Abstract:
Proteins in nature have evolved to perform specific functions. The functional properties of proteins depend upon their three-dimensional structures. The three-dimensional structure arise because particular sequences of amino acids in polypeptide chains fold to generate, from primary chains, compact protein folding with specific three-dimensional structures. (1)To understand the biological function of proteins we would therefore like to be able to deduce or predict the three-dimensional structure from the amino acid sequence. Many models of how proteins might fold have been proposed, with varying degrees of detail and folding predictions that are capable of being tested. However, in spite of considerable efforts over the last 25 years, the protein folding problem is still unsolved and remains one of the most urgent intellectual challenges in molecular biology. (1) Thus, most have stressed roles for secondary structure, since such regular local conformations seem most likely to be predictable, stable in isolation and occur at early stages of folding (2, 3).The fundamental reason why the protein folding problem remains unsolved lies in the fact that there are 20 different amino acids and therefore a vast number of ways in which similar structural domains can be generated in proteins by different amino acid sequences. Since the three-dimensional structures of individual proteins cannot be predicted, they have instead to bedetermined experimentally by X-ray crystallography or nuclear magnetic resonance (NMR) techniques. Even though X-ray crystallography techniques may be laborious, expensive, and time consuming over the past 30 years the structures of around 500 proteins have been solved by X-ray methods . This has generated a body of information from which a set of basic principles ofprotein structure has emerged. These principles make it easier for us to understand how protein structure is generated, to identify common structural themes, to relate structure to function, and to see fundamental relationships between different proteins. (1)In this paper relationships among primary, secondary, and tertiary protein structure, approaches to predict the tertiary protein folding using either the X-ray crystallography technique or the method based on the amino acid sequence, and problems of these approaches will be examined. Also some models of how specific proteins might fold will be mentioned in the end of this paper.