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Model Study on Alkyl-transfer Zinc ProteinSong, Yong-Yi 05 August 2006 (has links)
The thiolate-alkylating protein (Ada protein) is a zinc protein that repairs the defective DNA by transferring methyl group on to itself. We have used the thiophenylphosphine ligand to provide sulfur-rich environment for model study. In this work, we have accidentally found that this zinc complex can activate CH2Cl2 to generate a methylenated complex (4). Carbon-halide activation is commonly used in organic synthesis. However activation of C-Cl bond is comparatively scarce compared to C-Br or C-I bonds.
Varying the degree of deprotonation on the PS3 ligand, a simple zinc dimer (2) can be obtained instead of (4). The dimer (2) can even react with much milder alkyl-reagent, methylphosphotriester. Therefore (2) serves as a successful Ada protein model in this sense. Other related alkyl-transfer reactions using different ligand or zinc complexes were discussed to give insight of the methyl-transfer action of Ada protein.
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Effects of ewe late gestational supplementation of rumen undegradable protein, vitamin E, zinc, and chlortetracycline on ewe productivity and postweaning management of lambs on feedlot performance and tissue depositionRedden, Roy Reid. January 2009 (has links) (PDF)
Thesis (PhD)--Montana State University--Bozeman, 2009. / Typescript. Chairperson, Graduate Committee: Patrick G. Hatfield. Includes bibliographical references.
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Incorporation of histidine-rich metal-binding sites onto small protein scaffolds: implications for imaging, therapeutics, and catalysisSoebbing, Samantha Lynn 01 January 2008 (has links)
Many histidine-rich sites in proteins bind transition metal ions such as Zn2+, natively. Such sites can encourage proper protein folding or allow access to enzymatic capabilities such as hydrolysis. Ru(II) and Tc(I) also bind to aromatic amines providing access to unique chemistries not observed in biology. Ru(II) complexes have shown efficacy in fighting cancer and catalysis, while 99mTc complexes are used in radio-imaging. To incorporate such metal-ions' activities into proteins, several mutants have been designed to bind Zn2+, Ru2+, and Tc1+ by introducing three histidines onto their surfaces. The first design, Z0, utilized a chimeric approach by substituting a turn in engrailed homeodomain for the superimposable Zn2+-binding loop of astacin. In the second design, 3HT-C, three histidine residues were incorporated into the N-terminus of the Trp-cage. The final scaffold, ubiquitin, was used to make two mutants: 3HIU with a 3-histidine containing loop inserted between residues 9 and 10, and 3HPU with 3-histidine point mutations near residues 35-38. Z0 proved unstable due to incorporation of a hydrophobic patch onto its surface and was not able to be isolated in sufficient quantities for study. However, the other proteins were stable and soluble. Zn2+-binding by 3HT-C was investigated by intrinsic tryptophan fluorescence quenching, circular dichroism, and RP-HPLC. Binding by 3HIU and 3HPU was studied by CD. All designed proteins bind to Zn2+ with Kd values in the micromolar range. 3HIU and 3HPU were further studied for their ability to bind Ru(tacn)2+ complexes. While addition of Ru-complexes caused oligomerization to various extents depending upon reaction conditions, homogeneous Ru-protein monomers were purified by a combination of size-exclusion, cation-exchange and immobilized-metal affinity chromatographies. Ru-binding was confirmed by ESI-MS, and structural integrity was investigated by CD. Results indicate that Ru(tacn)2+ complexes can be bound to surface binding sites in proteins without disruption of structure, opening the door for the study of catalysis in a protein context. 99mTc(CO)3+-binding studies were performed with 3HIU by RP-HPLC. This protein binds Tc+ and resists substitution by free L-histidine, suggesting that peptidic Tc-binding tags could be designed with this approach to readily incorporate the radionuclide into any protein expression system.
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The Interactions of Zinc Thiolate Complexes and Exogenous Metal Species: Investigations of Thiolate Bridging and Metal ExchangeAlmaraz, Elky 2009 May 1900 (has links)
Small molecule Zn(II) complexes containing N- and S- donor environments may
serve as appropriate models for mimicking Zn protein sites, and thus, their reactions
with heavy metal ions such as Pt(II) and W(0) may provide insight into possible adduct
formation and zinc displacement. To study such possible interactions between zinc
finger proteins and platinum-bound DNA, the ZnN2S2 dimeric complex, N,N?-bis(2-
mercaptoethyl)-1,4-diazacycloheptane zinc (II), [Zn-1?]2, has been examined for Znbound
thiolate reactivity in the presence of Pt(II) nitrogen ? rich compounds. The
reactions yielded Zn/Pt di- and tri- nuclear thiolate-bridged adducts and metalexchanged
products, which were initially observed via ESI-mass spectrometry (ESI-MS)
analysis of reaction solutions, and ultimately verified by comparison to the ESI-MS
analysis, 195Pt NMR spectroscopy, and X-ray crystallography of directly synthesized
complexes. The isolation of Zn-(?-SR)-Pt-bridged [(Zn(bme-dach)Cl)(Pt(dien))]Cl
adduct from these studies is, to our knowledge, the first Zn-Pt bimetallic thiolatebridged
model demonstrating the interaction between Zn-bound thiolates and Pt(II). Additional derivatives involving Pd(II) and Au(III) have been explored to parallel the
experiments executed with Pt(II).
The [Zn-1?]2 was then modified by cleavage with Na+[ICH2CO2]- to produce (N-
(3-Thiabutyl)-N?-(3-thiapentaneoate)-1,4-diazacycloheptane) zinc(II), Zn-1?-Ac or
ZnN2SS?O, and 1,4-diazacycloheptane-1,4-diylbis(3-thiapentanoato) zinc(II), Zn-1?-Ac2
or ZnN2S?2O2, monomeric complexes (where S = thiolate, S? = thioether). The [Zn-1?]2
di- and Zn-1?-Ac mono-thiolato complexes demonstrated reactivity towards labile-ligand
tungsten carbonyl species, (THF)W(CO)5 and (pip)2W(CO)4, to yield, respectively, the
[(Zn-1?-Cl)W(CO)4]- complex and the [(Zn-1?-Ac)W(CO)5]x coordination polymer.
With the aid of CO ligands for IR spectral monitoring, the products were isolated and
characterized spectroscopically, as well as by X-ray diffraction and elemental analysis.
To examine the potential for zinc complexes (or zinc-templated ligands) to
possibly serve as a toxic metal remediation agents, Zn-1?-Ac and Zn-1?-Ac2 were reacted
with Ni(BF4)2. The formation of Zn/Ni exchanged products confirmed the capability of
?free? Ni(II) to displace Zn(II) within the N-, S-, and O- chelate environment. The
Zn/Ni exchanged complexes were analyzed by ESI-MS, UV-visible spectroscopy, IR
spectroscopy of the acetate regions, and X-ray crystallography. They serve as
foundation molecules for more noxious metal exchange / zinc displacement products.
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