Diverse clinical compounds alter the quaternary structure and inhibit the activity of an essential enzyme

ChemMedChem. 2011 Jun 6;6(6):1067-73. doi: 10.1002/cmdc.201100009. Epub 2011 Apr 19.


An in vitro evaluation of the Johns Hopkins Clinical Compound Library demonstrates that certain drugs can alter the quaternary structure of an essential human protein. Human porphobilinogen synthase (HsPBGS) is an essential enzyme involved in heme biosynthesis; it exists as an equilibrium of high-activity octamers, low-activity hexamers, and alternate dimer configurations that dictate the stoichiometry and architecture of further assembly. Decreased HsPBGS activity is implicated in toxicities associated with lead poisoning and 5-aminolevulinate dehydratase (ALAD) porphyria, the latter of which involves hexamer-favoring HsPBGS variants. A medium-throughput native PAGE mobility-shift screen coupled with evaluation of hits as HsPBGS inhibitors revealed 12 drugs that stabilize the HsPBGS hexamer and inhibit HsPBGS activity in vitro. A detailed characterization of these effects is presented. Drug inhibition of HsPBGS in vivo by inducing hexamer formation would constitute an unprecedented mechanism for side effects. We suggest that small-molecule perturbation of quaternary structure equilibria be considered as a general mechanism for drug action and side effects.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Drug-Related Side Effects and Adverse Reactions*
  • Humans
  • Porphobilinogen Synthase / antagonists & inhibitors*
  • Porphobilinogen Synthase / chemistry
  • Porphobilinogen Synthase / metabolism*
  • Protein Multimerization / drug effects
  • Protein Structure, Quaternary / drug effects*


  • Porphobilinogen Synthase