Identification of variable amino acids in the SRS1 region of CYP6B1 modulating furanocoumarin metabolism

Liping Pan, Zhimou Wen, Jerome Baudry, May R. Berenbaum, Mary A. Schuler

Research output: Contribution to journalArticlepeer-review


The homology model of Papilio polyxenes CYP6B1 places Ile115, one of two variable amino acids, in the SRS1 of various CYP6B subfamily proteins in close proximity to the heme and Ala113, another variable amino acid, in a more distal position. We have constructed mutant CYP6B1 proteins altered at either of these positions and homology models of each based on multiple alignments with crystallized P450 proteins. The homology models suggest the existence of significant structural diversity in the hydrogen bond network surrounding the heme as a result of single point mutations in SRS1. Mutagenesis of Ile115 or Ala113 to other residues present in the insect CYP6B subfamily indicates that these amino acids control the spin state of the heme and, as a result, the catalytic activity of this monooxygenase. In particular, the I115L mutation significantly increases the spin state of the heme coordinately with 2- to 4-fold increases in its turnover of linear furanocoumarins. Other A113V, A113L, A113Q, and A113E mutations display more variation in their effects but, in each case, strong correlations exist between furanocoumarin turnover and heme spin state. These data demonstrate that variable amino acids in SRS1 of the insect CYP6B subfamily exert dramatic effects on the range of furanocoumarins metabolized, even when they occur in positions potentially distal from the substrate. These effects are possibly mediated through rearrangement of the local hydrogen bond network.

Original languageEnglish (US)
Pages (from-to)31-41
Number of pages11
JournalArchives of Biochemistry and Biophysics
Issue number1
StatePublished - Feb 1 2004


  • Catalytic site mutagenesis
  • Furanocoumarin metabolism
  • Homology modeling
  • P450s (P450 monooxygenases)

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Molecular Biology


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