Using diastereopeptides to control metal ion coordination in proteins
2008
Peacock, Anna F.A. | Hemmingsen, Lars | Pecoraro, Vincent L.
Here, we report a previously undescribed approach for controlling metal ion coordination geometry in biomolecules by reorientating amino acid side chains through substitution of L- to D-amino acids. These diastereopeptides allow us to manipulate the spatial orientation of amino acid side chains to alter the sterics of metal binding pockets. We have used this approach to design the de novo metallopeptide, Cd(TRIL12LDL16C)3-, which is an example of Cd(II) bound to 3 L-Cys as exclusively trigonal CdS₃, as characterized by a combination of ¹¹³Cd NMR and ¹¹¹mCd PAC spectroscopy. We subsequently show that the physical properties of such a site, such as the high pKa₂ for Cd(II) binding of 15.1, is due to the nature of the coordination number and not the ligating group. Further more this approach allowed for the design of a construct, GRANDL12LDL16CL26AL30C, capable of independently binding 2 equivalents of Cd(II) to 2 very similar Cys sites as exclusively 3- and 4-, CdS₃ and CdS₃O, respectively. Demonstrating that we are capable of controlling the Cd(II) coordination number in these 2 sites solely by varying the nature of a noncoordinating second coordination sphere amino acid, with D-leucine and L-alanine resulting in exclusively 3- and 4-coordinate structures, respectively. Cd(II) was found to selectively bind to the 4-coordinate CdS₃O site, demonstrating that a protein can be designed that displays metal-binding selectivity based solely on coordination number control and not on the chemical identity of coordinating ligands.
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