> in recovering an active <enzyme> from unfolded chains. This is experimental evidence that assistance can matter even when the chains already have their specified sequences. See https://www.nature.com/articles/342884a0[Goloubinoff, Christeller, Gatenby and Lorimer, 1989: chaperone-assisted reconstitution of an active enzyme].
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