NDLI: A TyrCD1/TrpG8 hydrogen bond network and a TyrB10—TyrCD1 covalent link shape the heme distal site of Mycobacterium tuberculosis hemoglobin O

Content Provider	PubMed Central
Author	Milani, Mario Savard, Pierre-yves Ouellet, Hugues Ascenzi, Paolo Guertin, Michel Bolognesi, Martino
Copyright Year	2003
Abstract	Truncated hemoglobins (Hbs) are small hemoproteins, identified in microorganisms and in some plants, forming a separate cluster within the Hb superfamily. Two distantly related truncated Hbs, trHbN and trHbO, are expressed at different developmental stages in Mycobacterium tuberculosis. Sequence analysis shows that the two proteins share 18% amino acid identities and belong to different groups within the truncated Hb cluster. Although a specific defense role against nitrosative stress has been ascribed to trHbN (expressed during the Mycobacterium stationary phase), no clear functions have been recognized for trHbO, which is expressed throughout the Mycobacterium growth phase. The 2.1-Å crystal structure of M. tuberculosis cyano-met trHbO shows that the protein assembles in a compact dodecamer. Six of the dodecamer subunits are characterized by a double conformation for their CD regions and, most notably, by a covalent bond linking the phenolic O atom of TyrB10 to the aromatic ring of TyrCD1, in the heme distal cavity. All 12 subunits display a cyanide ion bound to the heme Fe atom, stabilized by a tight hydrogen-bonded network based on the (globin very rare) TyrCD1 and TrpG8 residues. The small apolar AlaE7 residue leaves room for ligand access to the heme distal site through the conventional “E7 path,” as proposed for myoglobin. Different from trHbN, where a 20-Å protein matrix tunnel is held to sustain ligand diffusion to an otherwise inaccessible heme distal site, the topologically related region in trHbO hosts two protein matrix cavities.
Related Links	http://dx.doi.org/10.1073/pnas.1037676100
Ending Page	5771
Page Count	6
Starting Page	5766
File Format	PDF
ISSN	00278424
e-ISSN	10916490
Journal	Proceedings of the National Academy of Sciences of the United States of America
Issue Number	10
Volume Number	100
Language	English
Publisher	The National Academy of Sciences
Publisher Date	2003-05-13
Access Restriction	Open
Rights Holder	The National Academy of Sciences
Subject Keyword	General Research in Higher Education
Content Type	Text
Resource Type	Article
Subject	Multidisciplinary

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