2 English reference alpha helix
Note α helix is a three-dimensional structure of a specific helical peptide chain existing in various natural protein (see figure). Due to the needs of wool and leather industry, British and American scientists began to study the insoluble protein of wool, hair, hoof and leather by X-ray diffraction technology in 1930s, and found that they all have regular three-dimensional structures. In the early 1950s, L.C. Pauline first proposed a structural model called α-helix, which well explained the X-ray diffraction pattern of hair. Since then, the alpha helix has been generally regarded as the basic structure of protein molecules.
The main features of α helix structure are as follows: ① the peptide chain advances in the form of spiral coils, each spiral consists of 3.6 amino acids, and the pitch of the coils is 5.44 angstroms; ② The helical structure is stabilized by regularly arranged hydrogen bonds. The arrangement of hydrogen bonds is that N-H of each amino acid residue forms hydrogen bonds with C = O of three amino acid residues on the amino side. The hydrogen-bonded ring thus formed contains 13 atoms. Therefore, the alpha helix is often accurately expressed as a 3.6 13 helix. Helices are generally right-handed and left-handed, and what actually exists in protein molecules is the right-handed helix.
In the late 1950s and early 1960s, J.C. Chendru and M.F. Peroots successively used X-ray diffraction to analyze the three-dimensional structures of crystalline myoglobin and hemoglobin, and then successively analyzed the three-dimensional structures of a large number of protein. These results prove that α helix does exist widely in various protein molecules, but sometimes it deviates from some parameters determined by L.C. Pauling.