An azacrown-functionalized peptide as a metal ion based catalyst for the cleavage of a RNA-model substrate

The previously synthesized terminally blocked heptapeptide Ac-Aib-ATANP-Aib -Aib- ATANP-Aib-Aib-OMe (1a). where ATANP is (S)-2-amino-3-(1,4,7-triazacyc lononane)]propanoic acid and Aib is alpha -aminoisobutyric acid, which is s oluble in neutral water where it largely adopts a 3(10)-helical conformatio n, has been studied, as bimetallic complex [metal ions: Cu(H). Ni(II), Zn(I I)], for the transphosphorylation catalysis of the RNA-model substrate 2-(h ydroxypropyl)-p-nitrophenyl phosphate (HPNP). A detailed analysis was carri ed out with the Zn(II) dinuclear complex. Comparison with the mononuclear Z n(II) complex with 1,4,7-triazacyclononane (3) points to cooperativity betw een the two Zn(II) ions in the process catalyzed by 1a-2Zn(II). On the cont rary the dinuclear Zn(II) complex of dipeptide Ac-(ATANP)(2)-OMe (2), lacki ng any ordered conformation. is less active than 3-Zn(II). The kinetic anal ysis suggests the following: (a) the peptide is conformationally very robus t and does not loose activity up to 50 degreesC; (b) the substrate binds to the peptide-Zn(II) complex, although not all modes of complexation allow u s to take advantage of the cooperativity between the two metal centers. The maximum rare acceleration estimated at pH 7 for the fully bound substrate is ca. 200-fold compared with the uncatalyzed process. (C) 2001 John Wiley & Sons, Inc.