Oxygen transport proteins: III. Structural studies of the scorpion (Buthus sindicus) hemocyanin, partial primary structure of its subunit Bsin1

Syed Abid Ali, Atiya Abbasi, Stanka Stoeva, Rakez Kayed, Pavlina Dolashka-Angelova, Heinz Schwarz, Wolfgang Voelter

Research output: Contribution to journalArticle

4 Scopus citations

Abstract

The hemocyanin (Hc) from Buthus sindicus, studied in the native state, demonstrated to be an aggregate of eight different types of subunits arranged in four cubic hexamers. Both, the 'top' and the 'side' views of the native molecule have been identified from the negatively stained specimens using transmission electron microscopy. Out of these, eight different polypeptide chains, the partial primary structure (68%) of a subunit Bsin1 (M(r) = 72422.7 Da) was established using a combination of automated Edman degradation and mass spectrometry. A multiple sequence alignment with other closely related cheliceratan Hc subunits revealed average identities of ca. 60%. Most of the structurally important residues, i.e. copper and calcium- binding ligands, as well as the residues involved in the presumed oxygen entrance pathway, proved to be strictly conserved in Bsin1. Sequence variations have been observed around the functionally important chloride- binding site, not only for the B. sindicus subunit Bsin1, but also for the subunit Aaus-6 of the scorpion A. australis and the subunit Ecal-a from the spider Eurypelma californicum Hcs. Deviation in the primary structure related to the chloride-binding site suggest that the effect of chloride ions may vary in different hemocyanins. Furthermore, the secondary structural contents of the Hc subunit Bsin1 were determined by circular dichroism revealing ca. 33% α-helix, 18% β-sheet, 19% β-turn, and 30% random coil composition. These values are in good agreement with the crystal structure of the closely related Hc subunit Lpol-II from horseshoe crab L. polyphemus. Electron microscopic studies of the purified Hc subunit under native conditions revealed that Bsin1 has self aggregation properties. Results of these studies are discussed. (C) 2000 Elsevier Science Inc.

Original languageEnglish (US)
Pages (from-to)361-376
Number of pages16
JournalComparative Biochemistry and Physiology - B Biochemistry and Molecular Biology
Volume126
Issue number3
DOIs
StatePublished - Jan 1 2000
Externally publishedYes

Keywords

  • Arthropod
  • Buthus sindicus
  • Chelicerata
  • Hemocyanin
  • Oxygen carrier proteins
  • Primary structure
  • Scorpion
  • Secondary structure

ASJC Scopus subject areas

  • Biochemistry
  • Physiology
  • Molecular Biology

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