ABSTRACT

Proteins are originally believed that one gene codes only for a single protein, but in the human genome only 20000-25000 genes code for >100000 proteins that constitute our proteome, the sum of all proteins in human body. Proteins are polymers of amino acids that are linked via amide bonds, also termed peptide bonds. Analysis of high-resolution protein crystal structures with well-defined electron density for the side chains has shown that the amino acid side chains adopt preferred conformations or rotamers. Post-translational modifications can be covalent or non-covalent, permanent or transient, general for many proteins or specific to a single class of proteins. Small molecule or ligand binding to proteins and other macromolecules follows the same principles as protein-protein interactions, including shape and biophysical complementarity to maximize the number of hydrophobic contacts and H-bonds. Substantial fraction of the protein may be in the unfolded state at physiological temperatures. The presence of unfolded proteins in the cell is often linked to disease.