Link proteins

The leucine zipper DNA-binding proteins, described in Chapter 10, are examples of globular proteins that use coiled coils to form both homo- and heterodimers. A variety of fibrous proteins also have heptad repeats in their sequences and use coiled coils to form oligomers, mainly dimers and trimers. Among these are myosin, fibrinogen, actin cross-linking proteins such as spectrin and dystrophin as well as the intermediate filament proteins keratin, vimentin, desmin, and neurofilament proteins. 

T Induction of transglutamina.se, an enzyme that cross-links proteins through (7-g]utamyl)lysine bonds and presumably contributes to the formation of membrane-bound apoptosis bodie.s. 

Peptides derived from disnlfide-linked protein fragments... 

Certain proteins are found to be covalently linked to lipid molecules. For many of these proteins, covalent attachment of lipid is required for association with a membrane. The lipid moieties can insert into the membrane bilayer, effectively anchoring their linked proteins to the membrane. Some proteins with covalently linked lipid normally behave as soluble proteins others are integral... 

Hyaluronic acid y binding domain (link-protein like)... 

GPI-anchored proteins constitute a quite diverse family of cell-surface molecules that participate in such processes as nutrient uptake, cell adhesion, and membrane signaling events [3]. All GPI-linked proteins are destined for the cell surface via trafficking through the secretory pathway, where they acquire the... 

Roche O, Kiyama R, Brooks CL 3rd. Ligand-protein database linking protein-ligand complex strnctnres to binding data. J Med Chem 2001 44 3592-8. 

Complement is not a single protein but comprises a group of functionally linked proteins that interact with each other to provide mar of the effector functions of humoral immunity and inflammation. Most of the components of the system are present in the serum as proenzymes, i.e. enzyme precursors. Activation of a complement molecule occurs as a result of proteolytic cleavage of the molecule, which in itself confers proteolytic activity on the molecule. Thus, many components of the system serve as the substrate of a prior component and, in turn, activate a subsequent component. This pattern of sequential activation results in the system being called the complement cascade. ... 

Wienkoop, S., Glinski, M., Tanaka, N., Tolstikov, V.V., Fiehn, O., Weckwerth, W. (2004). Linking protein fractionation with multidimensional monolithic reversed-phase peptide chromatography/mass spectrometry enhances protein identification from complex mixtures even in the presence of abundant proteins. Rapid Commun. Mass Spectrom. 18, 643-650. 

Figure 15.3 (a) Heat absorption in solutions of native RNase A (trace 1) and RNase A kept in 10% buffered formalin for 2 days (trace 2) and 6 days (trace 3) at pH 7.4 and 23°C. All samples were dialyzed against 75 mM potassium phosphate buffer (pH 7.4) prior to DSC. (b) Dependence of Td of the dialyzed RNase A samples on time of incubation in 10% buffered formalin at pH 7.4 and 23°C. (c) Heat absorption of solutions of formalin-treated RNase A fractions isolated by size-exclusion gel chromatography monomer (trace 1), dimmer (trace 2), and a mixture of oligomers with >5 cross-linked proteins (trace 3). Protein concentrations were 0.5 mg/mL. The thermal denaturation transition temperature (Td) is defined as the temperature of the maximum in the excess heat absorption trace associated with the protein s endothermic denaturation transition. See Rait et al.10 for details. 

Figure 15.4 SDS-PAGE of formalin-treated RNase A fractions taken before (lanes 1-3) and after (lanes 4-6) the DSC scans shown in Figure 15.3c. Lanes 1 and 4, monomer lanes 2 and 5, dimer lanes 3 and 6, mixture of oligomers with >5 cross-linked proteins M, molecular mass markers as in Figure 15.2. See Rait et al.10 for details.

Figure 15.9 The results of capture ELISA on native RNase A and formalin-treated RNase A. Right panel, native RNase A (curve 1) and unfractionated formalin-treated RNase A (curve 2). Left panel, individual fractions of formalin-treated RNase A monomer (curve 3), dimmer (curve 4), trimer (curve 5), tetramer (curve 6), and a mixture of oligomers with >5 cross-linked proteins (curve 7). The ELISA plate wells were coated with monoclonal antibody against bovine pancreatic RNase A (1 pg/mL) overnight at 4°C and then blocked with bovine serum albumin. The wells were incubated for lh at 37°C in the presence of various concentrations of antigen in lOOpL of PBS. After washing, each plate well received a 1 4000 dilution of horseradish peroxidase conjugated rabbit polyclonal anti-RNase A antibody followed by incubation at ambient temperature for lh. After washing, detection was achieved using a mixture of 2,2,-azino-di-(3-ethylbenzthiazoline-6-sulphonate) and hydrogen peroxide. Absorbance was monitored at 405 nm. See Rait etal.11 for details.

Guerrero C, Tagwerker C, Kaiser P, et al. An integrated mass spectrometry-based proteomic approach quantitative analysis of tandem affinity-purified in vivo cross-linked protein complexes (QTAX) to decipher the 26 S proteasome-interacting network. Mol. Cell. Proteomics. 2006 5 366-378. 

Cross-linked proteins through amide bond formation... 

Delgado, C., Francis, G.F., and Fisher, D. (1992) The uses and properties of PEG-linked proteins. Grit. Rev. Ther. Drug Carrier Syst. 9, 249-304. 

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