A Calixarene with Four Peptide Loops: An Antibody Mimic for Recognition of Protein Surfaces

Abstract

reported that the adenine group in 5'-AMP forms a stronger stacking interaction to bipyridinecopper(1r) complexes than the uracil group in 5'-UMP. ['91 Such a stacking interaction between adenine and bipyridine may account for the high selectivity of 2 for 5a over 5b-d (Table I).Dinuclear complexes 1 and 2 are highly active in promoting hydrolytic cleavage of nucleoside 2',3'-cyclic monophosphates. Furthermore, 1 is highly regioselective and cleaves 5 c and 5 d predominantly to nucleoside 2'-monophosphates.On the other hand, 2 shows remarkable base selectivity and hydrolyzes 5a much faster than 5 b-d. Presumably, 1 achieves high regioselectivity by regioselectively binding to the bases in the substrates, while 2 attains base selectivity by a preferentialx--x stacking interaction between the bipyridine unit in 2 and the bases in the substrates. More experiments are in progress to probe the exact nature of interactions that give rise to the high reactivities and base and regioselectivities shown by 1 and 2. Experimental SectionThe preparation of 1 -4 has been described previously [12]. Cleavage of 5 by 1-4 was followed by HPLC (Ranin). The following procedure is typical: 1 (1.1 mM, 4.5 mL) in a buffer was mixed with 5a (2.0 mM, 0.5 mL) in the same buffer. Aliquots (ZOO pL) of the reaction mixture were quenched with ethylenediaminetetraacetate (EDTA, 20 mM, 200 pL). After any solid that formed was filtered, the quenched solution (20 pL) was injected onto a C-18 reversed-phase column and eluted for 10 min with 1-1070 CH,CN in H 2 0 containing 0.1 % CF,COOH (flow rate l.OmLmin-'). The eluent was monitored at Amax of the nucleobase (260 nm for adenine and uracil, 252 nm for guanine, and 268 nm for cytosine) by a Rainin UV-C detector. The first-order rate constants k were obtained as slopes of plots of In(AdA,) versus t, where AD and A , are integrations of the areas of the HPLC peaks for 5 at f = 0 and I, respectively. Selectivities for the formation of 3monophosphate (6) with respect to 2-monophosphate (7) were calculated from the ratios of integrations of the areas of the HPLC peaks for 6 and 7 The identities of 6 and 7 were established with authetic samples (Sigma). The two isomers have nearly identical extinction coefficients at A,,, of the nucleobase. Therefore, the ratio of the HPLC peaks for 6 and 7 is equal to the ratio of the amounts of 6 and 7 produced (i. e., the regioselectivity). In all cases the ratios remained constant throughout the entire course of hydrolysis. For slow reactions (k < 5 x lo-%'), appreciable amounts of 6 and 7 were further hydrolyzed to give inorganic phosphate and the correponding nucleosides before 5 was completely hydrolyzed. However, the ratio of 6 to 7 in the reaction mixture remained unchanged. Duplicate runs showed measurement errors of less than & 15 % for k and less than *3% for the regioselectivity.

Metal complexes as “protein surface mimetics”

“…3a). 28 A series of derivatives were identified that bind to cytochrome (Cyt) c -chymotrypsin and platelet-derived growth factor (PDGF), acting as antibody mimics. 14,28 30 Most impressively, GFB-111, a PDGF binder with IC50 ~ 250 nM was shown to inhibit tumour growth and angiogenesis in vivo.…”

Modulation of protein–protein interactions by synthetic receptors: Design of molecules that disrupt serine protease–proteinaceous inhibitor interaction

“…Our approach borrows from the essential features of antibody-combining domains and is based on the attachment of several synthetic peptide loops onto a core calixarene scaffold. Interaction with a complementary protein surface can then involve significant contact (Ͼ400 Å 2 ) between the peptide loops and matching regions on the exterior of the protein (8). If binding occurs close to the active site or an area of contact with other proteins, then a disruption of the function of the protein can be anticipated.…”

Selective disruption of protein aggregation by cyclodextrin dimers

“…Other approaches to blocking protein-protein interactions have been reported recently (1,2,(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29), many with peptides or peptide mimics. Our work suggests that the specific binding of hydrophobic side chains by CD dimers that we had reported earlier can be extended to proteins and that it is another way to block protein aggregation.…”