Synthetic models for the zinc sites in the methionine synthases.
The syntheses and molecular structures of a series of tetrahedral zinc complexes designed to model the active sites in Escherichia coli methionine synthases are reported. [PhTttBu]ZnBr (PhTttBu = phenyltris((tert-butylthio)-methyl)borate) was prepared and characterized crystallographically to provide entry into [S3]ZnX complexes. Metathesis with KSPh yielded the phenylthiolato complex, [PhTttBu]Zn(SPh), which represents a structural mimic of the homocysteine ligated form of the enzyme. Alternatively, [S2N]ZnX (X = Br, CH3, SPh) species were prepared using the new mixed-donor ligands, [Ph(pz)BttBu] (phenyl(pyrazolyl)bis((tert-butylthio)methyl)borate) and [Ph(pztBu)BttBu] (phenyl(3-tert-butylpyrazolyl)bis((tert- butylthio)methyl)borate). Protonolysis of [Ph(pztBu)-BttBu]Zn(CH3) by PhSH in toluene yielded [Ph(pztBu)BttBu]Zn(SPh), a synthetic analogue of the homocysteine ligated form of cobalamin-independent methionine synthase (Met E). The average Zn-S bond distance in [Ph-(pztBu)BttBu]Zn(SPh) of 2.37 A compares well with the EXAFS-derived distance of 2.31 A found in the homocysteine-bound form of Met E.
Chiou
S J
SJ
Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, USA.
Innocent
J
J
Riordan
C G
CG
Lam
K C
KC
Liable-Sands
L
L
Rheingold
A L
AL
D013766:5-Methyltetrahydrofolate-Homocysteine S-Methyltransferase / Q000737:chemistry*; D008956:Models, Chemical; D015394:Molecular Structure; D015032:Zinc / Q000737:chemistry*
D013766:5-Methyltetrahydrofolate-Homocysteine S-Methyltransferase; D015032:Zinc