![]() Hydrophobic amino acids will tend to be kept inside the structure, with little or no contact with the surrounding water conversely, polar or charged amino acids will be often exposed to solvent. In fact, many random amino acid sequences only acquire ill-defined structures (molten globules) or no structure at all. This seems to mean that biological proteins somehow evolved to properly fold. It is known now that the unfolded state still retains key long-range interactions and that the local propensity of the sequence to fold in a given secondary structure element narrow the "search" in the so-called conformational space. As of today molecular dynamics simulations are giving invaluable hints on the first stages of the folding process. Many local and non-local interactions take part in the process, and the space of possible structures is enormous. The path followed by the protein in the potential energy landscape is far from obvious, however. Meanwhile, protein folding is a thermodynamically driven process: that is, proteins fold by reaching their thermodynamically most stable structure. Specialized proteins called chaperones assist in the folding of other proteins. The process of folding often begins co-translationally, so that the N-terminus of the protein begins to fold while the C-terminal portion of the protein is still being synthesized by the ribosome. This conclusion was by no means obvious, given the complexity of the folding process and the paucity of biochemical knowledge at the time. In 1954 Christian Anfinsen demonstrated that the folding of a protein in a given environment depends only on its primary structure - the amino acid sequence. An unfolded polymer exists are random coils, each copy of an unfolded polymers will have different conformation, yielding a mixture of many possible conformation.įolding depends only on primary structure Moreover, the ability of biological polymers such as protein fold into well-defined structures is remarkable thermodynamically. That's why we're still almost unable to predict the folding of a given polypeptide chain ab initio.Protein folding problem is that scientist still has failed to crack the code that governs folding. There are literally millions of possible three-dimensional configurations, often with minimal energetic differences between them. It can be viewed as a complex compromise between the different chemical interactions that can happen between the amino acid sidechains, the amidic backbone and the solvent. ![]() Protein folding is commonly a fast or very fast process, often but not always reversible, taking no more than a few milliseconds to occur. 9.4 Less common secondary structure elements.8.4 Super-tertiary structure (protein modules).4 Intramolecular forces in protein folding.2 Folding depends only on primary structure.
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