title: Structure of chain d of the gigantic hemoglobin of the earthworm.
abstract: The extracellular hemoglobin of the earthworm has four major O2-binding chains, a, b, c and d, together with additional non-heme structural chains that are required for assembly. Although the abc trimer self-associates extensively at least to (abc)10, addition of chain d results in the formation of a discrete 280 kDa complex corresponding to (abcd)4. Thus a primary function of chain d is to cap the abc association and convert an abc trimer that binds O2 with weak cooperativity to a highly cooperative (abcd)4 complex. Amino-acid sequences of the major globin chains a, b, c have been determined previously by peptide and cDNA analysis. However, the peptide sequence reported for the major chain d (Shishikura, F., Snow, J.W., Gotoh, T., Vinogradov, S.N. and Walz, D.A. (1987) J. Biol. Chem., 262. 3123-3131), has a calculated molecular mass 134-167 Da higher than masses for components of chain d determined by mass spectrometry (Owrby, D.W., Zhu, H., Schneider, K., Beavis, R.C., Chait, B.T. and Riggs, A.F. (1993) J. Biol. Chem. 268, 13539-13547). Reverse-phase HPLC confirms the presence of two distinct polypeptides, d1 and d2, together with d'1, a variant of d1, cDNA derived amino acid sequences have been determined for chains d'1 and d2 by application of the polymerase chain reaction with primers based on the NH2-terminal sequences and oligo-dT. Each of the two cDNA-derived sequences has 140 residues and they differ by 28 substitutions. The data show that the sequence originally reported had been derived from peptides generated from both polypeptides.
authors.affiliation: Department of Zoology, University of Texas, Austin 78712, USA.
authors.forename: Q
authors.initials: Q
authors.lastname: Xie
authors.forename: R A
authors.initials: RA
authors.lastname: Donahue
authors.forename: K
authors.initials: K
authors.lastname: Schneider
authors.forename: U A
authors.initials: UA
authors.lastname: Mirza
authors.forename: I
authors.initials: I
authors.lastname: Haller
authors.forename: B T
authors.initials: BT
authors.lastname: Chait
authors.forename: A F
authors.initials: AF
authors.lastname: Riggs
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002851:Chromatography, High Pressure Liquid; D018076:DNA, Complementary / Q000235:genetics; D005914:Globins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification; D006454:Hemoglobins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D015394:Molecular Structure; D008970:Molecular Weight; D009835:Oligochaeta / Q000737:chemistry* / Q000235:genetics; D011487:Protein Conformation
chemical_list: D018076:DNA, Complementary; D006454:Hemoglobins; D005914:Globins