Time-resolved FTIR difference spectroscopy as tool for investigating refolding reactions of ribonuclease T1 synchronized with trans --> cis prolyl isomerization

FTIR and nDSC as analytical tools for high-concentration protein formulations

PURPOSE

The aim of the study is to evaluate Fourier-transform infrared spectroscopy (FTIR) as an analytical tool for high-concentrated protein formulations.

METHODS

FTIR is used to determine the melting temperature (T(m (FTIR))) of various proteins, such as bovine serum albumin (BSA), immunoglobulin (IgG1), beta-lactoglobulin (beta-LG), and lysozyme (HEWL), at different protein concentrations (5-100 mg/mL), where four data interpretation methods are discussed. The obtained T(m (FTIR)) values are further compared to the T(m) measured by the nanodifferential scanning calorimetry (nDSC) technique.

RESULTS

The T(m (FTIR)) values of IgG1 and beta-LG showed strong consistency and corresponded to the nDSC results irrespective of the method of data interpretation and the protein concentration applied. In contrast, the T(m (FTIR)) of BSA and HEWL is characterized by significant deviations. Only the midpoint of the second-derivative intensity-temperature curve of the intermolecular beta-sheet mode measured at a concentration of 100 mg/mL is consistent with the nDSC results.

CONCLUSIONS

Determination of a T(m (FTIR)) is feasible by the midpoint of the intensity-temperature plot of the arising intermolecular beta-sheet band. More significant results are obtained for proteins, which are predominantly composed of intramolecular beta-sheet elements as well as at higher protein concentrations. A further study was started to assess the predictability of long-term protein stability by T(m (FTIR)).

Regulation of peptide bond cis/trans isomerization by enzyme catalysis and its implication in physiological processes

In some cases, the slow rotational movement underlying peptide bond cis/trans isomerizations is found to control the biological activity of proteins. Peptide bond cis/trans isomerases as cyclophilins, Fk506-binding proteins, parvulins, and bacterial hsp70 generally assist in the interconversion of the polypeptide substrate cis/trans isomers, and rate acceleration is the dominating mechanism of action in cells. We present evidence disputing the hypothesis that some of the molecular properties of these proteins play an auxiliary role in enzyme function.

Formation of critical oligomers is a key event during conformational transition of recombinant syrian hamster prion protein

We have investigated the conformational transition and aggregation process of recombinant Syrian hamster prion protein (SHaPrP90-232) by Fourier transform infrared spectroscopy, circular dichroism spectroscopy, light scattering, and electron microscopy under equilibrium and kinetic conditions. SHaPrP90-232 showed an infrared absorbance spectrum typical of proteins with a predominant alpha-helical structure both at pH 7.0 and at pH 4.2 in the absence of guanidine hydrochloride. At pH 4.2 and destabilizing conditions (0.3-2 m guanidine hydrochloride), the secondary structure of SHaPrP90-232 was transformed to a strongly hydrogen-bonded, most probably intermolecularly arranged antiparallel beta-sheet structure as indicated by dominant amide I band components at 1620 and 1691 cm-1. Kinetic analysis of the transition process showed that the decrease in alpha-helical structures and the increase in beta-sheet structures occurred concomitantly according to a bimolecular reaction. However, the concentration dependence of the corresponding rate constant pointed to an apparent third order reaction. No beta-sheet structure was formed within the dead time (190 ms) of the infrared experiments. Light scattering measurements revealed that the structural transition of SHaPrP90-232 was accompanied by formation of oligomers, whose size was linearly dependent on protein concentration. Extrapolation to zero protein concentration yielded octamers as the smallest oligomers, which are considered as "critical oligomers." The small oligomers showed spherical and annular shapes in electron micrographs. Critical oligomers seem to play a key role during the transition and aggregation process of SHaPrP90-232. A new model for the structural transition and aggregation process of the prion protein is described.