Downstream reaction of cisplatin with methionine-containing peptides: pH-dependent competition between hydrolytic cleavage and macrochelation

Mechanism of peptide hydrolysis by co-catalytic metal centers containing leucine aminopeptidase enzyme: a DFT approach

In this density functional theory study, reaction mechanisms of a co-catalytic binuclear metal center (Zn1-Zn2) containing enzyme leucine aminopeptidase for two different metal bridging nucleophiles (H(2)O and -OH) have been investigated. In addition, the effects of the substrate (L-leucine-p-nitroanilide → L-leucyl-p-anisidine) and metal (Zn1 → Mg and Zn2 → Co, i.e., Mg1-Zn2 and Mg1-Co2 variants) substitutions on the energetics of the mechanism have been investigated. The general acid/base mechanism utilizing a bicarbonate ion followed by this enzyme is divided into two steps: (1) the formation of the gem-diolate intermediate, and (2) the cleavage of the peptide bond. With the computed barrier of 17.8 kcal/mol, the mechanism utilizing a hydroxyl nucleophile was found to be in excellent agreement with the experimentally measured barrier of 18.7 kcal/mol. The rate-limiting step for reaction with L-leucine-p-nitroanilide is the cleavage of the peptide bond with a barrier of 17.8 kcal/mol. However, for L-leucyl-p-anisidine all steps of the mechanism were found to occur with similar barriers (18.0-19.0 kcal/mol). For the metallovariants, cleavage of the peptide bond occurs in the rate-limiting step with barriers of 17.8, 18.0, and 24.2 kcal/mol for the Zn1-Zn2, Mg1-Zn2, and Mg1-Co2 enzymes, respectively. The nature of the metal ion was found to affect only the creation of the gem-diolate intermediate, and after that all three enzymes follow essentially the same energetics. The results reported in this study have elucidated specific roles of both metal centers, the nucleophile, indirect ligands, and substrates in the catalytic functioning of this important class of binuclear metallopeptidases.

Reaction of platinum(II) diamine and triamine complexes with selenomethionine

We have reacted [Pt(dien)Cl]Cl, [Pt(en)(D(2)O)(2)](2+), and [Pt(Me(4)en)(D(2)O)(2)](2+) [Me(4)en = N,N,N',N'-tetramethylethylenediamine] with selenomethionine (SeMet). When [Pt(dien)Cl]Cl is reacted with SeMet, [Pt(dien)(SeMet-Se)](2+) is formed; two Se-CH(3) resonances are observed due to the different chiralities at the Se atom upon platination. In a reaction of [Pt(dien)Cl]Cl with an equimolar mixture of SeMet and Met, the SeMet product forms more quickly though a slow equilibrium with approximately equal amounts of both products is reached. [Pt(Me(4)en)(D(2)O)(2)](2+) reacts with SeMet to form [Pt(Me(4)en)(SeMet-Se)(D(2)O)](2+) initially but forms [Pt(Me(4)en)(SeMet-Se,N)](+) ultimately. One stereoisomer of the chelate, assigned to the R chirality at the Se atom, dominates within the first few minutes of reaction. [Pt(en)(D(2)O)(2)](2+) forms a variety of products depending on reaction stoichiometry; when one equivalent or less of SeMet is added, the dominant product is [Pt(en)(SeMet-Se,N)](+). In the presence of excess SeMet, [Pt(en)(SeMet-Se)(2)](2+) is the dominant initially, but displacement of the en ligand occurs leading to [Pt(SeMet-Se,N)(2)] as the eventual product. Displacement of the en ligand from [Pt(en)(SeMet-Se,N)](+) does not occur. In reactions of K(2)PtCl(4) with two equivalents of SeMet, [Pt(SeMet-Se,N)(2)] is formed, and three sets of resonances are observed due to different chiralities at the Se atoms. Only the cis geometric isomers are observed by (1)H and (195)Pt NMR spectroscopy.

Coordination of platinum therapeutic agents to met-rich motifs of human copper transport protein1

Platinum therapeutic agents are widely used in the treatment of several forms of cancer. Various mechanisms for the transport of the drugs have been proposed including passive diffusion across the cellular membrane and active transport via proteins. The copper transport protein Ctr1 is responsible for high affinity copper uptake but has also been implicated in the transport of cisplatin into cells. Human hCtr1 contains two methionine-rich Mets motifs on its extracellular N-terminus that are potential platinum-binding sites: the first one encompasses residues 7-14 with amino acid sequence Met-Gly-Met-Ser-Tyr-Met-Asp-Ser and the second one spans residues 39-46 with sequence Met-Met-Met-Met-Pro-Met-Thr-Phe. In these studies, we use liquid chromatography and mass spectrometry to compare the binding interactions between cisplatin, carboplatin and oxaliplatin with synthetic peptides corresponding to hCtr1 Mets motifs. The interactions of cisplatin and carboplatin with Met-rich motifs that contain three or more methionines result in removal of the carrier ligands of both platinum complexes. In contrast, oxaliplatin retains its cyclohexyldiamine ligand upon platinum coordination to the peptide.