Hydrogen Bonds and Hydrophobic Interactions of Porphyrins in Porphyrin-Containing Proteins

Abstract

Structures of porphyrin-containing proteins from the Protein Data Bank (PDB) Select January 2007, were searched in order to find and systematically characterize hydrogen bonds and hydrophobic interactions of porphyrins in proteins. The results revealed that every porphyrin is involved in at least one hydrogen bond, most of the porphyrins form several, while some of them form up to thirteen hydrogen bonds. In most of the hydrogen bonds propionate groups of porphyrins interact with side-chains of residues. The most frequently observed donor is side chain of arginine. Histidine, lysine, threonine, serine and tyrozine form substantial number of hydrogen bonds too. The study has revealed that hydrophobic interactions are common between porphyrin and protein. Side-chains hydrophobic interactions are more frequent than those with backbone. The average conservation score for the amino acids making hydrogen bonds (7.2) and hydrophobic interactions (7.3) is statistically significantly higher than for the amino acids that are not involved in noncovalent interactions (5.7) with the porphyrin, indicating importance of hydrogen bonds and hydrophobic interactions with the porphyrin.