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Hemoglobin: Difference between revisions

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<StructureSection load='1gzx' size='350' side='right' caption="Human Hemoglobin α chain (grey and pink) β chain (green and yellow) with bound O2 [[1gzx]]" scene="Hemoglobin/Foursubunits/5" >
<StructureSection load='1gzx' size='350' side='right' caption="Human Hemoglobin α chain (grey and pink) β chain (green and yellow) with bound O2 [[1gzx]]" scene="Hemoglobin/Foursubunits/5" >
== Function ==
== Function ==
'''Hemoglobin''' is an oxygen-transport protein.  Hemoglobin is an allosteric protein.  It is a <scene name='32/32/Subunits_1hho/1'>tetramer</scene> composed of two types of subunits designated α and β, with stoichiometry <scene name='Hemoglobin/Alpha2beta2/7'>α2β2</scene>. The  <scene name='Hemoglobin/Foursubunits/5'>four subunits</scene> of hemoglobin sit roughly at the corners of a tetrahedron, facing each other across a <scene name='Hemoglobin/Cavity/9'>cavity</scene> at the center of the molecule. Each of the subunits <scene name='Hemoglobin/Bbsubunitswithheme/5'>contains a heme</scene> prosthetic group. The <scene name='Hemoglobin/4heme/3'>heme molecules</scene> give hemoglobin its red color.
'''Hemoglobin''' is an oxygen-transport protein.  Hemoglobin is an allosteric protein.  It is a <jmol>
  <jmolLink>
    <script> script /scripts/32/32/Subunits_1hho/1.spt;
            center visible;</script>
    <text>tetramer</text>
  </jmolLink>
</jmol> composed of two types of subunits designated α and β, with stoichiometry <scene name='Hemoglobin/Alpha2beta2/7'>α2β2</scene>. The  <scene name='Hemoglobin/Foursubunits/5'>four subunits</scene> of hemoglobin sit roughly at the corners of a tetrahedron, facing each other across a <scene name='Hemoglobin/Cavity/9'>cavity</scene> at the center of the molecule. Each of the subunits <scene name='Hemoglobin/Bbsubunitswithheme/5'>contains a heme</scene> prosthetic group. The <scene name='Hemoglobin/4heme/3'>heme molecules</scene> give hemoglobin its red color.


Each individual <scene name='Hemoglobin/Deoxyheme/8'>heme</scene> molecule contains one <scene name='Hemoglobin/Deoxyheme_fe/9'>Fe2+</scene> atom. In the lungs, where oxygen is abundant, an <scene name='Hemoglobin/Oxyheme_fe/7'>oxygen molecule</scene> binds to the ferrous iron atom of the heme molecule and is later released in tissues needing oxygen. The heme group binds oxygen while still attached to the <scene name='Hemoglobin/Oxysubunit/8'>hemoglobin monomer</scene>. The spacefill view of the hemoglobin polypeptide subunit with an oxygenated heme group shows how the <scene name='Hemoglobin/Oxysubunitsf/4'>oxygenated heme group is held</scene> within the polypeptide.  
Each individual <scene name='Hemoglobin/Deoxyheme/8'>heme</scene> molecule contains one <scene name='Hemoglobin/Deoxyheme_fe/9'>Fe2+</scene> atom. In the lungs, where oxygen is abundant, an <scene name='Hemoglobin/Oxyheme_fe/7'>oxygen molecule</scene> binds to the ferrous iron atom of the heme molecule and is later released in tissues needing oxygen. The heme group binds oxygen while still attached to the <scene name='Hemoglobin/Oxysubunit/8'>hemoglobin monomer</scene>. The spacefill view of the hemoglobin polypeptide subunit with an oxygenated heme group shows how the <scene name='Hemoglobin/Oxysubunitsf/4'>oxygenated heme group is held</scene> within the polypeptide.  
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Perhaps the most well-known disease caused by a mutation in the hemoglobin protein is sickle-cell anemia.  It results from a mutation of the sixth residue in the β hemoglobin monomer from <scene name='32/32/Hemoglobins_1hho/9'>glutamic acid to a valine</scene>.  This hemoglobin variant is termed 'hemoglobin S' ([[2hbs]]).
Perhaps the most well-known disease caused by a mutation in the hemoglobin protein is sickle-cell anemia.  It results from a mutation of the sixth residue in the β hemoglobin monomer from <scene name='32/32/Hemoglobins_1hho/9'>glutamic acid to a valine</scene>.  This hemoglobin variant is termed 'hemoglobin S' ([[2hbs]]).
*'''mini hemoglobin''' found in neural tissue and contains 109 residues<ref>PMID:9642264</ref> .
*'''mini hemoglobin''' found in neural tissue and contains 109 residues<ref>PMID:9642264</ref> .
*'''giant hemoglobin''' are sulfur-binding 400kDa hemoglobin found in mouthless and gutless marine animals which get their nutrition by symbiosis with sulfur-oxidizing bacteria<ref>PMID:16204001</ref> .
*'''truncated hemoglobin''' found in bacteria and plants.  They are 20-40 residues shorter than other Hb and have 2-on-2 alpha helical sandwich structure vs the 3-on-3 of other Hbs<ref>PMID:11696555</ref> .
*'''methemoglobin''' contains Fe+3 rather than Fe+2 can cause the lethal disease methemoglobinemia<ref>PMID:30726002</ref> .
*'''leghemoglobin''' found in roots of legumes<ref>PMID:29642729</ref> .
*'''flavohemoglobin''' is flavin-binding.  It binds NO and acts in its catabolism<ref>PMID:18379989</ref> .


==Hemoglobin subunit binding O<sub>2</sub>==
==Hemoglobin subunit binding O<sub>2</sub>==
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*Squires, J.E. (2002) Artificial Blood, Science 295, 1002.
*Squires, J.E. (2002) Artificial Blood, Science 295, 1002.
*Vichinsky, E. (2002) New therapies in sickle cell disease. Lancet 24, 629.
*Vichinsky, E. (2002) New therapies in sickle cell disease. Lancet 24, 629.
<references/>


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