J Biol Chem, Vol. 273, Issue 22, 13583-13592, May 29, 1998

Characterization of the Myoglobin and Its Coding Gene of the Mollusc Biomphalaria glabrata

Sylvia Dewilde, Birgitta Winnepenninckx^§, Marcio H. L. Arndt^¶, Danielle G. Nascimento^¶, Marcelo M. Santoro^¶, Matty Knight, Andre N. Miller, Anthony R. Kerlavage^**, Neil Geoghagen^**, Eric Van Marck, Leo X. Liu^§§, Roy E. Weber^¶¶, and Luc Moens

From the Departments of  Biochemistry and  Medicine, University of Antwerp, B-2610 Antwerp, Belgium, ^§ Koninklijk Belgisch Instituut voor Natuurwetenschappen, B-1000 Brussels, Belgium, ^¶ Departamento de Bioquimica e Imunologia, Instituto de Ciencias Biologicas, Universidade Federal de Minas Gerais, Belo Horizonte, Brasil,  Biomedical Research Institute, Rockville, Maryland 20852, the ^** Institute for Genome Research, Rockville, Maryland 20850, the ^§§ Harvard-Thorndike Laboratory, Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston Massachusetts 02215, and the ^¶¶ Department of Zoophysiology, University of Aarhus, DK-8000 Aarhus C, Denmark

A cDNA clone isolated from a Biomphalaria glabrata (Mollusca, Gastropoda) neural cDNA library was identified as encoding a myoglobin-like protein of 148 amino acids with a single domain and a calculated mass of 16,049.29. Alignment with globin sequences with known tertiary structure confirms its overall globin nature.

The expressed myoglobin was identified in the radular muscle and isolated. Oxygen equilibrium measurements on the protein reveal a high oxygen affinity. Val-B10 and Gln-E7, important residues for the determination of the oxygen affinity, are strikingly different from the standard molluscan pattern (Conti, E., Moser, C., Rizzi, M., Mattevi, A., Lionetti, C., Coda, A., Ascenzi, P., Brunori, M., Bolognesi, M. (1993) J. Mol. Biol. 233, 498-508).

The single gene encoding the globin chain is interrupted by three introns at positions A3.2, B12.2, and G7.0. Comparison with other nonvertebrate globin genes reveals on the one hand conservation (B12.2 and G7.0) and on the other hand variability of the insertion positions (A3.2). The Biomphalaria myoglobin sequence was used together with all other molluscan globin sequences available to assess the origin and phylogeny of the phylum. Our results confirm the doubts raised about monophyletic origin of the Mollusca, which was first observed using SSU rRNA as a molecular marker.