UMMS Affiliation

Department of Cell and Developmental Biology

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Document Type



Chlamydomonas reinhardtii; Chloroplast Proteins; Gene Expression Regulation, Plant; Heme; Hemoglobins; Hydrogen-Ion Concentration; Lysine; Nitric Oxide; Nitrogen




The nuclear genome of the model organism Chlamydomonas reinhardtii contains genes for a dozen hemoglobins of the truncated lineage. Of those, THB1 is known to be expressed, but the product and its function have not yet been characterized. We present mutagenesis, optical, and nuclear magnetic resonance data for the recombinant protein and show that at pH near neutral in the absence of added ligand, THB1 coordinates the heme iron with the canonical proximal histidine and a distal lysine. In the cyanomet state, THB1 is structurally similar to other known truncated hemoglobins, particularly the heme domain of Chlamydomonas eugametos LI637, a light-induced chloroplastic hemoglobin. Recombinant THB1 is capable of binding nitric oxide (NO(*)) in either the ferric or ferrous state and has efficient NO(*) dioxygenase activity. By using different C. reinhardtii strains and growth conditions, we demonstrate that the expression of THB1 is under the control of the NIT2 regulatory gene and that the hemoglobin is linked to the nitrogen assimilation pathway.

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Open access via the ACS AuthorChoice + 12, Open Access option on 06/25/2015.

DOI of Published Version



Biochemistry. 2014 Jul 22;53(28):4573-89. doi: 10.1021/bi5005206. Link to article on publisher's site.

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Link to Article in PubMed

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Biochemistry Commons



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