Effects of active site mutations in haemoglobin I from Lucina pectinata: a molecular dynamic study

Haemoglobin I from Lucina pectinata is a monomeric protein consisting of 142 amino acids. Its active site contains a peculiar arrangement of phenylalanine residues (PheB10, PheCD1 and PheE11) and a distal Gln at position E7. Active site mutations at positions B10, E7 and E11 were performed in deoxy haemoglobin I (HbI), followed by 10 ns molecular dynamic simulations. The results showed that the mutations induced changes in domains far from the active site producing more flexible structures than the native HbI. Distance analyses revealed that the heme pocket amino acids at positions E7 and B10 are extremely sensitive to any heme pocket residue mutation. The high flexibility observed by the E7 position suggests an important role in the ligand binding kinetics in ferrous HbI, while both positions play a major role in the ligand stabilisation processes. Furthermore, our results showed that E11Phe plays a pivotal role in protein stability.