Structural characterization of CalO2: a putative orsellinic acid P450 oxidase in the calicheamicin biosynthetic pathway

Proteins. 2009 Jan;74(1):50-60. doi: 10.1002/prot.22131.


Although bacterial iterative Type I polyketide synthases are now known to participate in the biosynthesis of a small set of diverse natural products, the subsequent downstream modification of the resulting polyketide products remains poorly understood. Toward this goal, we report the X-ray structure determination at 2.5 A resolution and preliminary characterization of the putative orsellenic acid P450 oxidase (CalO2) involved in calicheamicin biosynthesis. These studies represent the first crystal structure for a P450 involved in modifying a bacterial iterative Type I polyketide product and suggest the CalO2-catalyzed step may occur after CalO3-catalyzed iodination and may also require a coenzyme A- (CoA) or acyl carrier protein- (ACP) bound substrate. Docking studies also reveal a putative docking site within CalO2 for the CLM orsellinic acid synthase (CalO5) ACP domain which involves a well-ordered helix along the CalO2 active site cavity that is unique compared with other P450 structures.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Acyl Carrier Protein / metabolism
  • Animals
  • Bacterial Proteins / chemistry*
  • Bacterial Proteins / metabolism*
  • Biosynthetic Pathways
  • Coenzyme A / metabolism
  • Crystallography, X-Ray
  • Escherichia coli / genetics
  • Iodine / metabolism
  • Ligands
  • Micromonospora / enzymology*
  • Micromonospora / genetics
  • Micromonospora / metabolism
  • Oxidoreductases / chemistry
  • Oxidoreductases / metabolism
  • Polyketide Synthases / chemistry*
  • Polyketide Synthases / metabolism*
  • Protein Binding
  • Protein Structure, Tertiary
  • Resorcinols / metabolism
  • Streptomyces / genetics


  • Acyl Carrier Protein
  • Bacterial Proteins
  • Ligands
  • Resorcinols
  • orsellinic acid
  • Polyketide Synthases
  • Iodine
  • Oxidoreductases
  • Coenzyme A