Web Release Date: October 9,
A Peptide Dendrimer Enzyme Model with a Single Catalytic Site at the Core
Contribution from the Department of Chemistry and Biochemistry, University of Berne, Freiestrasse 3, 3012 Berne, Switzerland
Received June 23, 2007
Abstract:
Catalytic esterase peptide dendrimers with a core active site were discovered by functional screening of a 65 536-member combinatorial library of third-generation peptide dendrimers using fluorogenic 1-acyloxypyrene-3,6,8-trisulfonates as substrates. In the best catalyst, RMG3, ((AcTyrThr)8(DapTrpGly)4(DapArgSerGly)2DapHisSerNH2), ester hydrolysis is catalyzed by a single catalytic histidine residue at the dendrimer core. A pair of arginine residues in the first-generation branch assists substrate binding. The catalytic proficiency of dendrimer RMG3 (kcat/KM = 860 M-1 min-1 at pH 6.9) per catalytic site is comparable to that of the multivalent esterase dendrimer A3 ((AcHisSer)8(DapHisSer)4(DapHisSer)2DapHisSerNH2) which has fifteen histidines and five catalytic sites (Delort, E. et al. J. Am. Chem. Soc. 2004, 126, 15642-15643). Remarkably, catalysis in the single site dendrimer RMG3 is enhanced by the outer dendritic branches consisting of aromatic amino acids. These interactions take place in a relatively compact conformation similar to a molten globule protein as demonstrated by diffusion NMR. In another dendrimer, HG3 ((AcIlePro)8(DapIleThr)4(DapHisAla)2DapHisLeuNH2) by contrast, catalysis by a core of three histidine residues is unaffected by the outer dendritic layers. Dendrimer HG3 or its core HG1 exhibit comparable activity to the first-generation dendrimer A1 ((AcHisSer)2DapHisSerNH2). The compactness of dendrimer HG3 in solution is close to that a denatured peptide. These experiments document the first esterase peptide dendrimer enzyme models with a single catalytic site and suggest a possible relationship between packing and catalysis in these systems.
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