In situ thermal denaturation of myofibre sub-type proteins studied by immunohistofluorescence and synchrotron radiation FT-IR microspectroscopy

The thermal denaturation of proteins in skeletal muscle was studied and characterised for the first time taking into account the in situ metabolic and contractile fibre types. From serial histological sections, collagen, elastin, various type I, IIa and IIx fibres and type I–IIa and IIa–IIx hybrids were identified by immunohistofluorescence. Histological sections were incubated in buffer solutions at increasing temperatures (40, 50, 60, 70 and 80 °C). Protein secondary structure was investigated by synchrotron radiation FT-IR microspectroscopy on connective tissue and in muscle fibres rigorously identified for sub-type. Whatever the target protein components, increasing temperature resulted in a decrease in α-helix secondary structure and an increase in β-sheet structure. This phenomenon was more pronounced for intracellular proteins than for connective tissue. Although hybrid fibres were generally somewhat less sensitive to unfolding than the pure types, the amplitude of the thermal denaturation of intracellular proteins was practically independent of fibre type.