A hemoglobin from plants homologous to truncated hemoglobins of microorganisms

Watts, Richard A.; Hunt, Peter W.; Hvitved, Angela N.; Hargrove, Mark S.; Peacock, W. J.; Dennis, Elizabeth S.

doi:10.1073/pnas.191349198

Cited by 186 publications

(177 citation statements)

References 30 publications

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“…Alternatively, the multiple hexacoordinated states may account for multiple functions in the same molecule. Hexacoordinated Hbs are observed in unicellular eukaryotes [17], plants [49], invertebrates [50], and in some tissues of higher vertebrates [48,51], but only a few cases have been examined and reported in the literature for bacterial 2/2 Hbs [52][53][54][55]. The physiological role of these hexacoordinated Hbs is not well understood.…”

Section: Discussionmentioning

confidence: 99%

The peculiar heme pocket of the 2/2 hemoglobin of cold-adapted Pseudoalteromonas haloplanktis TAC125

et al. 2010

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The genome of the cold-adapted bacterium Pseudoalteromonas haloplanktis TAC125 contains multiple genes encoding three distinct monomeric hemoglobins exhibiting a 2/2 a-helical fold. In the present work, one of these hemoglobins is studied by resonance Raman, electronic absorption and electronic paramagnetic resonance spectroscopies, kinetic measurements, and different bioinformatic approaches. It is the first cold-adapted bacterial hemoglobin to be characterized. The results indicate that this protein belongs to the 2/2 hemoglobin family, Group II, characterized by the presence of a tryptophanyl residue on the bottom of the heme distal pocket in position G8 and two tyrosyl residues (TyrCD1 and TyrB10). However, unlike other bacterial hemoglobins, the ferric state, in addition to the aquo hexacoordinated high-spin form, shows multiple hexacoordinated low-spin forms, where either TyrCD1 or TyrB10 can likely coordinate the iron. This is the first example in which both TyrCD1 and TyrB10 are proposed to be the residues that are alternatively involved in heme hexacoordination by endogenous ligands.

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Section: Discussionmentioning

confidence: 99%

The peculiar heme pocket of the 2/2 hemoglobin of cold-adapted Pseudoalteromonas haloplanktis TAC125

et al. 2010

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“…The absorption spectra of an A. thaliana tHb showed that Fe-heme from this protein is pentacoordinate 82, 91 . Thus, it is likely that Fe-heme in rice tHb is pentacoordinate and that the O 2 -binding properties of rice tHb are similar to those of pentacoordante Hbs, i.e .…”

Section: Structure and Biophysical Properties Of Rice Hemoglobinsmentioning

confidence: 97%

“…It is well documented that land plant hb genes are either up- or down-regulated by stress conditions 1, 52, 54, 79– 82 . Table 1 shows that Hb transcripts coexist in rice growing under cold, drought and salt stress conditions.…”

Section: Molecular Biology Of Rice Hemoglobinsmentioning

confidence: 99%

Rice (Oryza) hemoglobins

2014

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Hemoglobins (Hbs) corresponding to non-symbiotic (nsHb) and truncated (tHb) Hbs have been identified in rice ( Oryza). This review discusses the major findings from the current studies on rice Hbs. At the molecular level, a family of the nshb genes, consisting of hb1, hb2, hb3, hb4 and hb5, and a single copy of the thb gene exist in Oryza sativa var. indica and O. sativa var. japonica, Hb transcripts coexist in rice organs and Hb polypeptides exist in rice embryonic and vegetative organs and in the cytoplasm of differentiating cells. At the structural level, the crystal structure of rice Hb1 has been elucidated, and the structures of the other rice Hbs have been modeled. Kinetic analysis indicated that rice Hb1 and 2, and possibly rice Hb3 and 4, exhibit an extremely high affinity for O 2, whereas rice Hb5 and tHb possibly exhibit a low to moderate affinity for O 2. Based on the accumulated information on the properties of rice Hbs and data from the analysis of other plant and non-plant Hbs, it is likely that Hbs play a variety of roles in rice organs, including O 2-transport, O 2-sensing, NO-scavenging and redox-signaling. From an evolutionary perspective, an outline for the evolution of rice Hbs is available. Rice nshb and thb genes vertically evolved through different lineages, rice nsHbs evolved into clade I and clade II lineages and rice nshbs and thbs evolved under the effect of neutral selection. This review also reveals lacunae in our ability to completely understand rice Hbs. Primary lacunae are the absence of experimental information about the precise functions of rice Hbs, the properties of modeled rice Hbs and the cis-elements and trans-acting factors that regulate the expression of rice hb genes, and the partial understanding of the evolution of rice Hbs.

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“…Truncated hemoglobins (trHbs) are small heme proteins found in bacteria, unicellular eukaryotes, and higher plants forming a group within the hemoglobin superfamily (1). TrHbs have less than 15% sequence identity when compared with vertebrate and nonvertebrate hemoglobins (2,3).…”

Section: Introductionmentioning

confidence: 99%

Ligand migration in the truncated hemoglobin of Mycobacterium tuberculosis

2011

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SummaryThe truncated hemoglobin of Mycobacterium tuberculosis (Mt-trHbO) is a small heme protein belonging to the hemoglobin superfamily. Truncated hemoglobins (trHbs) are believed to have functional roles such as terminal oxidases and oxygen sensors involved in the response to oxidative and nitrosative stress, nitric oxide (NO) detoxification, O 2 /NO chemistry, O 2 delivery under hypoxic conditions, and long-term ligand storage. Based on sequence similarities, they are classified into three groups. Experimental studies revealed that all trHbs display a 2-on-2 ahelical sandwich fold rather than the 3-on-3 a-helical sandwich fold of the classical hemoglobin fold. Using locally enhanced sampling (LESMD) molecular dynamics, the ligand-binding escape pathways from the distal heme binding cavity of MttrHbO were determined to better understand how this protein functions. The importance of specific residues, such as the group II and III invariant W(G8) residue, can be seen in terms of ligand diffusion pathways and ligand dynamics. LESMD simulations show that the wild-type Mt-trHbO has three diffusion pathways while the W(G8)F Mt-trHbO mutant has only two. The W(G8) residue plays a critical role in ligand binding and stabilization and helps regulate the rate of ligand escape from the distal heme pocket. Thus, this invariant residue is important in creating ligand diffusion pathways and possibly in the enzymatic functions of this protein.

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A hemoglobin from plants homologous to truncated hemoglobins of microorganisms

Cited by 186 publications

References 30 publications

The peculiar heme pocket of the 2/2 hemoglobin of cold-adapted Pseudoalteromonas haloplanktis TAC125

The peculiar heme pocket of the 2/2 hemoglobin of cold-adapted Pseudoalteromonas haloplanktis TAC125

Rice (Oryza) hemoglobins

Ligand migration in the truncated hemoglobin of Mycobacterium tuberculosis

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