Sandbox Reserved 640: Difference between revisions

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The 16 kDa polypeptide leghemoglobin consists of two main subunits, the main globin structure and the iron-encompassing heme (protoporphyrin XI) group. These two subunits form a molecule structurally similar to Myoglobin <ref name=a />. The globin fold portion of the molecule is the standard globin secondary structure, a series of <scene name='Sandbox_Reserved_640/Alpha_helices/1'>8 alpha helices</scene> <ref name=five />. Depending on the species and specific type of Leghemoglobin, the primary amino acid sequence can differ some, but overall it is well conserved.

The <scene name='Sandbox_Reserved_640/Heme/1'>heme</scene> prosthetic group consists of four 5-membered pyrrole rings, forming a cyclic ring around a central iron (Fe) atom. This atom is contained within four equatorial nitrogens, in addition to another nitrogen from a close histidine residue and an opposite dioxygen (Ref 9). The ligand contact residues along the heme group are Phe30, <scene name='Sandbox_Reserved_640/His63/1'>His63</scene>, and Val67. Depending on the specific type of Leghemoglobin, some of these specific residues are disordered and others interconvert between two conformations (~~Ref 7~~).

The <scene name='Sandbox_Reserved_640/Heme/1'>heme</scene> prosthetic group consists of four 5-membered pyrrole rings, forming a cyclic ring around a central iron (Fe) atom. This atom is contained within four equatorial nitrogens, in addition to another nitrogen from a close histidine residue and an opposite dioxygen (Ref 9). The ligand contact residues along the heme group are Phe30, <scene name='Sandbox_Reserved_640/His63/1'>His63</scene>, and Val67. Depending on the specific type of Leghemoglobin, some of these specific residues are disordered and others interconvert between two conformations <ref name=seven>Narula, Surinder S., Claudio Dalvit, Cyril A. Appleby, and Peter E. Wright. "NMR Studies of the Conformations of Leghemoglobins from Soybean and Lupin." European Journal of Biochemistry 178.2 (1988): 419-35. Print.</ref>.

In opposition to the differences in polypeptides among globin proteins (Hemoglobin and Myoglobin), the heme group has been found to remain largely the same<ref name=a />. The main difference is a considerably larger heme group in Leghemoglobin than its other oxygen-transferring counterparts. The way the heme group attaches to the polypeptide is also different. The steric crowding around the ligand binding site (beside the heme) is reduced, plus there is an altered packing at the proximal side of the heme and conformational differences along the distal side. As a result, the oxygen affinity is larger than that of Myoglobin and Hemoglobin (Ref 8). This is reflected by the Km of 0.01 microM (the concentration for half of the Leghemoglobin to be saturated with dioxygen), about ten times the Michaelis constant for Hemoglobin ~~(Ref 7~~).

In opposition to the differences in polypeptides among globin proteins (Hemoglobin and Myoglobin), the heme group has been found to remain largely the same<ref name=a />. The main difference is a considerably larger heme group in Leghemoglobin than its other oxygen-transferring counterparts. The way the heme group attaches to the polypeptide is also different. The steric crowding around the ligand binding site (beside the heme) is reduced, plus there is an altered packing at the proximal side of the heme and conformational differences along the distal side. As a result, the oxygen affinity is larger than that of Myoglobin and Hemoglobin (Ref 8). This is reflected by the Km of 0.01 microM (the concentration for half of the Leghemoglobin to be saturated with dioxygen), about ten times the Michaelis constant for Hemoglobin <ref name=seven />).

The methods by which various Leghemoglobins were purified, and then analyzed, are as follows:

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 The 16 kDa polypeptide leghemoglobin consists of two main subunits, the main globin structure and the iron-encompassing heme (protoporphyrin XI) group.  These two subunits form a molecule structurally similar to Myoglobin <ref name=a />.  The globin fold portion of the molecule is the standard globin secondary structure, a series of <scene name='Sandbox_Reserved_640/Alpha_helices/1'>8 alpha helices</scene> <ref name=five />.  Depending on the species and specific type of Leghemoglobin, the primary amino acid sequence can differ some, but overall it is well conserved.
-The <scene name='Sandbox_Reserved_640/Heme/1'>heme</scene> prosthetic group consists of four 5-membered pyrrole rings, forming a cyclic ring around a central iron (Fe) atom.  This atom is contained within four equatorial nitrogens, in addition to another nitrogen from a close histidine residue and an opposite dioxygen (Ref 9).  The ligand contact residues along the heme group are Phe30, <scene name='Sandbox_Reserved_640/His63/1'>His63</scene>, and Val67.  Depending on the specific type of Leghemoglobin, some of these specific residues are disordered and others interconvert between two conformations (Ref 7).
+The <scene name='Sandbox_Reserved_640/Heme/1'>heme</scene> prosthetic group consists of four 5-membered pyrrole rings, forming a cyclic ring around a central iron (Fe) atom.  This atom is contained within four equatorial nitrogens, in addition to another nitrogen from a close histidine residue and an opposite dioxygen (Ref 9).  The ligand contact residues along the heme group are Phe30, <scene name='Sandbox_Reserved_640/His63/1'>His63</scene>, and Val67.  Depending on the specific type of Leghemoglobin, some of these specific residues are disordered and others interconvert between two conformations <ref name=seven>Narula, Surinder S., Claudio Dalvit, Cyril A. Appleby, and Peter E. Wright. "NMR Studies of the Conformations of Leghemoglobins from Soybean and Lupin." European Journal of Biochemistry 178.2 (1988): 419-35. Print.</ref>.
-In opposition to the differences in polypeptides among globin proteins (Hemoglobin and Myoglobin), the heme group has been found to remain largely the same<ref name=a />.  The main difference is a considerably larger heme group in Leghemoglobin than its other oxygen-transferring counterparts.  The way the heme group attaches to the polypeptide is also different.  The steric crowding around the ligand binding site (beside the heme) is reduced, plus there is an altered packing at the proximal side of the heme and conformational differences along the distal side.  As a result, the oxygen affinity is larger than that of Myoglobin and Hemoglobin (Ref 8).  This is reflected by the Km of 0.01 microM (the concentration for half of the Leghemoglobin to be saturated with dioxygen), about ten times the Michaelis constant for Hemoglobin (Ref 7).
+In opposition to the differences in polypeptides among globin proteins (Hemoglobin and Myoglobin), the heme group has been found to remain largely the same<ref name=a />.  The main difference is a considerably larger heme group in Leghemoglobin than its other oxygen-transferring counterparts.  The way the heme group attaches to the polypeptide is also different.  The steric crowding around the ligand binding site (beside the heme) is reduced, plus there is an altered packing at the proximal side of the heme and conformational differences along the distal side.  As a result, the oxygen affinity is larger than that of Myoglobin and Hemoglobin (Ref 8).  This is reflected by the Km of 0.01 microM (the concentration for half of the Leghemoglobin to be saturated with dioxygen), about ten times the Michaelis constant for Hemoglobin <ref name=seven />).
 The methods by which various Leghemoglobins were purified, and then analyzed, are as follows: