2c0k: Difference between revisions

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==Overview==

Hemoglobins (Hbs) reversibly bind gaseous diatomic ligands (e.g., O2) as, the sixth heme axial ligand of the penta-coordinate deoxygenated form., Selected members of the Hb superfamily, however, display a functionally, relevant hexa-coordinate heme Fe atom in their deoxygenated state., Endogenous heme hexa-coordination is generally provided in these Hbs by, the E7 residue (often His), which thus modulates accessibility to the heme, distal pocket and reactivity of the heme toward exogenous ligands. Such a, pivotal role of the E7 residue is prominently shown by analysis of the, functional and structural properties of insect Hbs. Here, we report the, 2.6 A crystal structure of oxygenated Gasterophilus intestinalis Hb1, a Hb, known to display a penta-coordinate heme in the deoxygenated form. The, structure is analyzed in comparison with those of Drosophila melanogaster, Hb, exhibiting a hexa-coordinate heme in its deoxygenated derivative, and, of Chironomus thummi thummi HbIII, which displays a penta-coordinate heme, in the deoxygenated form. Despite evident structural differences in the, heme distal pockets, the distinct molecular mechanisms regulating O2, binding to the three insect Hbs result in similar O(2 affinities (P50, values ranging between 0.12 torr and 0.46 torr).

Hemoglobins (Hbs) reversibly bind gaseous diatomic ligands (e.g., O2) as the sixth heme axial ligand of the penta-coordinate deoxygenated form. Selected members of the Hb superfamily, however, display a functionally relevant hexa-coordinate heme Fe atom in their deoxygenated state. Endogenous heme hexa-coordination is generally provided in these Hbs by the E7 residue (often His), which thus modulates accessibility to the heme distal pocket and reactivity of the heme toward exogenous ligands. Such a pivotal role of the E7 residue is prominently shown by analysis of the functional and structural properties of insect Hbs. Here, we report the 2.6 A crystal structure of oxygenated Gasterophilus intestinalis Hb1, a Hb known to display a penta-coordinate heme in the deoxygenated form. The structure is analyzed in comparison with those of Drosophila melanogaster Hb, exhibiting a hexa-coordinate heme in its deoxygenated derivative, and of Chironomus thummi thummi HbIII, which displays a penta-coordinate heme in the deoxygenated form. Despite evident structural differences in the heme distal pockets, the distinct molecular mechanisms regulating O2 binding to the three insect Hbs result in similar O(2 affinities (P50 values ranging between 0.12 torr and 0.46 torr).

==About this Structure==

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[[Category: oxygen transport]]

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''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Thu Feb 21 16:43:36 2008''

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@@ Line 4: / Line 4: @@
 ==Overview==
-Hemoglobins (Hbs) reversibly bind gaseous diatomic ligands (e.g., O2) as, the sixth heme axial ligand of the penta-coordinate deoxygenated form., Selected members of the Hb superfamily, however, display a functionally, relevant hexa-coordinate heme Fe atom in their deoxygenated state., Endogenous heme hexa-coordination is generally provided in these Hbs by, the E7 residue (often His), which thus modulates accessibility to the heme, distal pocket and reactivity of the heme toward exogenous ligands. Such a, pivotal role of the E7 residue is prominently shown by analysis of the, functional and structural properties of insect Hbs. Here, we report the, 2.6 A crystal structure of oxygenated Gasterophilus intestinalis Hb1, a Hb, known to display a penta-coordinate heme in the deoxygenated form. The, structure is analyzed in comparison with those of Drosophila melanogaster, Hb, exhibiting a hexa-coordinate heme in its deoxygenated derivative, and, of Chironomus thummi thummi HbIII, which displays a penta-coordinate heme, in the deoxygenated form. Despite evident structural differences in the, heme distal pockets, the distinct molecular mechanisms regulating O2, binding to the three insect Hbs result in similar O(2 affinities (P50, values ranging between 0.12 torr and 0.46 torr).
+Hemoglobins (Hbs) reversibly bind gaseous diatomic ligands (e.g., O2) as the sixth heme axial ligand of the penta-coordinate deoxygenated form. Selected members of the Hb superfamily, however, display a functionally relevant hexa-coordinate heme Fe atom in their deoxygenated state. Endogenous heme hexa-coordination is generally provided in these Hbs by the E7 residue (often His), which thus modulates accessibility to the heme distal pocket and reactivity of the heme toward exogenous ligands. Such a pivotal role of the E7 residue is prominently shown by analysis of the functional and structural properties of insect Hbs. Here, we report the 2.6 A crystal structure of oxygenated Gasterophilus intestinalis Hb1, a Hb known to display a penta-coordinate heme in the deoxygenated form. The structure is analyzed in comparison with those of Drosophila melanogaster Hb, exhibiting a hexa-coordinate heme in its deoxygenated derivative, and of Chironomus thummi thummi HbIII, which displays a penta-coordinate heme in the deoxygenated form. Despite evident structural differences in the heme distal pockets, the distinct molecular mechanisms regulating O2 binding to the three insect Hbs result in similar O(2 affinities (P50 values ranging between 0.12 torr and 0.46 torr).
 ==About this Structure==
@@ Line 29: / Line 29: @@
 [[Category: oxygen transport]]
-''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Sun Feb  3 10:29:59 2008''
+''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Thu Feb 21 16:43:36 2008''