Determination of the equilibrium constants of associating protein systems. IV. The application of the weight-average partition coefficient to analysis of BM1 nonideality term (as applied to bovine liver L-glutamate dehydrogenase)

HIV Rev self-assembly is linked to a molten-globule to compact structural transition

By regulating the differential expression of proviral pre mRNA in the host cell, Rev plays a crucial role in the HIV-1 life cycle. The capacity of Rev to function is intimately linked to its ability to self-associate. Nevertheless, little is known about the exact role of self-association in the molecular mechanism defining its biological activity. A prerequisite knowledge is a definition of the molecular events undertaken by Rev during the process of self-assembly. Thus, this study was initiated to monitor the structure of Rev as a function of protein concentration. Rev undergoes a structural transition as a consequence of self-assembly. This structural transition was monitored by three spectroscopic methods. The accessibility of the single tryptophan in Rev monomer to acrylamide quenching increases with decreasing protein concentration. At very low concentration of Rev, the tryptophan accessibility is close to that of an unfolded Rev. As evaluated by circular dichroism, the secondary structure of Rev is protein concentration dependent as evidenced by an increase in the magnitude of ellipticity with increasing protein concentration. Further, results from ANS binding studies indicate that the ANS binding sites in Rev experience an apparent increase in hydrophobicity as the Rev concentration was increased. These concentration dependent changes seem to reach a maximum above 5 microM Rev monomer concentration. In order to define the mode of Rev self-association sedimentation velocity and equilibrium experiments were conducted. There are evidently two consecutive progressive association processes. At protein concentrations below 0.5 mg/ml, the data from sedimentation studies can be fitted to a single isodesmic model. Simulation of velocity sedimentation profile indicates that free Rev monomer that has not entered into the association processes can best be described to exhibit a value of S(20,w) that is substantially smaller than 1.4 S, a value needed to fit the rest of the data. The latter value is consistent for a Rev monomer with the expected molecules weight and if it were to assume a compact globular shape. These spectroscopic and hydrodynamic results imply that monomeric Rev is in a molten globule state, which becomes more compact upon self-association.

Stoichiometry of the vinblastine-induced self-association of calf brain tubulin

The self-association of calf brain tubulin in PG buffer (10(-2) M NaPi and 10(-4) M GTP, pH 7.0) induced by the antimitotic drug vinblastine has been investigated by velocity sedimentation. Schlieren sedimentation patterns were examined at low vinblastine concentrations where the boundary resolves into a bimodal one and at high vinblastine concentration where a single forward-skewed peak prevails. Weight-average sedimentation coefficients of tubulin were determined as a function of protein concentration, the results fitting well a self-association model of an idefinite isodesmic mechanism. This was confirmed by computer simulation of the sedimentation boundary profiles.

Thermodynamic compensation process in interacting protein systems: definition of thermodynamic compensatory temperature, (Tc)

In our thermodynamic analysis of the non-linear Van't Hoff expression as applied to several self-associating systems -- specifically in the cases of bovine liver L-glutamate dehydrogenase (GDH), glucagon and S-carboxymethylated apo A-II protein from human high density lipoprotein -- we have examined the interrelationships of a number of thermodynamic temperatures as they affect the association process. We found the principal determinants of the linear thermodynamic compensation process to be delta S0(T)/delta C0p(T) = (delta T'C)/(Texp), where (delta T'C) = Texp). We have defined the unique compensatory temperature, (TC), for any interacting system, at which the contributions of enthalpy and entropy to the association process are balanced.

Determination of the equilibrium constants of self-associating protein systems. XI. The application of C-(r) in graphical analysis and the enumeration of interacting species in the ultracentrifuge

A greatly simplified procedure is proposed which employs C equals f(r) as determined from sedimentation equilibrium measurements in graphical analysis of self-associating protein systems and in the enumeration of interacting species in the ultracentrifuge. Basic equations given here are applicable to any self-associating system. A procedure is outlined for enumeration of interacting components independent of non-ideal behavior, using principal component analysis.

Rates of GDP-induced and GTP-induced depolymerization of glutamate dehydrogenase: a possible factor in metabolic regulation

The rate of the depolymerization of beef liver glutamate dehydrogenase induced by coenzyme and the purine nucleotides guanosine 5'-diphosphate and guanosine 5'-triphosphate, which are potent inhibitors of enzymatic activity, has been measured by rapid light scattering techniques and by absorbancy changes with stop flow. It is shown that the rate constant for this process may vary from several milliseconds to several seconds depending upon the nucleotides used. The widely varying rate constants for the nucleotide-induced depolymerization may serve a role in determining the nature of the regulation of enzyme activity by nucleotides. Depolymerization induced by guanosine 5'-diphosphate in the presence of diphosphopyridine nucleotide is slower than in the presence of triphosphopyridine nucleotide as coenzyme, and this difference is apparently due to the isomerization of the enzyme as a result of diphosphopyridine nucleotide binding to a second, nonactive site. This binding, as well as binding of the coenzyme to the active site, may be conveniently measured by a purine nucleotide-induced spectral shift in the coenzyme absorption spectrum. It is also shown that complete depolymerization of the enzyme in the presence of guanosine 5'-triphosphate is accomplished by about half saturation of the coenzyme active sites (6-8 active "monomer").