Heat-induced denaturation/aggregation of porcine plasma and its fractions studied by FTIR spectroscopy

The aim of the present work is the in depth study of the protein aggregation mechanisms of whole porcine plasma and its fractions (serum, albumin and globulins) during heating using FTIR spectroscopy. Also, 2D correlation spectroscopy (2D COS) was used to establish the sequence of events during heat-induced gelation for all fractions. The results indicate that serum albumin quickly aggregates from 70 °C through non-native intramolecular β-sheets while globulins show lower susceptibility to protein aggregation. When found together, the aggregation pattern strongly depends on the composition of the protein mixture. That makes the great difference between plasma (serum albumin + globulins + fibrinogen) and serum (serum albumin + globulins) behavior, with the aggregation degree at the end of the thermal process being enhanced in the presence of fibrinogen – and achieving a similar level to that of serum albumin – while minimized in its absence. Attending on the low content of fibrinogen in plasma, our results suggest a great fibrinogen ability to alter the thermal serum albumin and globulins behavior by modifying the negative interactions established between them when no more proteins are found in the media. Moreover, it is noteworthy the slow plasma aggregation pattern at the beginning of the thermal process relative to serum albumin, this way allowing a higher protein unfolding. This could be related to the high heat-induced gel properties of plasma. Also, 2D COS indicates that the sequence of events is very similar for the all analyzed samples, with α-helix being more thermo-labile than native β-sheet structure.

Deconvoluted infrared spectra in the amide I′ absorption region upon of plasma solution (6% w/v of protein in D2O) from 30 to 90 °C at pH 7.5 (a) and the corresponding 2D IR synchronous (b) and asynchronous (c) maps. Figure optionsDownload as PowerPoint slideHighlights
► We study the protein aggregation through intermolecular β-sheet of porcine plasma during heating.
► FTIR spectroscopy has been the used technology.
► Plasma protein fractions have also been analyzed to understand its importance on gel properties.
► The aggregation rate appears strongly dependent on the composition of the protein mixture.
► However, at any case a-helix is shown as more thermo-labile than native β-sheet structure.