Interplay of the H-bond donor-acceptor role of the distal residues in hydroxyl ligand stabilization of Thermobifida fusca truncated hemoglobin

F.P. NICOLETTI; J.P. BUSTAMANTE; E. DROGHETTI; B.D. HOWES; M. FITTIPALDI; A. BONAMORE; P. BAIOCCO; A. FEIS; A. BOFFI; D.A. ESTRIN; G. SMULEVICH

BIOCHEMISTRY

AMER CHEMICAL SOC

Lugar: Washington; Año: 2014 vol. 53 p. 8021 - 8030

0006-2960

The unique architecture of the active site of Thermobifida fusca truncated hemoglobin (Tf-trHb) and other globins belonging to the same family has stimulated extensive studies aimed at understanding the interplay between iron-bound ligands and distal amino acids. The behavior of the heme-bound hydroxyl, in particular, has generated much interest in view of the relationships between the spin-state equilibrium of the ferric iron atom and hydrogen-bonding capabilities (as either acceptor or donor) of the OH- group itself. The present investigation offers a detailed molecular dynamics and spectroscopic picture of the hydroxyl complexes of the WT protein and a combinatorial set of mutants, in which the distal polar residues, TrpG8, TyrCD1, and TyrB10, have been singly, doubly, or triply replaced by a Phe residue. Each mutant is characterized by a complex interplay of interactions in which the hydroxyl ligand may act both as a H-bond donor or acceptor. The resonance Raman stretching frequencies of the Fe - OH moiety, together with electron paramagnetic resonance spectra and MD simulations on each mutant, have enabled the identification of specific contributions to the unique ligand-inclusive H-bond network typical of this globin family.