Levels of the structural organization of the protein molecule: the secondary structure of the protein

The basis of the structure of proteins and proteins is a polypeptide chain, and the protein molecule can consist of one, two or more chains. Nevertheless, the physical, biological and chemical properties of biopolymers are determined not only by a common chemical structure, which may be "meaningless", but also by the presence of other levels of organization of the protein molecule.

The primary structure of the protein is determined by the quantitative and qualitative amino acid composition. Peptide bonds are the basis of the primary structure. For the first time this hypothesis was expressed in 1888 by A. Ya. Danilevsky, and later his assumptions were confirmed by peptide synthesis, which E. Fisher carried out. The structure of the protein molecule was studied in detail by A. Ya. Danilevsky and E. Fisher. According to this theory, protein molecules consist of a large number of amino acid residues, which are connected by peptide bonds. The protein molecule may have one or more polypeptide chains.

In the study of the primary structure of proteins, chemical agents and proteolytic enzymes are used. Thus, using the Edman method it is very convenient to identify terminal amino acids.

The secondary structure of the protein demonstrates the spatial configuration of the protein molecule. There are the following types of secondary structure: alpha-helical, beta-helical, collagen helix. Scientists have determined that the alpha-helix is most characteristic for the structure of peptides.

The secondary structure of the protein is stabilized by hydrogen bonds. The latter arise between hydrogen atoms connected to the electronegative nitrogen atom of one peptide bond and the carbonyl oxygen atom of the fourth amino acid from it, and they are directed along the helix. Energy calculations show that in the polymerization of these amino acids, the right alpha helix, which is present in native proteins, is more effective.

Secondary structure of protein: beta-fold structure

The polypeptide chains in the beta folds are completely elongated. Beta folds are formed by the interaction of two peptide bonds. This structure is characteristic of fibrillar proteins (keratin, fibroin, etc.). In particular, beta-keratin is characterized by the parallel arrangement of polypeptide chains, which are additionally stabilized by interchain disulfide bonds. In silk fibroin, adjacent polypeptide chains are antiparallel.

Secondary structure of protein: collagen spiral

The formation consists of three spiral chains of tropocollagen, which has the shape of a rod. The spiral chains are twisted and form a supercoiling. The helix is stabilized by hydrogen bonds arising between the hydrogen of the peptide amino groups of the amino acid residues of one chain and the oxygen of the carbonyl group of the amino acid residues of the other chain. The presented structure gives collagen high strength and elasticity.

Tertiary structure of the protein

Most proteins in the native state have a very compact structure, which is determined by the shape, size and polarity of the amino acid radicals, as well as by the sequence of amino acids.

Hydrophobic and ionogenic interactions, hydrogen bonds, etc., have a significant effect on the formation of the native conformation of the protein or its tertiary structure. Under the action of these forces, a thermodynamically expedient conformation of the protein molecule and its stabilization is achieved.

Quaternary structure

This kind of molecule structure arises as a result of the association of several subunits into a single complex molecule. The structure of each subunit includes the primary, secondary and tertiary structures.