β-Pleated Sheet

The second type of secondary structure is the β-pleated sheet, in which the backbone is extended in a zigzag structure resembling pleats.  The H-bonding in a β-pleated sheet occurs between the adjacent peptide chains.

12.8.3 Tertiary Structure of Protein

The tertiary structure of a protein describes the three-dimensional arrangement of all the atoms. In solution, proteins fold to maximize their stability through interactions include disulfide bonds, hydrogen bonds, electrostatic attractions and hydrophobic interactions. Scheme 4 illustrates an

Scheme 4. Stabilizing interactions for the tertiary structure of protein.

 

12.8.4 Quaternary Structure of Protein

Some proteins have more than one peptide chain and the individual chain is called a subunit. The subunits are held together by intractions such as hydrophobic intraction, H-bonding, and electrostatic attractions. The quarternary structure of a protein describes the way the subunits are arranged in space. Scheme 4 shows the structure of hemoglobin which is a tetrameric structural protein comprising two α and two β subunits.

 

Scheme 5. Quaternary Protein Structure: Three-Dimensional Arrangement of Subunits.