Myoglobin in a Cyanobacterium

Potts, Malcolm; Angeloni, Stephen V.; Ebel, Richard E.; Bassam, Deeni

doi:10.1126/science.256.5064.1690

Cited by 122 publications

(81 citation statements)

References 14 publications

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“…Hemoglobins have been discovered in many unicellular organisms in the recent past, but their physiological role is controversial (6). The putative hemoglobins from M. tuberculosis are similar to those found in ciliated protozoa (7,8), the cyanobacteria Nostoc commune (9) and Synechocystis (10), and the green alga Chlamydomonas eugametos (11). This family of hemoglobins is distinct from that comprising the dimeric hemoglobin of the bacterium Vitreoscilla stercoraria and the flavohemoglobins of bacteria and yeasts (12).…”

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confidence: 66%

A cooperative oxygen-binding hemoglobin from Mycobacterium tuberculosis

Couture

Yeh

Wittenberg

et al. 1999

Proc. Natl. Acad. Sci. U.S.A.

202

257

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Two putative hemoglobin genes, glbN and glbO, were recently discovered in the complete genome sequence of Mycobacterium tuberculosis H37Rv. Here, we show that the glbN gene encodes a dimeric hemoglobin (HbN) that binds oxygen cooperatively with very high affinity (P 50 ‫؍‬ 0.013 mmHg at 20°C) because of a fast combination (25 M ؊1 ⅐s ؊1 ) and a slow dissociation (0.2 s ؊1 ) rate. Resonance Raman spectroscopy and ligand association͞dissociation kinetic measurements, along with mutagenesis studies, reveal that the stabilization of the bound oxygen is achieved through a tyrosine at the B10 position in the distal pocket of the heme with a conformation that is unique among the globins. Physiological studies performed with Mycobacterium bovis bacillus Calmette-Guérin demonstrate that the expression of HbN is greatly enhanced during the stationary phase in aerobic cultures but not under conditions of limited oxygen availability. The results suggest that, physiologically, the primary role of HbN may be to protect the bacilli against reactive nitrogen species produced by the host macrophage.

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mentioning

confidence: 66%

A cooperative oxygen-binding hemoglobin from Mycobacterium tuberculosis

Couture

Yeh

Wittenberg

et al. 1999

Proc. Natl. Acad. Sci. U.S.A.

202

257

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“…The cyanoglobin also binds oxygen reversibly with half-saturation oxygen tension (Ps,,) values of 0.32-0.99 mm Hg (Thorsteinsson et al, 1996). It is detected only under microaerobic conditions when the cells are starved of fixed nitrogen, suggesting that it could be involved in some aspect of nitrogen fixation (Potts et al, 1992). Interestingly, the gene encoding cyanoglobin (GIDN) is located between two genes that are essential for nitrogen fixation.…”

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confidence: 99%

Purification and Spectroscopic Characterization of a Recombinant Chloroplastic Hemoglobin from the Green Unicellular Alga Chlamydomonas eugametos

Couture

Guertin

1996

European Journal of Biochemistry

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Hemoglobins (Hb), which have the important task of delivering molecular oxygen by facilitating its reversible binding to the heme, are now thought to have evolved in all groups of organisms including prokaryotes, fungi, plants and animals. Our recent finding of a light-inducible chloroplastic Hb in the green unicellular alga Chlamydomonas eugametos has further extend this idea, while raising questions about the function that an Hb could play in a high oxygen environment such as in the chloroplast. In order to understand the role played by this new Hb, we have undertaken its biochemical characterization. To facilitate the characterization of Chlamydomonas Hb, which represents less than 0.01 % of the soluble protein in the green alga, the protein has been expressed in Escherichia coli and purified to apparent homogeneity. The purified recombinant protein possesses a non-covalently bound iron-protoporphyrin IX heme. The oxy form of the recombinant Hb, purified directly from bacterial cells, is very stable, with a measured half-life of 7 days at pH 8 and has an ultraviolet/visible spectrum similar to those of the related cytoplasmic Hbs of the ciliated protozoa Paramecium and Tetrahymena and of the cyanobacterium Nostoc commune. In contrast to what has been reported for oxymyoglobins and oxyhemoglobins, the dioxygen molecule bound to the LI637 Hb can be reduced by the electron-transfer mediator phenazine methosulfate in the presence of NADPH, indicating that the heme pocket of Chlamydomonas Hb may be more accessible to small molecules. With regard to this, we found that when the small reducing agent sodium dithionite is used to reduce the met form, it must be removed anaerobically from the Hb prior to oxygenation of the protein to stably produce the oxy form. Otherwise, the oxy form is obtained readily from the met form under an oxygenic atmosphere when ferredoxin and ferredoxin NADP + reductase are used to enzymically reduce the Hb. Finally, the spectra of the deoxy and met forms were unusual, the heme being partly low-spin at physiological pH. These results confirm the existence of a reversible oxygen-binding protein in the chloroplast of C. eugametos. The unusual spectral and biochemical properties of the protein may reflect a specialized function for this Hb.

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“…On the basis of sequence alignments, two groups of hemoglobins have been identified in unicellular organisms (4,(8)(9)(10)(11)(12). The first group consists of flavohemoglobins from bacteria and fungi (13)(14)(15)(16)(17).…”

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Unique Ligand−Protein Interactions in a New Truncated Hemoglobin from Mycobacterium tuberculosis

et al. 2002

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A new truncated hemoglobin (HbO) from Mycobacterium tuberculosis has been expressed and purified. Sequence alignment of HbO with other hemoglobins suggests that the proximal F8 residue is histidine and the distal E7 and the B10 positions are occupied by alanine and tyrosine, respectively. The highly conserved residue at the CD1 position, surprisingly, is tyrosine, making HbO the first exception in the hemoglobin family that does not contain phenylalanine at this position. Resonance Raman data suggest that a strong hydrogen bonding network, involving the B10 Tyr and the CD1 Tyr, stabilizes the heme-bound O 2 and CO as evidenced by the relatively low frequency of the Fe-O 2 stretching mode (559 cm -1 ) and the high frequency of the Fe-CO stretching mode (527 cm -1 ). The presence of this hydrogen bonding network is supported by mutagenesis studies with the B10 tyrosine or the CD1 tyrosine mutated to phenylalanine. Taken together, these data demonstrate a rigid and polar distal pocket in HbO, which is significantly different from that of HbN, the other hemoglobin from M. tuberculosis. The distinct features in the heme active site structures and the temporal expression patterns of HbO and HbN suggest that these two hemoglobins may have very different physiological functions.

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Myoglobin in a Cyanobacterium

Cited by 122 publications

References 14 publications

A cooperative oxygen-binding hemoglobin from Mycobacterium tuberculosis

A cooperative oxygen-binding hemoglobin from Mycobacterium tuberculosis

Purification and Spectroscopic Characterization of a Recombinant Chloroplastic Hemoglobin from the Green Unicellular Alga Chlamydomonas eugametos

Unique Ligand−Protein Interactions in a New Truncated Hemoglobin from Mycobacterium tuberculosis

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