![]() So we need the computational predictive tools to narrow the widening gap. The increasing rate of the protein sequence number is much greater than that of the known protein structure number. ![]() Meanwhile, the capacity of databases (e.g., PDB) collecting protein tertiary crystal structures increases slowly. The elucidation of the protein peptide chain-folding mechanisms is called decoding the second biological code.Īs the human genome and other species genome sequencing plan start and finish, the capacity of databases (e.g., SWISS-PROT) collecting protein sequence increases exponentially. How does protein fold from primary structure into active natural tertiary structure is waiting to be answered. The development and research of life science show that protein peptide chain-folding mechanism is the most important problem to be solved. ![]() The Significance of Protein Structure Prediction The structure of the β-turn is determined by the dihedral angel ( ) made of the second residue and third residue. The oxygen on C=O of the first residue and hydrogen on the N–H of the fourth residue form hydrogen bond. In this structure, the backbone folds in a degree of 180°. ![]() It is composed of four successive amino acids. Β-Turn can also be called reverse turn, β-bend, and hairpin structure. In random coils, β-turn is a very important structure. For most globins, they often contain a great amount of random coils besides α-helix and β-sheet. Random coils mean the irregular peptide chain. In the backbones of polypeptide chain, the structures which are different from the α-helix and β-sheet are called random coil. The polarization of the peptide chain is opposite for the neighboring chains. The N-end of all the peptide chains is in the same direction. The arrangement polarization of its peptide chain (N–C) is unidirectional. Along the long axis of peptide chain, there are repeated units. The hydrogen bonds are almost vertical to the long axis of peptide chains. In the β-sheets, all peptides join in the cross-linking between hydrogen bonds. These polypeptide structures are β-sheet. Hydrogen bond is formed by –NH and C=O on the neighboring peptide backbones. Two or more fully expended polypeptides cluster together laterally. Β-Sheet is another frequently occurrence structure. α-Helix tends to be stable because the hydrogen in NH and the oxygen in the fourth residue CO form hydrogen bond. Tightly curled polypeptide backbone forms the inner side of the stick the side chains expand outside in the form of helix. Local organization of protein backbone is α-helix, β-strand (which assembles into β-sheet), turn, and interconnecting loop. Various Kinds of Protein Secondary Structure Different classes of proteins have various functions. Conjugated proteins can also be subdivided into nucleoprotein, lipoprotein, glycoprotein and mucoprotein, phosphoprotein, hemoprotein, flavoprotein, and metalloprotein. Simple proteins can be subdivided into seven subclasses: albumin, globulin, glutelin, prolamine, histone, protamine, and scleroprotein. They can be divided into soluble fibrins and unsolvable fibrins. Comparatively, fibrins are less symmetric and look like thin sticks or fibers. Globins dissolve easily and can crystallize. Globins are more symmetric and similar to balls or ovals in shape. If proteins are completely composed of amino acids, these proteins are called simple proteins, such as insulin if there are other components, they are named conjugated proteins like hemoglobin.Īccording to the symmetry of proteins, proteins can be divided into globin and fibrin. From the aspect of chemical structures of proteins, proteins can be classified into two classes.
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