Expression, characterization, and crystallization of oxygen-avid Ascaris hemoglobin domains

A. P. Kloek, J. Yang, F. S. Mathews, D. E. Goldberg

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The Ascaris perienteric hemoglobin is 104 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.

Original languageEnglish
Pages (from-to)17669-17671
Number of pages3
JournalJournal of Biological Chemistry
Issue number24
StatePublished - 1993


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