Abstract:
Proteins are the most essential components of a living system. Their functions
range from catalysis, transporting molecules and ions across cell membranes thereby
maintaining electrochemical potentials in intra- and extracellular regions, signal
transduction, and providing rigidity to cells and tissues. Proteins are constituted by
amino acids that are covalently linked to each other to form a polypeptide chain. [1]
The primary structure of a protein is the sequence of amino acids along the polymer.
To a good extent, the sequence determines the structure of the protein. [2] The long
polypeptide chain folds to form local structures, called the secondary structure of
a protein. Among several secondary structures of a protein, -helix and -sheet
are prominent. Other than these two, there are small 3/10-helices and random
coils that connect the -helices and -sheets to produce a proper fold which is the
tertiary structure of a protein. [3] In many cases, a number of such tertiary structures
associate to form a quaternary structure. A quaternary structure can be formed
by the assembling of either homomeric subunits or heteromeric subunits. [1, 3] A
typical example of a quaternary structure is hemoglobin consisting of two 2 2-units
of myoglobins.
