title: Expression, characterization, and crystallization of oxygen-avid Ascaris hemoglobin domains.
abstract: The Ascaris perienteric hemoglobin is 10(4) times more oxygen-avid than mammalian hemoglobins. Inspection of its primary structure fails to explain this extraordinary association with oxygen. The Ascaris hemoglobin gene encodes a 40-kDa, two-domain globin; the two domains (D1 and D2) are 63% identical, and each is capable of binding a single heme. The native protein is an octamer. At the end of D2 is a highly charged carboxyl-terminal extension containing four direct repeats of HKEE. We have expressed the two domains separately in E. coli. Both individual domains are extremely oxygen-avid. D2, with attached COOH-terminal tail, is capable of multimerization, whereas D1 remains a monomer. Recombinant D1 readily forms diffractable, red, prismatic crystals. We conclude that: 1) the basis of the hemoglobin's oxygen avidity rests in an isolated heme pocket and does not involve inter-domain interactions and 2) multimerization is mediated through sequences in the second domain, most probably via the charged COOH-terminal tail.
authors.affiliation: Department of Medicine, Washington University School of Medicine, St. Louis, Missouri 63110.
authors.forename: A P
authors.initials: AP
authors.lastname: Kloek
authors.forename: J
authors.initials: J
authors.lastname: Yang
authors.forename: F S
authors.initials: FS
authors.lastname: Mathews
authors.forename: D E
authors.initials: DE
authors.lastname: Goldberg
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017165:Ascaris suum / Q000378:metabolism*; D003001:Cloning, Molecular; D003460:Crystallization; D004247:DNA; D006454:Hemoglobins / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D008969:Molecular Sequence Data; D010100:Oxygen / Q000378:metabolism; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism
chemical_list: D006454:Hemoglobins; D011994:Recombinant Proteins; D004247:DNA; D010100:Oxygen