Protein folding

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Protein folding is the process in which Proteins undergo conformational change. This is where proteins adopt different three dimensional structures depending on their sequence of Amino acids. The process plays an important role in the function of proteins.

Protein folding ultimately occurs in the Tertiary structure. But before that amino acids, the building blocks of proteins, must form Polypeptide chains. This is the Primary structure, where Peptide bonds join amino acids together by linking the alpha amino groups of an amino acid with the alpha carboxyl group of another amino acid [1]. Next comes the secondary structure where the folding of polypeptide chains begin. There are two folds which reoccur in many proteins, namely the Alpha helix and the Beta sheet. The structures of an alpha helix and beta sheet depend on interactions between groups in the polypeptide backbone forming simple proteins. The tertiary structure allows more complex structures to be formed. It is here the alpha helix and beta sheet are folded into three dimensional structures. An example of this structure is Myoglobin, which is a complex globular protein devoid of symmetry [2]. Myoglobin's structure is Amphipathic whereby the interior structure consists of nonpolar residues such as leucine, valine and phenylalanine. However the exterior structure contains charged residues such as aspartate, glutamate and lysine as well as nonpolar residues. In aqueous solution, the interior is Hydrophobic and the exterior is Hydrophilic. This allows the specific structure of myoglobin, allowing it to carry out its function.

It is important for proteins to assume their correct conformation to cellular function. If proteins are not folded properly or there is any disruption in conformation, proteins cannot carry out their function, and as a consequence these proteins introduce disease. Protein conformation can be disrupted by factors such as extreme changes in PH, high temperatures and in the presence of detergents. These factors can Denature proteins such as Enzymes putting an end to its function. Abnormally folded proteins can cause diseases such as the prion disease bovine spongiform encephalopathy (BSE). This disease can occur due to a difference in amino acid bases from a normal cellular protein. These abnormally folded proteins can be associated with degeneration of the brain, dementia and death [3][4][5].

References:

  1. Berg et al (2012). Biochemistry. 7th ed. USA: W.H Freeman and Company. p25-56.
  2. Newcastle University (2013). Compendium. 3rd ed. Essex: Scion publishing Ltd. p7-12
  3. Newcastle University (2013). Compendium. 3rd ed. Essex: Scion publishing Ltd. p7-12
  4. Cooper GM. The Cell: A Molecular Approach. 2nd edition. Sunderland (MA): Sinauer Associates; 2000. Protein Folding and Processing. Available from: http://www.ncbi.nlm.nih.gov/books/NBK9843/
  5. Karadaghi. (2014). Protein Folds and Protein Fold Classification. Available: http://www.proteinstructures.com/Structure/Structure/protein-fold.html.

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