Metalloglobins

Metalloglobins are a superfamily of proteins characterized by their ability to bind a heme prosthetic group, which contains an iron atom. This iron atom is crucial for their diverse physiological functions, which often involve oxygen transport, storage, or electron transfer. The globin fold, a common structural motif, provides a specific pocket for the heme group, allowing for precise positioning of the iron atom and interaction with various ligands.

Hemoglobin, the most well-known metalloglobin, is responsible for oxygen transport in the blood of vertebrates. Myoglobin, found in muscle tissue, serves as an oxygen store. Other members of the metalloglobin family include neuroglobins, which are found in the brain and may play roles in oxygen sensing or neuroprotection, and cytoglobin, located in various tissues and implicated in cellular respiration and signaling.

The iron atom within the heme group can exist in different oxidation states, allowing metalloglobins to participate in redox reactions. This redox activity is exploited in enzymes like cytochromes, although these are often categorized separately. The reversible binding of oxygen to the ferrous (Fe2+) state of the heme iron is a hallmark of many metalloglobins, enabling efficient oxygen uptake and release. Substitutions in the amino acid residues surrounding the heme pocket can significantly influence the oxygen binding affinity and other functional properties of these proteins.