Three-dimensional structure of a hemichrome hemoglobin fromCaudina arenicola

Abstract

The structure of a monomeric hemichrome form of an invertebrate hemoglobin, Hb-C chain, from Caudina arenicola has been refined to an R value of 0.16 using the data from 5.0 to 2.5 ,~ resolution (R = 0.21 from 10.0 to 2.5 ,~ resolution). Hb-C crystallizes in space group P2 l with cell constants a =45.74, b = 45.23 and c = 40.92,~ and/3 = 104.4 ° with two monomers packed in the unit cell (V m = 2.34,~ 3 Da-I). The phases were determined by the multiple isomorphous replacement method with Hg 2+ the major derivative. The structure consists of 157 amino acids with N-and C-terminal regions and eight a-helices forming a heme pocket. The unique feature of this structure is the hemichrome form with the proximal and distal histidines coordinated to the heme Fe atom, which is nearly in the plane of the porphyrin ring. A total of 111 solvent molecules were added to the structure using difference density peaks of at least 3a over background. Interestingly, all the heme groups present in the crystal are nearly coplanar.

Evolution of the Globin Gene Family in Deuterostomes: Lineage-Specific Patterns of Diversification and Attrition

“…Similar modes of liganddependent dissociation/association dynamics are observed in the intracellular and extracellular Hbs of invertebrates (Kitto et al 1998;Riggs 1998;Weber and Vinogradov 2001). For example, in the intracellular Hbs of the sea cucumber, Caudina arenicola, cooperativity stems from ligand-linked association into deoxygenated tetramers and higher level polymers (Bonaventura and Kitto 1973;Mitchell et al 1995;Kitto et al 1998). Similar to the Hbs of cyclostomes and those in many invertebrate taxa, the intersubunit contacts in the coelomic red blood cell Hbs of Caudina are formed by the E and F helices.…”

“…Similar to the Hbs of cyclostomes and those in many invertebrate taxa, the intersubunit contacts in the coelomic red blood cell Hbs of Caudina are formed by the E and F helices. However, crystal structures of Caudina Hbs indicate that the intersubunit contacts involve a unique set of residues (Mitchell et al 1995;Kitto et al 1998).…”

Liganded and unliganded forms of Antarctic fish haemoglobins in polyethylene glycol: crystallization of an R-state haemichrome intermediate

“…2) reveals that the iron is axially linked to both proximal and distal histidyl residues, whereas a CO molecule appears to be linked to the iron. So far, the haemichrome state has only been reported in the monomeric Hb extracted from sea cucumber Caudina arenicola (Mitchell et al, 1995) and in the dimeric non-symbiotic rice Hb (Hargrove et al, 2000). Therefore, airexposed HbTn is the ®rst example of a vertebrate Hb crystallized in the haemichrome state.…”

Structure‐Function Relationships in the Growing Hexa‐Coordinate Hemoglobin Sub‐Family

“…On the proximal side, the azimuthal orientation of the HisF8 imidazole ring is determined, in monomeric hemichrome HbC, by a strong hydrogen bond to residue TyrG5; this interaction is absent in the ferric cyanide derivative of dimeric HbD. Interestingly, the aggregation state of C. arenicola Hbs is unusually ligand-linked, possibly underlying a signal transduction mechanism (48)(49)(50)(51).…”