Quantum chemical calculations and mutational analysis suggest heat shock protein 90 catalyzes trans-cis isomerization of geldanamycin.
The affinity of geldanamycin (GA) for binding to heat shock protein 90 (HSP90) is 50- to 100-fold weaker than is the affinity of the structurally distinct natural product radicicol. X-ray crystallography shows that although radicicol maintains its free conformation when bound to HSP90, the conformation of GA is dramatically altered from an extended conformation with a trans amide bond to a kinked shape in which the amide group in the ansa ring has the cis configuration. We have performed ab initio quantum chemical calculations to demonstrate that the trans-cis isomeriztion of GA in solution is both kinetically and thermodynamically unfavorable. Thus, we propose that HSP90 catalyzes the isomerization of GA. We identify Ser113, a conserved residue outside the ATP binding pocket, as essential for the isomerization of GA. In support of this model, we show that radicicol binds equally well to both wild-type HSP90 and the Ser113 mutant, whereas the binding of GA to the Ser113 mutant is decreased significantly from its binding to wild-type HSP90. Based on this finding, a mechanism of keto-enol tautomerization of GA catalyzed by HSP90 is proposed. The added requirement of isomerization prior to tight binding may explain the enhanced binding affinity of GA for HSP90 in a cell extract versus in a purified form.
Center for Molecular Modeling, Center for Information Technology, National Institutes of Health, Building 12A, Room 2049, Bethesda, Maryland 20892, USA. leeys@mail.nih.gov
Yong-Sok
YS
Lee
Monica G
MG
Marcu
Len
L
Neckers
D000255:Adenosine Triphosphate / Q000378:metabolism; D016227:Benzoquinones; D002384:Catalysis; D018360:Crystallography, X-Ray; D018841:HSP90 Heat-Shock Proteins / Q000737:chemistry / Q000378:metabolism; D007536:Isomerism; D047029:Lactams, Macrocyclic; D011789:Quantum Theory; D011809:Quinones / Q000737:chemistry*; D012694:Serine / Q000378:metabolism; D013816:Thermodynamics
D016227:Benzoquinones; D018841:HSP90 Heat-Shock Proteins; D047029:Lactams, Macrocyclic; D011809:Quinones; D012694:Serine; D000255:Adenosine Triphosphate; C001277:geldanamycin