| Abstract
| - Catalytic esterase peptide dendrimers with a core active site were discovered by functionalscreening of a 65 536-member combinatorial library of third-generation peptide dendrimers using fluorogenic1-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 thedendrimer core. A pair of arginine residues in the first-generation branch assists substrate binding. Thecatalytic proficiency of dendrimer RMG3 (kcat/KM = 860 M-1 min-1 at pH 6.9) per catalytic site is comparableto 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 branchesconsisting of aromatic amino acids. These interactions take place in a relatively compact conformationsimilar 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 histidineresidues is unaffected by the outer dendritic layers. Dendrimer HG3 or its core HG1 exhibit comparableactivity to the first-generation dendrimer A1 ((AcHisSer)2DapHisSerNH2). The compactness of dendrimerHG3 in solution is close to that a denatured peptide. These experiments document the first esterase peptidedendrimer enzyme models with a single catalytic site and suggest a possible relationship between packingand catalysis in these systems.
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