Probing a novel potato lipoxygenase with dual positional specificity reveals primary determinants of substrate binding and requirements for a surface hydrophobic loop and has implications for the role of lipoxygenases in tubers

Biochem J. 2001 Jan 15;353(Pt 2):345-55. doi: 10.1042/0264-6021:3530345.

Abstract

A new potato tuber lipoxygenase full-length cDNA sequence (lox1:St:2) has been isolated from potato tubers and used to express in Escherichia coli and characterize a novel recombinant lipoxygenase (potato 13/9-lipoxygenase). Like most plant lipoxygenases it produced carbonyl compounds from linoleate (the preferred substrate) and was purified in the Fe(II) (ferrous) state. Typical of other potato tuber lipoxygenases, it produced 5-HPETE [5(S)-hydroperoxy-(6E, 8Z, 11Z, 14Z)-eicosatetraenoic acid] from arachidonate. In contrast to any other potato tuber lipoxygenase, it exhibited dual positional specificity and produced roughly equimolar amounts of 13- and 9-hydroperoxides (or only a slight molar excess of 9-hydroperoxides) from linoleate. We have used a homology model of pea 9/13-lipoxygenase to superimpose and compare the linoleate-binding pockets of different potato lipoxygenases of known positional specificity. We then tested this model by using site-directed mutagenesis to identify some primary determinants of linoleate binding to potato 13/9-lipoxygenase and concluded that the mechanism determining positional specificity described for a cucumber lipoxygenase does not apply to potato 13/9-lipoxygenase. This supports our previous studies on pea seed lipoxygenases for the role of pocket volume rather than inverse orientation as a determinant of dual positional specificity in plant lipoxygenases. We have also used deletion mutagenesis to identify a critical role in catalysis for a surface hydrophobic loop in potato 13/9-lipoxygenase and speculate that this may control substrate access. Although potato 13/9-lipoxygenase represents only a minor isoform in tubers, such evidence for a single lipoxygenase species with dual positional specificity in tubers has implications for the proposed role of potato lipoxygenases in the plant.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Binding Sites
  • Cloning, Molecular
  • Escherichia coli / metabolism
  • Hydrogen-Ion Concentration
  • Lipoxygenase / chemistry
  • Lipoxygenase / genetics
  • Lipoxygenase / metabolism*
  • Models, Molecular
  • Molecular Sequence Data
  • Mutagenesis, Site-Directed
  • Phylogeny
  • Plant Proteins / metabolism*
  • Solanum tuberosum / enzymology*
  • Substrate Specificity

Substances

  • Plant Proteins
  • Lipoxygenase

Associated data

  • GENBANK/Y18548