Bridging Theory and Experiment to Address Structural Properties of Truncated Haemoglobins: Insights from Thermobifida fusca HbO

B.D. HOWES; L. BOECHI; A. BOFFI; D.A. ESTRIN; G. SMULEVICH

Advances in Microbial Physiology

Academic Press

Lugar: Oxford; Año: 2015; p. 85 - 126

n this chapter, we will discuss the paradigmatic case of Thermobifida fusca (Tf-trHb) HbOin its ferrous and ferric states and its behaviour towards a battery of possible ligands. This choice was dictated by the fact that it has been one of the most extensively studiedtruncated haemoglobins, both in terms of spectroscopic and molecular dynamics stud-ies. Tf-trHb typifies the structural properties of group II trHbs, as the active site is char-acterized by a highly polar distal environment in which TrpG8, TyrCD1, and TyrB10provide three potential H-bond donors in the distal cavity capable of stabilizing theincoming ligands. The role of these residues in key topological positions, and their inter-play with the iron-bound ligands, has been addressed in studies carried out on the CO,F À , OH À , CN À , and HS À adducts formed with the wild-type protein and a combinatorialset of mutants, in which the distal polar residues, TrpG8, TyrCD1, and TyrB10, have beensingly, doubly, or triply replaced by a Phe residue. In this context, such a complete anal-ysis provides an excellent benchmark for the investigation of the relationship betweenprotein structure and function, allowing one to translate physicochemical properties ofthe active site into the observed functional behaviour. Tf-trHb will be compared withother members of the group II trHbs and, more generally, with members of the othertrHb subgroups.