Sandbox Reserved 640: Difference between revisions

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 1).  The globin fold portion of the molecule is the standard globin secondary structure, a series of 8 alpha helices (Ref 5).  Depending on the species and specific type of Leghemoglobin, the primary amino acid sequence can differ some, but overall it is well conserved.   

The heme prosthetic group has been found to be largely the same in different proteins and in different species (Ref 1).  The main difference is a considerably larger heme group in Leghemoglobin than its other oxygen-transferring globin counterparts.  The way the heme group attaches to the polypeptide is also different from myoglobin and hemoglobin.  The steric crowding around the ligand binding site (beside the heme) is less than the other proteins, plus the distal and proximal histidine residues are in different orientations (Ref 7).  This makes the oxygen affinity larger than that of Myoglobin and Hemoglobin (Ref 8).  This heme group, more specifically, 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 are Phe30, His63, His97, and Val67 (Ref 7).  ***Add a section about H-bonding of the ligand with the Lb and how the heme group fits into the molecule***