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| ==Truncated hemoglobins== | | ==Truncated hemoglobins== |
| | | see [[Journal:JBIC:8]] |
| <!-- <StructureSection load='Jbic8.pdb' size='500' side='right' scene='Journal:JBIC:8/Cv/1' caption=''> -->
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| <scene name='Journal:JBIC:8/Trhb/1'>Truncated hemoglobins</scene>, also known as 2/2 hemoglobins, can be further classified into three different groups (I, II, and III). Genomic sequences of bacteria, cyanobacteria, and plants indicate that trHbs are rather common. Group I, Group II, and Group III trHbs have distinct phylogenetic trees and show different ligand-binding properties. The Group I trHb of the ciliated protozoan ''Tetrahymena pyriformis'' (''Tp'' trHb) was first discovered by Keilin and Ryley in 1953.
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| It is known that trHbs exist in ciliates of the Tetrahymena group, but trHb structure and function remain poorly understood. To investigate trHb function with respect to stability of bound oxygen and protein structure, we measured the oxygen binding kinetics of Tetrahymena pyriformis trHb, and determined the crystal structure of the protein.
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| The three-dimensional structure of an <scene name='Journal:JBIC:8/Trhb/2'>Fe(II)-O2 complex of Tp trHb</scene> was determined at 1.73 Å resolution ([[3aq9]]). <scene name='Journal:JBIC:8/Trhb/3'>Tyr25 (B10) and Gln46 (E7) were hydrogen-bonded to a heme-bound dioxygen molecule</scene>. Tyr25 donated a hydrogen bond to the terminal oxygen atom, whereas Gln46 hydrogen-bonded to the proximal oxygen atom. Furthermore, <scene name='Journal:JBIC:8/Trhb/4'>Tyr25 was hydrogen-bonded to the Gln46 and Gln50 (E11) residues</scene>.
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| The O<sub>2</sub> association and dissociation rate constants of ''T. pyriformis'' trHb were 5.5 μM<sup>-1</sup> s<sup>-1</sup>, and 0.18 s<sup>-1</sup>, respectively. The oxygen affinity was determined to be 33 nM. The autooxidation rate constant was 3.8 x 10<sup>-3</sup> h<sup>-1</sup>. These values are similar to those of <scene name='Journal:JBIC:8/Hbn/3'>HbN from Mycobacterium tuberculosis</scene>.
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| '''Mutations:'''
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| *Mutation at Tyr25: <scene name='43/435485/As/6'>Wildtype Y25 and mutant Y25F together</scene> and <scene name='43/435485/As/5'>animation of this scene</scene>. <jmol><jmolButton>
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| <script>if (_animating); anim pause;set echo bottom left; color echo white; font echo 20 sansserif;echo Animation Paused; else; anim resume; set echo off;endif;</script>
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| <text>Toggle Animation</text>
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| </jmolButton></jmol>
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| *Mutation at Gln46: <scene name='43/435485/Ad/4'>Wildtype Q46 and mutant Q46E together (animation)</scene> <jmol><jmolButton>
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| <script>if (_animating); anim pause;set echo bottom left; color echo white; font echo 20 sansserif;echo Animation Paused; else; anim resume; set echo off;endif;</script>
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| <text>Toggle Animation</text>
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| </jmolButton></jmol>
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| *Mutation at <scene name='Journal:JBIC:8/Trhb/11'>Gln50</scene> increased the O<sub>2</sub> dissociation and autooxidation rate constants, and partly disrupted the hydrogen-bonding network.
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| An <scene name='Journal:JBIC:8/Ag/4'>Fe(III)-H2O complex of Tp trHb was formed following reaction of the Fe(II)-O<sub>2</sub> complex of Tp trHb</scene>, in a crystal state, with nitric oxide. This suggests that ''Tp'' trHb functions in nitric oxide detoxification.
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| ==3D Printed Physical Model of Hemoglobin at The MSOE Center for BioMolecular Modeling== | | ==3D Printed Physical Model of Hemoglobin at The MSOE Center for BioMolecular Modeling== |
