Differences and Similarities in Protein and Nucleic Acid Structures and Their Biological Interactions.

Protein and nucleic acid play central roles in biology and pharmaceuticals. Both share a similar architecture made of a backbone and side chains. Protein has a peptide backbone and various side chains, whereas nucleic acid has a phosphate backbone and aromatic side chains. However, they are significantly different in the chemical properties of the backbone and side chains. The protein backbone is uncharged, while nucleic acid backbone is negatively charged. The protein side chains comprise widely different chemical properties. On the other hand, the nucleic acid side chains comprise a uniform chemical property of aromatic bases. Such differences lead to fundamentally different folding, molecular interactions and co-solvent interactions, which are the focus of this review. In regular protein secondary structures, the peptide groups form polar hydrogen bonds, making the interior hydrophilic. The side chains of different chemical properties are exposed on the outside of the protein secondary structures and participate in molecular and co-solvent interactions. On the other hand, hydrophobic/aromatic nucleobase side chains are located inside the typical double helix or quadruplex structures. The charged phosphate groups of the nucleic acid backbone are located outside, participating in electrostatic interactions. The nucleobases are also involved in molecular interactions, when exposed in breaks, hairpins, kinks and loops. These structural differences between protein and nucleic acid confer different interactions with commonly used co-solvents, such as denaturants, organic solvents and polymers.