A dodecamer of globin chains is the principal functional subunit of the extracellular hemoglobin of Lumbricus terrestris

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- .…”

“…On the basis of the observation of a dodecamer lacking linker chains as a product of Lumbricus Hb dissociation, we proposed a bracelet model for its quaternary structure, consisting of 12 dodecamers (12 × [ a + b + c ] 3 [ d 3 ]), decorating a bracelet or framework of 30−40 linkers. , On the basis of the most recent Hb mass of 3.55 × 10 6 , the 12 dodecamers (2.13 × 10 5 × 12 = 2.56 × 10 6 ), account for ∼72% of the total mass, in excellent agreement with the iron and heme contents (sections II.B and II.F). This model also accounts for the low α-helical content deduced from CD spectra (∼40%) ,, and appears to hold for all annelid and vestimentiferan Hbs for which ESI-MS and STEM mass data have become available recently. ,,− It should be noted that in the case of Lumbricus Hb, even with the ESI-MS masses of its subunits, it is impossible to be sure of the number of linker subunits, since the two likely possibilities, 36 and 42, both provide masses within the experimental error of the total Hb mass .…”

Modeling of the Dodecameric Subunit of Lumbricus Hemoglobin

“…Hb, recent considerations [3] provide evidence for the validity of the given mass for the HBL assembly consisting of 144 globins and 36 nonglobin linker chains. The assembled chains form a molecule with D 6 symmetry [4,5], and the validity of the previous "bracelet" model [6,7] has been proven meanwhile. 12 subassemblies of globin chains are arranged in two hexagonal layers, and, as a consequence of this assemblage, a central cavity is formed in the particle center.…”

“…The dissociation behavior of L.t. Hb was investigated at extremes of pH and in the presence of several dissociating agents (e.g., [6,7,[22][23][24]). A variety of dissociation and re-association experiments resulted in the observation of a 9-10 S species which was considered to represent one-twelfth protomer, an approx.…”

Small Angle X-Ray Scattering Studies and Modeling of Eudistylia vancouverii Chlorocruorin and Macrobdella decora Hemoglobin

“…Two models have been proposed to explain the architecture of Lumbricus Hb: The first model comprises 24 octameric subassemblies of globin chains and 24 linker chains (Ownby et al, 1993). In the second, the so-called ''bracelet model'' (Vinogradov et al, 1986(Vinogradov et al, , 1991Martin et al, 1996a,b), 12 dodecameric 200-kDa subunits, each composed of three monomeric and three trimeric heme-containing globin chains, and 36 heme-deficient linker chains form the HBL complex with a total mass of ;3.5 MDa.…”