A nuclear magnetic resonance investigation of the influence of distal glutamine on structural properties of Lucina pectinata hemoglobin I.

摘要

The architecture of proteins is fascinating, yet enigmatic. The knowledge of the structure and properties of non-vertebrate hemoglobins, such as the hemoglobin I (HbI) from the clam Lucina pectinata, can help us create diverse models in terms of show proteins perform their functions in living organisms. HbI contains three phenylalanine (Phe) residues: Phe29(B10), Phe43(CD1), and Phe68(E11), and it has a glutamine residue, Gln64, at the distal position E7. In this respect, Nuclear Magnetic Resonance (NMR) was used to study the stabilization of heme bound ligands in the heme pocket of Hbl. The one-dimensional proton (1H) spectra of metHbICN and metHbIH₂S showed signals resonance at 13.80 ppm and 14.21 ppm, respectively. The chemical exchangeable proton behavior of the amide group was used to assign these signals to the N_ϵH Gln64(E7). Analysis of the steady-state Nuclear Overhauser Experiment (NOE) and the two dimensional data confirm these assignments and provided information about the distal environment of the heme cavity. Our result was compared with the chemical shifts of the met-cyano complexes of elephant, sperm whale triple mutant, and shark myoglobin to demonstrate the stabilization method of iron-ligand in HbI. The results establish that the carbonyl group of Gln64(E7) points toward the bound ligand, stabilizing the H₂S by hydrogen bonding, but does not exhibit local conformational change to stabilize other ligands, such as O₂, CN −, and CO.