Single tryptophanyl substitutions affect the structure of apomyoglobin
Sirangelo, I.; Tavassi, S.; Irace, G.
Bollettino della Societa Italiana di Biologia Sperimentale 74(9-10): 83-89
1998
ISSN/ISBN: 0037-8771 PMID: 10904557 Document Number: 485524
Mammalian myoglobins contain two tryptophanyl residues at the invariant positions A-5 (W7) and A-12 (W14) in the N-terminal region (A helix) of the protein molecule. To determine the contribution of each tryptophanyl residue to the structure and stability of myoglobin, recombinant proteins with single indole residue, i.e., W7 or W14, were obtained by site-directed mutagenesis. The mutant proteins, expressed in Escherichia coli, were found correctly folded, the far ultraviolet circular dichroism of both mutants as well as the Soret absorption being superimposed to that of wild type protein. The removal of the prosthetic group from mutant proteins determined a loss of helical content much larger than that observed in the case of wild type myoglobin. These results suggest that tryptophanyl residues can play a crucial role on globin folding and structure.