De novo design and spectroscopic characterization of Cu(II)-binding peptides based upon the blue copper protein plastocyanin

Due to the character of the original source materials and the nature of batch digitization, quality control issues may be present in this document. Please report any quality issues you encounter to digital@library.tamu.edu, referencing the URI of the item.Includes bibliographical references (leaves 83-90).Issued also on microfiche from Lange Micrographics.Blue copper proteins have long held the interest of inorganic chemists, partially because of the interesting spectroscopic properties of the proteins and partially because of the difficulty in synthesizing an inorganic model complex that mimics those spectroscopic properties. Most blue copper proteins are similar to either plastocyanin or azurin, the best characterized of the blue copper proteins. All blue copper proteins contain a coordination site where Cu(II) is bound in a trigonal plane of two histidine ligands and one cysteine. Most of the proteins have weak axial interactions. The Cu(II) in plastocyanin has one axial interaction with a thioether from a methionine giving it a flattened tetrahedral overall geometry, and in azurin there are two axial interactions, one from the methionine and another from a backbone carbonyl of a glycine. The role of the axial ligands seems to be to tune the reduction potential of the Cu(II) site in these electron transfer proteins. It was not until recent years that inorganic complexes have come close to mimicking the spectroscopic properties of the protein sites. The study presented in this work focuses on determining the requirements for creation and stabilization of the blue copper site. Two peptides, BCP-A and BCP-B are designed to bind Cu(II) utilizing either the ligand loop from Poplar plastocyanin, BCP-A, or the blue copper ligand set placed about a central β-turn, BCP-B. The designed peptides both bind Cu(II) and the spectroscopic characterization of the BCP-Cu(II) complexes is presented. BCP-A-Cu(II) forms a tetragonal complex with some degree of tetrahedral twist in the square plane, while BCP-B-Cu(II) has little or no twist associated with the square plane in the tetragonal complex. The spectroscopic studies reveal that both peptides are coordinating to the Cu(II) with the cysteine thiolate and two hitidine nitrogen ligands. Evidence for the axial interactions with the BCP-Cu(II) complexes is observed with ENDOR spectroscopy. The BCP-Cu(II) reduction potentials have been measured to be + 62 mV vs. NHE for BCP-A-Cu(II) and -11 mV vs. NHE for BCP-B-Cu(II). The observed redox potentials fit a trend observed for the blue copper proteins, as the axial interactions are increased the reduction potential decreases. From a comparison of the BCP-A-Cu(II) and BCP-B-Cu(II) properties it is evident that the ligand loop from plastocyanin is involved in creating and stabilizing the blue copper site, however, by itself it is not enough to create the blue copper site