title: Functional and structural characterization of the myoglobin from the polychaete Ophelia bicornis.
abstract: The myoglobin of the polychaete annelid Ophelia bicornis was isolated, purified to homogeneity and characterized. The primary structure, obtained from cDNA and protein sequencing, consists of 139 amino acid residues. The alignment with other globin sequences showed that O. bicornis myoglobin misses the pre-A helix and the first six residues of the A helix. The presence of a PheB10-GlnE7 haem distal residue pair is in agreement with the measured oxygen affinity (P50=0.85 mmHg; 1 mmHg=0.133 kPa) and the only slightly higher autoxidation rate constant (0.28 h(-1)) with respect to that of the sperm whale myoglobin mutant E7 His-->Gln (0.21 h(-1)) and to elephant myoglobin (0.1 h(-1)). Oxygen-binding co-operativity was found to be absent under all the examined experimental conditions. The resistance of O. bicornis myoglobin towards autoxidation seems to confirm the important role of part of the A helix in the stability of the globin. The higher pKa of the acid-alkaline ferric transition of O. bicornis with respect to Asian elephant myoglobin, as well as the higher absorbance ratio of its ferric form to the oxy form measured in the Soret region (gammamet/gammaoxy) with respect to that of the African elephant myoglobin, suggested a stronger interaction between the distal glutamine and the water molecule at the sixth co-ordinate position.
authors.affiliation: Dipartimento di Scienze Applicate ai Biosistemi, Università di Cagliari, Cittadella Universitaria, I-09042 Monserrato, CA, Italy. sanna@unica.it
authors.forename: M Teresa
authors.initials: MT
authors.lastname: Sanna
authors.forename: Barbara
authors.initials: B
authors.lastname: Manconi
authors.forename: Massimo
authors.initials: M
authors.lastname: Castagnola
authors.forename: Bruno
authors.initials: B
authors.lastname: Giardina
authors.forename: Daniela
authors.initials: D
authors.lastname: Masia
authors.forename: Irene
authors.initials: I
authors.lastname: Messana
authors.forename: Alessandra
authors.initials: A
authors.lastname: Olianas
authors.forename: Maria
authors.initials: M
authors.lastname: Patamia
authors.forename: Raffaele
authors.initials: R
authors.lastname: Petruzzelli
authors.forename: Mariagiuseppina
authors.initials: M
authors.lastname: Pellegrini
mesh_terms: D000494:Allosteric Regulation; D000495:Allosteric Site; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D018076:DNA, Complementary / Q000235:genetics; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008969:Molecular Sequence Data; D009211:Myoglobin / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism; D011077:Polychaeta / Q000737:chemistry*; D011485:Protein Binding; D017386:Sequence Homology, Amino Acid; D021241:Spectrometry, Mass, Electrospray Ionization; D017186:Titrimetry
chemical_list: D018076:DNA, Complementary; D009211:Myoglobin; D010100:Oxygen