Infrared spectroscopy and ultrasonic velocimetry as a tool for probing conformational flexibility of proteins

Abstract

Because of the crucial importance of structural fluctuations for function and stability of proteins, there is a strong interest for the relationships between structural fluctuations, the parameters of protein denaturation and the kinetics of H/D-exchange. Structural fluctuations can be described by volume and entropy fluctuations and these quantities are accessible via the isothermal compressibility, the thermal expansion and the isobaric heat capacity.

Our aim is to present the principal problem concerning the experimental procedures to answer those questions using lysozyme and α-lactalbumin. Whereas the transition parameters and the kinetics of the H/D-exchange were obtained using FTIR spectroscopy, the adiabatic compressibility was obtained by a combination of ultrasonic velocimetry and densitometry. It could be shown that the stability of the investigated proteins is correlated with reduced volume fluctuations. The expected direct correlation between H/D exchange rates and structural fluctuations could not be seen and it is assumed that the interactions are more complex than from the intuitive point of view.     

Pressure induced changes in proteins studied in the diamond anvil cell with Raman spectroscopy

Abstract

The pressure induced denaturation of serum albumin and lysozyme is studied. Preliminary results suggest that the changes induced in serum albumin are reversible below 10 kbar.     

From Aggregation to Chaperoning: Pressure Effect on Intermolecular Interactions of Proteins

The effect of pressure on the protein aggregation is shown in this paper. Deposition of insoluble protein aggregates is one of the key factors in the conformational diseases. Pressure counteracts the formation of intermolecular g -structure. Already slight pressurization to typically 2-3 kbar can destabilize aggregates of apo-horseradish peroxidase. On the other hand, the chaperone proteins, which prevent aggregation of damaged proteins exist in big oligomers. We show that pressure treatment of these aggregates changes the chaperone activity.     

Molecular aspects of high pressure biology

Abstract

A review is presented of the effect of pressure on the conformation of chymotrypsin, the interaction of ligands with mymoglobin and the pressure induced denaturation in lysozyme and chymotrypsinogen. The implication for biological processes is discussed.     

Spin-seebeck effect: a phonon driven spin distribution

Here we report on measurements of the spin-Seebeck effect in GaMnAs over an extended temperature range alongside the thermal conductivity, specific heat, magnetization, and thermoelectric power. The amplitude of the spin-Seebeck effect in GaMnAs scales with the thermal conductivity of the GaAs substrate and the phonon-drag contribution to the thermoelectric power of the GaMnAs, demonstrating that phonons drive the spin redistribution. A phenomenological model involving phonon-magnon drag explains the spatial and temperature dependence of the measured spin distribution.     

Localization and antilocalization in InSb and InAs antidot lattices

We report on the observation of localization, antilocalization and Altshuler–Aronov–Spivak (AAS) oscillations in antidot lattices patterned on high-mobility InSb/InAlSb and InAs/AlGaSb heterostructures. In addition, the antidot lattices display ballistic commensurability features. The strength of the localization peak in InSb antidot lattices decreases exponentially with temperature, with a high characteristic temperature of 25 K between 0.4 and 50 K. Analysis of the AAS oscillations enables the extraction of phase and spin coherence lengths in InAs.     

Extending the Pressure–Temperature State Diagram of Myoglobin

The pressure–temperature (P,T) diagram of proteins proposed by Hawley concerns the equilibrium between native and denatured forms. However, the importance of protein aggregation is increasingly recognized, and it has been suggested that certain aggregated states represent alternative folds of the polypeptide chain. Here, we present a P,T‐diagram for myoglobin in which we include the aggregated state and suggest to call it a P,T‐state diagram, as not all boundaries are true equilibrium transitions. We observe by Fourier transform infrared spectroscopy that increasing temperature causes the protein to aggregate, but that a subsequent further temperature increase results in the dissociation of this aggregate. Moreover, we observe that moderate pressures stabilize myoglobin against thermal denaturation. We hypothesize that this effect originates from the volume changes associated with the aggregation transition.