ABSTRACT
HGbIV is unique truncated hemoglobin (tHb) that differs from other bacterial tHbs due to its large size, polar heme pocket residues and large cavity for exogenous ligand in the heme pocket. The crystal structures of HGbIV showed that its heme pocket can accommodate and interact with bulky PO4-3 ion. Here, we have docked different smaller molecules/ion like O2, NO, CO, CO2, NO3-1, CH3COO-1 and CN-1 in the heme pocket of HGbIV. Analysis of the structure showed that the smaller ligands docked far away from most of the heme pocket residues namely His70(B9), His71(B10), Ser97(E11) and Trp137(G8), and only PO4-3 docked at a position where it can interact with all these residues. It appears that HGbIV is not designed for transport of smaller gaseous molecule like the other heme containing proteins and it may be a phosphate sensor.
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