Hemoglobins from Mycobacterium tuberculosis and Campylobacter jejuni: a comparative study with resonance Raman spectroscopy.

Three groups of hemoglobins (Hbs) have been identified in unicellular organisms: (1) the truncated Hbs (trHb) that display a novel two-over-two alpha-helical structure, (2) the flavohemoglobins (FHb) that comprise a Hb domain with a classical three-over-three alpha-helical structure and a covalently attached flavin-containing reductase domain, and (3) the single-domain Hbs (sdHb) that exhibit high sequence homology and structural similarity to the Hb domain of FHb. On the basis of phylogenetic analysis, the trHbs can be further divided into three subgroups: TrHb-I, TrHb-II, and TrHb-III. The various classes of Hbs may coexist in the same organism, suggesting distinct functions for each class of Hb. This chapter reviews the structural and functional properties of a TrHb-I (trHbN) and a TrHb-II (trHbO) from Mycobacterium tuberculosis, as well as a TrHb-III (trCtb) and a sdHb (Cgb) from Campylobacter jejuni on the basis of resonance Raman spectroscopic studies.