Hierarchy of globin complexes

The Multi-hemoglobin System of the Hydrothermal Vent Tube Worm Riftia pachyptila

“…monomeric globin chains (ϳ16 kDa), linker chains (ϳ26 kDa), and trimers or dimers of globin chains (ϳ53 or 32 kDa, respectively). In Riftia, the linker chains L1-L4 are only found in V1 Hb, in agreement with the idea that they are required for the maintenance of the HBL structure by analogy with annelid HBL Hbs, such as earthworm Lumbricus (13) and the leech Macrobdella (37), and annelid chlorocruroin, such as the polychaete Eudistylia (38). Riftia and Lamellibrachia (6) HBL Hbs most closely resemble that of the achaete Macrobdella Hb (14).…”

Giant Hexagonal Bilayer Hemoglobins

“…Following the determination of the smallest subunits and number of polypeptide chains by complete dissociation of Lumbricus Hb, we sought to identify larger subunits via partial dissociation of the HBL structure, at pH > 8, at pH < 6, and at neutral pH in the presence of urea, Gdm·Cl, and chaotropic agents. , These studies provided unequivocal evidence for a functional ∼2 × 10 5 subunit having the stoichiometry [ a + b + c ] 3 [ d 3 ], deficient in linker chains and which could be formed spontaneously upon mixing of the isolated trimer [ a + b + c ] and chain d − A recent study of the dissociation kinetics of Lumbricus Hb at alkaline pH and at neutral pH in the presence of urea, Gdm salts, and heteropolytungstate cations has demonstrated that the dodecamer is observed at all stages of the dissociation, the extent of dissociation decreasing in the order Gdm·SCN > Gdm·Cl > urea > Gdm·OAc and [BaAs 4 W 40 O 140 ] 27- > [SiW 11 O 39 ] 8- > [NaSb 9 W 21 O 86 ] 18- . The kinetics appear to be heterogeneous, with at least three exponentials required to provide acceptable fits in the case of urea and Gdm·Cl and two in the case of the heteropolytungstates .…”

Ligand binding and slow structural changes in chlorocruorin from Spirographis spallanzanii

“…The structure proposed for Chi from E. vancouverii supports the dodecamer as the functional unit; the myoglobin-like monomers are, however, assembled in disulfide-bonded tetramers, and the assembly of three tetramers builds up the dodecamer (Qabar et al, 1991). Thus, even though the hemeheme distance in the tetramer is possibly similar to that in human hemoglobin, the transfer of information between the hemes in a dodecamer is likely to be uneven, each subunit interacting more strongly with the other subunits of the same tetramer.…”

“…In contrast to hemoglobin and erythrocruorin, Chi is green, because its heme group is different with a formyl group at position 2 of the porphyrin macrocycle (where protoporphyrin IX has a vinyl group). The assembly of Chi and of the closely related erythrocruorins involves interactions between myoglobin-like oxygen binding subunits with , = 17 kDa and the so-called linker chains with Mt = 30 kDa; 12 hexadecamers or dodecamers, which contain only the oxygen-binding subunits, are linked together by the linker chains in the superimposed hexagonal layers observed in disk shaped particles by electron microscopy (Guerritore et al, 1965;Qabar et al, 1991). The presence of the linker chains lowers the iron content of chlorocruorins and erythrocruorins relative to that of hemoglobins and myoglobins (0.25% vs 0.33%); in fact, the and partially characterized dodecameric subunits of Chi from Eudistylia vancouverii (Qabar et al, 1991;Gibson et al, 1992) were shown to be cooperative (from the kinetics of combination with carbon monoxide); moreover, it was possible to split them into three tetramers, which bind oxygen and CO reversibly.…”