1uvx
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HEME-LIGAND TUNNELING ON GROUP I TRUNCATED HEMOGLOBINS
OverviewOverview
Truncated hemoglobins (trHbs) are small hemoproteins forming a separate, cluster within the hemoglobin superfamily; their functional roles in, bacteria, plants, and unicellular eukaryotes are marginally understood., Crystallographic investigations have shown that the trHb fold (a, two-on-two alpha-helical sandwich related to the globin fold) hosts a, protein matrix tunnel system offering a potential path for ligand, diffusion to the heme distal site. The tunnel topology is conserved in, group I trHbs, although with modulation of its size/structure. Here, we, present a crystallographic investigation on trHbs from Mycobacterium, tuberculosis, Chlamydomonas eugametos, and Paramecium caudatum, showing, that treatment of trHb crystals under xenon pressure leads to binding of, xenon atoms at specific (conserved) sites along the protein matrix tunnel., The crystallographic results are in keeping with data from molecular, dynamics simulations, where a dioxygen molecule is left free to diffuse, within the protein matrix. Modulation of xenon binding over four main, sites is related to the structural properties of the tunnel system in the, three trHbs and may be connected to their functional roles. In a parallel, crystallographic investigation on M. tuberculosis trHbN, we show that, butyl isocyanide also binds within the apolar tunnel, in excellent, agreement with concepts derived from the xenon binding experiments. These, results, together with recent data on atypical CO rebinding kinetics to, group I trHbs, underline the potential role of the tunnel system in, supporting diffusion, but also accumulation in multiple copies, of low, polarity ligands/molecules within group I trHbs.
About this StructureAbout this Structure
1UVX is a Single protein structure of sequence from Chlamydomonas eugametos with CYN, HEM and XE as ligands. Full crystallographic information is available from OCA.
ReferenceReference
Heme-ligand tunneling in group I truncated hemoglobins., Milani M, Pesce A, Ouellet Y, Dewilde S, Friedman J, Ascenzi P, Guertin M, Bolognesi M, J Biol Chem. 2004 May 14;279(20):21520-5. Epub 2004 Mar 11. PMID:15016811
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