Cloning, overexpression and characterization of micro-myoglobin, a minimalheme-binding fragment

We report the cloning and expression of micro-myoglobin, a 78-amino-acid fr agment containing residues 29-105 of sperm whale myoglobin, and spanning th e region from mid-helix B to mid-helix G of the globin fold. In contrast to full-length myoglobin and to mini-myoglobin (residues 32-129), the micro-m yoglobin apoprotein is almost unfolded. However, circular dichroism and abs orption spectroscopy data indicate that this fragment is capable of folding into a functional heme-binding unit forming a complex with the prosthetic group with characteristics similar to native myoglobin. Therefore, this cas e represents a new example of cofactor-assisted folding. The experimental d ata suggest independence between myoglobin subdomains.