Hemerythrin: Alternative Oxygen Carrier

Klotz, Irving M.; Klippenstein, Gerald L.; Hendrickson, Wayne A.

doi:10.1126/science.1257769

Cited by 80 publications

(32 citation statements)

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“…These findings were made yet more interesting when amino acid sequence data became available for the tyrosine-sensitive enzyme, and it was found that there was some similarity between the sequence of residues 10 through 18 of this DAHP synthase and that of residues 54 through 62 of several hemerythrins (7). Hemerythrin is the iron-containing oxygen carrier of sea worms (10) and has an absorption band around 350 nm. This spectroscopic parallel coupled with the sequence similarity suggested the existence of an iron-binding site in DAHP synthase that is analogous to that in hemerythrin (7).…”

mentioning

confidence: 99%

Is the first enzyme of the shikimate pathway, 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase (tyrosine sensitive), a copper metalloenzyme?

Baasov

Knowles

1989

J Bacteriol

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3-Deoxy-D-arabino-heptulosonate-7-phosphate synthase (tyrosine sensitive) was purified from Escherichia coli carrying the plasmid pKB45. Enzyme of high specific catalytic activity (70 IL/mg) was obtained from cells grown only to the early log phase. The purified protein contained Cu(ll) and showed an absorption band at 350 nm. Metal-free, catalytically inactive apoenzyme could be produced by dialysis against cyanide ion, and the holoenzyme could be reconstituted in terms of both catalytic activity and A350 by the binding of one Cu(II) ion per enzyme subunit. Zn(ll) also reactivated the apoenzyme to about 50% of the level seen with Cu(ll), although in this case no band appeared at 350 nm. In contrast to earlier reports that the enzyme contains substoichiometric levels of iron, insignificant amounts of iron were found in the isolated enzyme, and neither Fe(II) nor FE(Ill) regenerated either an absorption band at 350 nm or any catalytic activity from the apoenzyme. The evident preference of the enzyme as isolated for (Cu)II suggests that the synthase might naturally be a copper metalloenzyme.The first step of the shikimate pathway involves the condensation of phosphoenolpyruvate and erythrose 4-phosphate to produce the seven carbon keto acid, 3-deoxy-D-arabino-heptulosonate 7-phosphate (DAHP; Fig. 1). This reaction is catalyzed by DAHP synthase (EC 4.1.2.15), three isozyme forms of which exist in most microorganisms. Each isozyme is sensitive to feedback inhibition by one of the three aromatic amino acid products of the shikimate pathway (phenylalanine, tyrosine, or tryptophan), and this sensitivity is believed to represent an important element in the regulation of the metabolic sequence (6,20).One or more isozymes have been isolated from several sources, including Escherichia coli, Salmonella typhimurium, Bacillus subtilis, and Schizosaccharomyces pombe, but there is no real consensus on the properties even of the same isozyme from the same organism. For example, the activity of the tyrosine-sensitive enzyme from S. typhimurium has been found to depend upon the presence of Co(II) (14) and, later, to be independent of Co(II) and unaffected by the metal chelator EDTA (3). Similarly, the tyrosine-sensitive enzyme from E. coli has been found to be insensitive to Co(II) and to EDTA (18), whereas other reports suggest the opposite (4). The question of the metal requirement of DAHP synthase then appeared to have been resolved by the findings of Herrmann et al., who reported that both the phenylalanine-sensitive and the tyrosine-sensitive enzymes contain iron rather than cobalt (12). The bound iron appeared to be essential for the catalytic activity and, in the presence of one of the substrates (phosphoenolpyruvate), gave rise to an absorption band at 350 nm (12). These findings were made yet more interesting when amino acid sequence data became available for the tyrosine-sensitive enzyme, and it was found that there was some similarity between the sequence of residues 10 through 18 of this DAHP synthase and that of resid...

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mentioning

confidence: 99%

Is the first enzyme of the shikimate pathway, 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase (tyrosine sensitive), a copper metalloenzyme?

Baasov

Knowles

1989

J Bacteriol

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“…A smaller molecule, myohemerythrin, related to the subunit of hemerythrin, is found in the muscle tissue of organisms containing the octamer, analogous to the hemoglobin-myoglobin system found in most other organisms. Extensive discussions of the biochemistry of these molecules can be found in review articles by Klotz (1971), Llinas (1973), and Klotz, Klippenstein & Hendrickson (1976).…”

Section: Introductionmentioning

confidence: 99%

Difference Fourier refinement of metaquohemerythrin

Stenkamp¹,

Sieker²,

Jensen³

1978

Acta Cryst Sect A

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A model for metaquohemerythrin from Themiste dyscritum has been refined in the crystallographic sense of the term by difference Fourier methods at 2.8 and 2.5 ,/~ resolution. Fourteen cycles of refinement reduced R from an initial value of 0.385 for the 9461 reflections from I0 to 2.8/k to 0.253 for 16 363 reflections from 10 to 2-5 A resolution. On the basis of peaks in difference maps, 49 water molecules have been added to the model for a total of 3833 atoms in the asymmetric unit.

