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Sequence-divergent units of the ABA-1 polyprotein array of the nematode Ascaris suum have similar fatty-acid- and retinol-binding properties but different binding-site environments

  • Lindsay McDermott
    ,
  • Joyce Moore
    ,
  • Nicholas C. Price
    ,
  • Sharon M. Kelly
    ,
  • Alan Cooper
    ,
  • Malcolm W. Kennedy
  • University of Glasgow
    ,
  • University of Stirling
Research Output: Contribution to journal Article Peer-review

Abstract

Polyproteins comprise long polypeptides that are post-translationally cleaved into proteins of different function, or tandemly repetitive polypeptides which are processed into multiple versions of proteins which are presumed to have the same function. In the latter case the individual units of the polyprotein can differ substantially in sequence. Identity of function between the different units therefore cannot be assumed. Here we have examined the ABA-1 polyprotein allergen of the parasitic nematode Ascaris suum and found it to contain units which show a 50% difference in amino acid sequence. The parasite therefore produces at least two radically different forms of the allergen encoded within the polyprotein array. In fluorescence-based ligand-binding assays, recombinant polypeptides representing the two forms (designated ABA-1A1 and ABA-1B1) showed similar binding affinities for a range of fluorescent active-site probes [retinol, dansylundecanoic acid, dansyl-DL-alpha-amino-octanoic acid, cis-parinaric acid (cPnA)] and for the non-specific hydrophobic surface probe 8-anilinonaphthalene-1-sulphonic acid. However, the molecular environments in the active sites are markedly different, as indicated by disparate fluorescence emission peaks and intensities of bound probes. CD showed that the proteins have similar secondary structures but differ in susceptibility to chemical denaturation/unfolding by guanidinium chloride. Both retain a single conserved tryptophan residue in a characteristic non-polar environment, as revealed by extreme fluorescence blue shift. Thus the gross differences in sequence of the two proteins are not reflected in their ligand-binding specificities but in their binding-site environments.

Publication Information

Output type

Research Output: Contribution to journal Article Peer-review

Original language

English

Pages from-to (Number of pages)

Pages 337-343

Journal (Volume, Issue Number)

Biochemical Journal (Volume 340)

Publication milestones

  • Published - 15/05/1999

Publication status

Published - 15/05/1999

ISSN

0264-6021

External Publication IDs

  • handle.net: 10547/622680
  • Scopus: 0033563080

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