Metals binding to protein

Copper is an essential element. It is of a great importance in the metabolic processes of plants, its content in plant tissues being very low, much lower than those of zinc and manganese. Copper ions form complexes with proteins and with the other biopolymers in plant tissues. These complexes are more stable than those of the other metals. Binding to proteins enhances the catalytic activity of copper. Copper participates in many oxidation-reduction enzymatic systems, and it is thus of importance particularly in respiration and photosynthesis processes. In plants it is also essential in the nitrogen metabolism. Its concentration in plants ranges... 

Chasteen ND, DeKoch RJ, Rogers BL, Hanna MW. 1973. Use of the vanadyl(IV) ion as a new spectroscopic probe of metal binding to proteins vanadyl insulin. J Am Chem Soc 95 1301-1309. 

Blue copper proteins. A typical blue copper redox protein contains a single copper atom in a distorted tetrahedral environment. Copper performs the redox function of the protein by cycling between Cu and Cu. Usually the metal binds to two N atoms and two S atoms through a methionine, a cysteine, and two histidines. An example is plastocyanin, shown in Figure 20-29Z>. As their name implies, these molecules have a beautiful deep blue color that is attributed to photon-induced charge transfer from the sulfur atom of cysteine to the copper cation center. 

Dietary copper also appears to be antagonistic to the adverse effects of lead on the hematopoietic system, growth depression, and tissue hypertrophy (Klauder and Peterini 1975). The reduction in uptake of lead and decrease of lead-induced ALAD inhibition upon administration of copper may be achieved through a competition between the two metals for binding to proteins (Underwood 1977). 

On the other hand, many substrates and inhibitors bind to protein-bound metals by the formation of such rings. 

Many metals bind to the sulfur of sulfhydryl groups in proteins. Metals that bind sulfur in preference to oxygen not only form strong cr bonds with the readily polarizable ligands, but also tt bonds by back-donation of electrons from metal drr to ligand dir orpir orbitals. The electronegativity... 

An analysis of metal binding to peptide carbonyl groups (Chakrabarti, 1990), mainly calcium ions in protein crystal structures, shows that the cations tend to lie in the peptide plane near the C=0 bond direction. Generally, this binding occurs in turns in proteins or in regions with no regular secondary structures. Ca---0 distances range from 2.2 to 2.5 A, and metal ions do not deviate by more than 35° from the peptide plane. Thus, metal ions in proteins do not, Chakrabarti observed, bind in lone-pair directions. 

The engineering of zinc-binding sites in a-helical peptides, where metal binding stabilizes protein tertiary structure, has been reported by Handel and DeGrado (1990). In these experiments zinc-binding sites are incorporated into a dimeric helix-loop—helix peptide (H3 2) and a protein composed of four helices connected by three short loop sequences (H3 4). a model of one subunit of the H3 2 dimer is found in Fig. 47. In addition to metal complexation by two histidine residues at positions n and n+4 of one a helix, the metal is coordinated by a third histidine residue of an adjacent a helix. The composition of the zinc coordination polyhedron is like that of carbonic anhydrase (i.e., Hiss), and spectroscopic results suggest that all three histidine residues are involved in zinc complexation. This work sets an important foundation... 

Ca2+ binding to proteins is generally considered to be weak relative to that of the transition metal ions. As is predictable for a hard metal ion the coordination appears to be entirely through O donor atoms, from carboxyl and peptide O atoms (see Table 11). Unfortunately Ca2+ is spectroscopically silent and much of the work on the elucidation of its binding sites relies upon the specific... 

Vanadate transport in the erythrocyte was shown to occur via facilitated diffusion in erythrocyte membranes and was inhibited by 4,4 -diisothiocyanostilbene-2,2 -disulfonic acid (DIDS), a specific inhibitor of the band 3 anion transport protein [23], Vanadium is also believed to enter cells as the vanadyl ion, presumably through cationic facilitated diffusion systems. The divalent metal transporter 1 protein (called DMT1, and also known as Nramp2), which carries iron into cells in the gastrointestinal system and out of endosomes in the transferrin cycle [24], has been proposed to also transport the vanadyl cation. In animal systems, specific transport protein systems facilitate the transport of vanadium across membranes into the cell and between cellular compartments, whereas the transport of vanadium through fluids in the organism occurs via binding to proteins that may not be specific to vanadium. 

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