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“…(2,4) and from the Pacific Coast sipunculid, Themiste dyscritum (T. dyscritum) (5,6). Upon solving the crystal structure of T. dyscrituni hemerythrin, two.mercu~y binding sites were observed in the heavy atom deriva~ive prepared by treat~ng the protein with_ mercuric iodide.…”

mentioning

confidence: 99%

“…The titration data showed that 1.5 atoms of mercury were bound per subunit, which 2 is consistent with one mercury bound at cysteine 50 and one mercury shared by cysteine 9's of a~jacent subunits. The mercuric iodide binding at cysteine 50 appears to be a lin~ar structure (Protein-S-Hg-I), while the·mercury bridging two cysteine 9's on adjacent subunits is better explained by a tetrahedral structure [(Protein-s) 2 HgI 2 ].…”

mentioning

confidence: 99%

“…One mercury is' near the cysteine 50 residue of each subunit while the other mercury appears to be bridging cysteine 9 residues of adjacent subunits. 2 This study was undertaken to determine whether the mercury in the heavy atom derivative of T. dyscritum hemerythrin was, in fact, covalently bound to cysteine sulfur atoms and, if so, to elucidate the structure of the mercury-sulfur complexes in the protein. It, was also of interest to understand how mercuric iodide was able to bind to T. dyscritum hemerythr_in without causing it ·to dissociate into subunits, since many sulfhydryl-specif ic reagents are known to cause disruption of the octameric structure of P. gouldii hemerythrin (3).…”

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Involvement of Hemerythrin Sulfhydryl Groups in Heavy Atom Binding and Subunit Interactions

Clarke

2000

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Hemerythrin is a respiratory protein found in the erythrocytes of certain marine invertebrates. Structures have.been obtained by x~ray c~ystallography for hemerythrins from Phascolopsis gouldii (P. gouldii) and:Themiste·dyscritum (!. dyscritum). Upon solving the crystal structure of T. dyscritum hemerythrin at 2.8 A resolution, two mercury binding sites were observed in the heavy atom derivative prepared by treating the protein with mercuric iodide. Since many proteins are inactivated upon binding heavy metals such as mercury, an investigation of mercury-protein interactions in this protein was undertaken. In order to understand the nature of heavy-metal protein interactions in T. dyscritum it was necessary to identify the metalloprotein ligands since neither the liga~ding ami~o acid residues nor the geometry of the mercury complexes could be identified in the crystallographic studies. · Once the amino acid sequence of_ T. dyscritum hemerythrin was determined, it was clear that both mercury binding si~es were close to the thiol groups of two cysteine residues (cysteine 9 and cysteine 50). Possible struc~ures for the mercury binding sites were identified by combining a ;knowledge of hemerythrin structure with direct evidence for mercury-thiol bond formation obtained by spectrophotometric titration of the thiol groups with mercuric iodide. The titration data showed that 1.5 atoms of mercury were bound per subunit, which 2 is consistent with one mercury bound at cysteine 50 and one mercury shared by cysteine 9's of a~jacent subunits. The mercuric iodide binding at cysteine 50 appears to be a lin~ar structure (Protein-S-Hg-I), while the·mercury bridging two cysteine 9's on adjacent subunits is better explained by a tetrahedral structure [(Protein-s) 2HgI 2 ].The relative reaction rates of the .thiol groups in hemerythrin with p-hydroxymercuribenzoate (PHMB) and N-ethylmaleimide (NEM) were investigat.ed· in order to gain information about the comparative hydrophobicity. of the environm~nts surrounding the t~o cysteines. The data showed the environment about cysteine 50 to. be hydrophobic relative to the environment about cysteine 9. This was substantiated by structural information whtch showed cysteine 50 to be buried in a subunit interface while.cysteine 9 was in a region relatively exposed 3 to the solvent.

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Hemerythrin: Alternative Oxygen Carrier

Cited by 80 publications

References 50 publications

Is the first enzyme of the shikimate pathway, 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase (tyrosine sensitive), a copper metalloenzyme?

Is the first enzyme of the shikimate pathway, 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase (tyrosine sensitive), a copper metalloenzyme?

Difference Fourier refinement of metaquohemerythrin

Involvement of Hemerythrin Sulfhydryl Groups in Heavy Atom Binding and Subunit Interactions

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