Elementary plant Biochemistry and Biotechnology (2+1)

Salt-linkages

Salt-linkages (electrostatic forces; ionic bonds)

 

• Salt linkages are due to the interaction between amino groups of basic amino acids and the carboxyl group of acidic amino acids present in the R group

Disulfide bonds (S-S linkages)

• The S-S linkages are formed by the oxidation of sulfhydryl (-SH) group of two cysteine side chains

Hydrophobic bonds

• Hydrophobic bonds are formed as a result of interaction between non-polar side chains

Dipole-dipole interaction

• This interaction occurs between polar unionized side chains.
• The folding of a polypeptide chain due to different covalent and non-covalent interactions is shown below.
• Out of the above bonds, the disulfide bond (covalent bond) is the strongest and cannot be affected by solvent, pH, temperature and salts whereas the above conditions.
• The disulfide bond can be split and reformed by oxidation/reduction respectively.
• The tertiary structure gains special importance in the case of enzymes

Domain

• Domains are structurally independent units that have the characteristics of a small globular protein.
  Domains often have a specific function such as the binding of a small molecule.
• A long peptide strand of a protein will often fold into multiple, compact semiindependent folded regions or domains.
  
• Each domain having a characteristic spherical geometry with a hydrophobic core and polar surface very much like the tertiary structure of a whole globular protein.
• The domains of a multidomain protein are often interconnected by a segment of polypeptide chain lacking regular secondary structure.
  
• In enzymes with more than one substrate or allosteric effector sites the different binding sites are often located in different domains.
  
• In multifunctional proteins, the different domains perform different tasks.