The Three-Dimensional Structure of Proteins

Any protein in a functionally folded conformation is called a native protein and the stability of the protein depends on its ability to maintain this state. Naturally occurring proteins are indeed only slightly stable, which means that the Gibbs free energy for separating the folded and unfolded state is relatively small under biological conditions. Any given polypeptide chain desirably exhibits an infinite conformation and thus the unfolded state of the protein is characterized by a high conformational entropy. This high entropy and the hydrogen bonding interaction of the groups in the polypeptide chain with water maintains the unfolded state.

The specific sequence of amino acids results in a unique three dimensional structure of the protein and the three dimensional structure of the protein is related to that function. There are also simple structural molecules such as fibers formed by protein collagen. Proteins can bind to other proteins and simple molecules and act as enzymes (without altering the structure of the protein itself) by promoting chemical reactions within the binding protein. Protein structure is dynamic and protein hemoglobin turns slightly different as it promotes trapping, transportation and release of oxygen molecules in mammalian blood.

Enzymes called chaperone proteins further change the three-dimensional structure of proteins by folding in a specific manner. The function of a protein depends on its shape, so the three-dimensional structure of the protein is the most important property. It can react with other molecules only when two molecules like key and lock work in concert. The three-dimensional structure of a fully folded protein is its tertiary structure. The cause of diseases such as prion, mad cow disease, scrapie, Creutzfeldt-Jakob disease is protein. Primary and secondary structures are almost identical to proteins normally expressed in our brain cells, but the tertiary structure is different - they are folded into different shapes. When a prion enters a healthy brain cell it can denature (unravel) the native protein and reform it into the same form as a prion.

Tertiary structure refers to the three-dimensional structure of a single protein molecule. The α-helix and β-sheet are folded into tight beads. Folding is promoted by nonspecific hydrophobic interactions (buried hydrophobic residues from water), but the structure is such that a part of the protein domain is in place by specific tertiary interactions such as salt bridges, hydrogen, etc. It stabilizes only when it is fixed. Binding, closest packing of side chains and disulfide bonds. Since cytosol is usually a reducing environment, disulfide bonds are very rare in cytoplasmic proteins