Hemerythrin (Hr) is an O2-carrying protein found in a few phyla of marine invertebrates, most notably sipunculid worms. Characterizations of intermediates and a unifying reaction scheme. The diioxgyen binding pocket is lined with a set of, The hydrophobic environment of the core allows stabilization of the oxy adduct of myohemerythrin, preventing dioxygen from autoxidizing. Little is known of its higher levels of organization, particularly, the structure of its active center. In: Que L Jr (ed) Metal clusters in proteins. Myohemerythrin is a rare monomeric analogue of hemerythrin; myohemerythrin is nonheme iron oxygen-carrying protein found in the retractor muscle tissues of four phyla of invertebrate marine worms. In: Loehr TM (ed) Iron carriers and iron proteins. Oxygen transfer systems involving hemerythrins in sipunculid worms of different ecologies. This fact suggests that polarity, more so than size limits the diffusion of small molecules, including water, into the buried, hydrophobic cavity within myohemerythrin. Unable to display preview. Hemerythrin is an oxygen carrying, non-heme iron metalloprotein of known primary structure. 8 0 obj Eur J Biochem 177: 97–108, LeGall J, Prickril BC, Moura I, Xavier ACV, Moura JJG, Huynh BH (1988) Isolation and characterization of rubrerythrin, a non-heme iron protein from. Biochemistry 27: 1014–1024, Ochi O (1977) X-ray microanalysis on the erythrocytes of sipunculids. 1 0 obj Proc Natl Acad Sci USA 84: 8568–8572, Ghadiri MR, Choi C (1990) Secondary structure nucleation in peptides. The. Leu-103 side chain methyl groups stabilize the bound dioxygen via van der Waals interactions (2). ���('�-�8he$^��X�x��B����=��zD;�0u.����1����@���� �������/������:7a�u�8����`j�P�iΡ(�i3�%� Methemerythin and hemerythrin differ in that methemerythrin is an oxidized form of hemerythrin that no longer can bind dioxygen but still contains the binuclear iron center fixed in the ferric state (13). Apex PDFWriter Methemerythrin from Phascolopsis gouldii is 113 amino acid residues long and this sequence is further processed into a mature form. This process is experimental and the keywords may be updated as the learning algorithm improves. endobj This fact suggests that polarity, more so than size limits the diffusion of small molecules, including water, into the buried, hydrophobic cavity within myohemerythrin. Thus, hemerythrin can bind 8 dioxygen molecules. Not logged in The iron atoms are bound to the protein through the carboxylate side chains of a glutamate and aspartates as well as through five histidine residues. has an approximate 44% sequence similarity to myohemerythrin. <>/ProcSet[/PDF/Text/ImageB]/XObject<>>>/Type/Page>> �B�/��_X�p��g?9i�_�����g��U�:V��\�n��z�~}���|���m#l>|u����չ�Ea�pT����0/J����SZ��FW���K��n9ܡ�h�pl)����l[RkZ1:����譶�Sp��SI��鶷���~�۾(����Y/��F�?�����V��I%�W����h�F��S3�Px��O2x������n��f8՚���6��8�ܬ�o����ޯW�J]��K������o�v�r��]o��M Leu-103 present in the hydrophobic, interhelical core plays a role in stabilizing bound dioxygen with respect to autoxidation; Leu-103 is involved in gating ligand binding to myohemerythrin; rather than sterically gating the binding pocket, the residue gates predominantly through its hydrophobicity (5). The diiron-oxo core accomplishes oxygen binding and transport through a formal 2-electron reduction of the ligand upon binding to the iron center; myohemerythrin and other hemerythrins carry out reduction to the peroxo level (4). The physiological role of Hr is treated in another chapter in this volume. , including His-25, His-54, Asp/Glu-58, His-77, His-106, and Asp-111, are strictly conserved and their spacing agrees with the consensus spacing for the iron ligands in hemerythrin and myohemerythrin; additionally, Leu-103 is also conserved as previously mentioned for all hemerythrins in addition to two other residues integral in the dioxygen binding pocket including Phe-55 and Ile-107 (12). Coord Chem Rev 79: 195–214, Woolery GL, Powers L, Winkler M, Solomon EI, Spiro TG (1984) EXAFS studies of binuclear copper site of oxy-, deoxy-, metaquo-, metfluoro-, and metazidohemocyanin from arthropods and molluscs. Inorg Chem 25: 3514–3516, Armstrong GD, Sykes AG (1986b) Reactions of O, Armstrong GD, Sykes AG (1986c) Active-site chemistry of hemerythrin: kinetic studies on the reduction of metmyohemerythrin from, Board PG, Agar NS, Gruca M, Shine R (1977) Methaemoglobin and its reduction in nucleated erythrocytes from reptiles and birds. 20 0 obj %PDF-1.4
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Hr thus poses interesting contrasts in evolution, physiology, and molecular structure to the more widespread heme oxygen carriers. Most O2 carriers operate via formation of dioxygen complexes, but hemerythrin holds the O2 as a hydroperoxide (HO2, or -OOH ). Hemerythrins differ from other oxygen-binding classes of proteins, including hemoglobins and hemocyanins, in their molecular construction and the complex used in reversibly binding dioxygen (2). J Am Chem Soc 109: 7857–7864, Schulman MP (1957) Incorporation of labeled iron into hemerythrin. Myohemerythrin has a similar structure to other hemerythrins which accounts for its oxygen binding and transporting functions. Studies measuring dioxygen affinities and association and dissociation rates constants have revealed high dioxygen association rate constants and low activation enthalpies for myohemerythrin with rate-liming diffusion of dioxygen through the protein matrixes; the dioxygen dissociation rates have much higher activation enthalpies than those of association, suggesting rate-determining bond breakage and/or substantial rearrangement of the metal coordination spheres (5). The four major alpha-helices occur between, Glu-19 and Arg-37, Ala-41 and Ala-64, Val-70 and Gly-85, and Ala-93 and Gly-109. <>/ProcSet[/PDF/Text/ImageB]/XObject<>>>/Type/Page>> endobj Without this moiety, myohemerythrin would not be able to bind oxygen reversibly and the coiled-coil motif would lose stability as the binuclear core binds all four helices. Despite its name Hr contains no heme group but rather a nonheme diiron site that reversibly binds one molecule of O2. Über die Blutzellen von, Stenkamp RE, Sieker LC, Jensen LH (1978) Crystallographic studies of azide, thiocyanate and perchlorate complexes of methemerythrin. Hemerythrin exists physiologically as a homooctamer of a 113 amino acid residue monomer; the octamer contains 8 oxo-/hydroxo-diiron cores each with the ability to reversibly bind dioxygen. Natl Acad Sci Lett (India) 4: 41–43, Mangum CP, Burnett LE (1987) Response of sipunculid hemerythrins to inorganic ions and CO. Mangum CP, Kondon M (1975) The role of coelomic hemerythrin in the sipunculid worm, Manwell C (1960a) Histological specificity of respiratory pigments II. The smaller the E Value, the more significant the alignment (14). Studies measuring dioxygen affinities and association and dissociation rates constants have revealed high dioxygen association rate constants and low activation enthalpies for myohemerythrin with rate-liming diffusion of dioxygen through the protein matrixes; the dioxygen dissociation rates have much higher activation enthalpies than those of association, suggesting rate-determining bond breakage and/or substantial rearrangement of the metal coordination spheres (5).