Linking polypeptides

Interestingly, one can use a Cys-Gly-Gly linker at the N- or C-terminal of the polypeptide chain in the design of disulfide-bridged coiled coils. The advantage of this approach is that the Cys-Gly-Gly linker allows complete flexibility of the polypeptide chains to adopt their most stable conformation, which includes different oligomerization states, while maintaining the polypeptide chains in a parallel manner. 49 In addition, the Cys-Gly-Gly linker eliminates the monomer-dimer equilibrium and the peptide concentration effect on stability, which is observed in two-stranded coiled-coil formation of noncovalent linked polypeptides. 49 861... 

The assembly of an N-terminal cross-linked polypeptide is shown in Scheme 14.[821 The assembly of a polypeptide with both C-terminal and N-terminal links, built up from residues shown in Scheme 15, is shown in Scheme 16.[831... 

The term quaternary structure was proposed to supplement the terms primary, secondary, and tertiary structure, 9 and refers to the spatial arrangement of noncovalently linked polypeptides which we shall call subunits. Generally, a subunit is defined as a tertiary structural unit composed of a single polypeptide, but the definition is somewhat ambiguous. In aspartate transcarbamoylase from Escherichia coli, for example, tertiary structural units composed of three catalytic polypeptide chains are called catalytic subunits and those composed of two regulatory chains are called regulatory subunits.2)... 

The IL-2 receptors are composed of three noncovalently linked polypeptide chains a, (3, and y. These chains (or their complex) form the basis for three kinds of IL-2 receptors ... 

Information is incomplete concerning the three-dimensional structure of IL-12. However, it is known to be a heterodimeric four a-helical short-chain cytokine (196AA/306AA) that stimulates T- and NK-cell function. It consists of two covalently linked polypeptide chains, one of 35kDa (p35, IL-12a) and the other of 40kDa (p40, IL-12P). The p35 chain has a four a-helix structure, similar to that of many other cytokines, but the p40 chain of... 

Fig. 5. Model for the protein binding site for protoheme in cytochrome b559 (A) and modei for the orientation of the two histidine imidazole rings in cytochrome bS59 (B). See text for discussion. Figures adapted from Babcock, Widger, Cramer, Oertling and Metz (1985) Axial ligands of chloroplast cytochrome b559 identification and requirement for a heme-cross-linked polypeptide structure. Biochemistry 24 3643.

Polymers with intramolecular cross-links have organized spatial structures, and are good models for the tertiary structure of proteins (26,27,1 ). In the studies discussed here poly Glu52Lys33Tyr15 (No. 3) was internally cross-linked with Woodward s reagent K or ionic carbodiimide and fractionated on Sephadex G-100. The number of cross-links in each fraction was determined by amino acid analysis. In addition, the parent polymer was fractionated in the same way to provide standards for comparison with the cross-linked polypeptides. 

Describe the additional steps that must be used for sequencing disulfide-linked polypeptides and oligomeric proteins. 

Rowland LP, Shneider NA (2001) Amyotrophic lateral sclerosis. N Engl J Med 344 1688-1700 Sadqi M, Hernandez F, Pan U, Perez M, Schaeberle MD, Avila J, Munoz V (2002) Alpha-helix structure in Alzheimer s disease aggregates of tau-protein. Biochemistry 41 7150-7155 Sanchez de Groot N, Pallares 1, Aviles FX, Vendrell J, Ventura S (2005) Prediction of hot spots of aggregation in disease-linked polypeptides. BMC Struct Biol 5 18 Sasaki T, Kaiser ET (1989) HeUchrome synthesis and enzymic activity of a designed hemeprotein. J Am ChemSoc 111 380-381... 

Chrisman, P.A. Pitteri, S.J. Hogan, J.M. McLuckey, S.A. SOj electron transfer ion/ion reactions with disulfide linked polypeptide ions. J. Am. Soc. Mass Spectrom. 2005,16, 1020-1030. 

Gunawardena, H.P. Gorenstein, L. Erickson, D.E. Xia, Y. McLuckey, S.A. Electron transfer dissociation of multiply protonated and fixed charge disulfide linked polypeptides. Int. J. Mass Spectrom. 2007, 265,130-138. 

DTSSP(DTSSB) does not induce the formation of A890 oligomers 3)DTSSP (DTSSB) links polypeptides from various pigment-protein complexes, but no links within the limits of one complex are found 4)The formation of links does not lead to stabilization of the native structure of pigment-protein complexes in the assembly A 890. 

FIGURE 4 Model of PS I. The cross-linked polypeptides are indicated with - ... 

Most proteins with molecular weight greater than 50,000 consist of two or more noncova-lently linked polypeptide chains. The arrangement of protein monomers into an aggregation is known as quaternary (4°) structure. A good example is hemoglobin (Figure 18.16), a protein that consists of four separate polypeptide chains two a-chains of 141 amino acids each and two S-chains of 146 amino acids each. 

Class III MHC genes code for a serum protein consisting of three covalently linked polypeptides, known as the a-, P- and Y-chains (AT, 87,000, 78,000 and... 

Binds metal ions and links polypeptide chains via an—CH.S—SCH,— group. Heterocyclic amine base that acts as a nucleophile or binds metal ions. 

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