Proteins polymerization

Figure 1 Stages of amyloid aggregation steps in protein polymerization and the techniques used to measure them for the Alzheimer s [ peptide.

Lansbury PT Jr. Yeast prions inheritance by seeded protein polymerization Curr Biol 1997 7 R617-R619. 

Carbodiimide coupling to carboxylate-containing QDs usually involves the use of EDC in a single-step or two-step process to form an amide bond. If a one-step reaction is done, the QD is activated with EDC in the presence of an amine-containing molecule, such as a protein. Many protocols use this method, but it can result in protein polymerization in addition to coupling, because proteins contain both carboxylates and amines. A two-step protocol results in better control of the reaction (Figure 9.61). In the first step, EDC is used in the presence of sulfo-NHS to activate the carboxylates on the particles to intermediate sulfo-NHS esters. After a quick separation step to remove excess reactants, the activated QDs are added to the protein solution to be coupled. This then results in amide bond formation without polymerization of the protein in solution. See Chapter 3, Section 1 and Chapter 14, Section 1 for additional information on this process. 

QD nanoparticles containing carboxylate groups also may be reacted in a two-step EDC/ sulfo-NHS reaction to couple proteins and other molecules containing both amines and car-boxylates. This type of reaction is designed to remove excess EDC activating agent before addition of protein, so protein polymerization cannot occur. 

Also see Protein Polymerization Self-Assembly Mechanisms. 

F. Oosawa S. Asakura (1975) Thermodynamics of Protein Polymerization, Academic Press, New York. 

The threshold concentration of monomer that must be exceeded for any observable polymer formation in a self-assembling system. In the context of Oosawa s condensation-equilibrium model for protein polymerization, the cooperativity of nucleation and the intrinsic thermodynamic instability of nuclei contribute to the sudden onset of polymer formation as the monomer concentration reaches and exceeds the critical concentration. Condensation-equilibrium processes that exhibit critical concentration behavior in vitro include F-actin formation from G-actin, microtubule self-assembly from tubulin, and fibril formation from amyloid P protein. Critical concentration behavior will also occur in indefinite isodesmic polymerization reactions that involve a stable template. One example is the elongation of microtubules from centrosomes, basal bodies, or axonemes. 

The generality of the end-wise depolymerization kinetic model is indicated by the comparison of the observed and predicted time-courses of cold-induced microtubule disassembly (Fig. 3). See Self-Assembly Protein Polymerization... 

Any polymerization reaction in which the product of each elongation step can itself also undergo further polymerization. When the same types of bonds and/or conformational states that are present in the reactant(s) are generated within product(s) during elongation, the process is referred to as isodesmic polymerization. Such is the case for the indefinite polymerization of actin, tubulin, hemoglobin S, and tobacco mosaic virus coat protein. See Nudeation Protein Polymerization Actin Assembly Kinetics Microtubule Assembly Kinetics Microtubule Assembly Kinetics... 

Turbidity has proven to be especially useful in studies of protein polymerization, where one can demonstrate that the turbidity is directly proportional to the polymer mass concentration. This is illustrated in the following plot (Fig. 1) obtained for assembled microtubules. 

PROTEIN POLYMERIZATION ACTIN ASSEMBLY KINETICS MICROTUBULE ASSEMBLY KINETICS... 

ACTIN ASSEMBLY KINETICS MICROTUBULE ASSEMBLY KINETICS PROTEIN POLYMERIZATION KINETICS NUCLEIC ACID RENATURATION KINETICS Nucleic acid structure,... 

Stuurman N, Sasse B, Fisher PA. 1996. Intermediate filament protein polymerization Molecular analysis of Drosophila nuclear lamin head-to-tail binding. J Struct Biol 117 1-15. 

Figure 10.5 The equilibrium monomer concentration as a function of the total monomers for a nucleation-elongation protein polymerization process described by Equations (10.7) and (10.13). The constant K = k+ /K is the association constant of a monomer to the polymer [A ]eq is the equilibrium free monomer concentration and A is the total monomer concentration. The variable a = 1 — K /K depends on the difference in equilibrium constants between elongation and nucleation steps. At a = 0 there is no difference in equilibrium constants at er = l nucleation is highly unfavorable compared to elongation and there is infinite cooperativity in the polymerization process.

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