Neurofilament Light Protein Rod Domain Exhibits Structural Heterogeneity.

Neurofilaments are neuron-specific proteins that belong to the intermediate filament (IFs) protein family, with the neurofilament light chain protein (NFL) being the most abundant. The IFs structure typically includes a central coiled-coil rod domain comprised of coils 1A, 1B, and 2, separated by linker regions. The thermal stability of the IF molecule plays a crucial role in its ability for self-association. In the current study, we investigated the thermal stability of NFL coiled-coil domains by analyzing a set of recombinant domains and their fusions (NFL 1B , NFL 1A+1B , NFL 2 , NFL 1B+2 , and NFL ROD ) via circular dichroism spectroscopy and differential scanning calorimetry. The thermal stability of coiled-coil domains is evident in a wide range of temperatures, and thermal transition values (T m ) correspond well between isolated coiled-coil domains and full-length NFL. NFL 1B has a T m of 39.4 °C, and its' fusions, NFL 1A+1B and NFL 1B+2 , have a T m of 41.9 °C and 41.5 °C, respectively. However, in the case of NFL 2 , thermal denaturation includes at least two thermal transitions at 37.2 °C and 62.7 °C. These data indicate that the continuous α-helical structure of the coil 2 domain has parts with varied thermal stability. Among all the NFL fragments, only NFL 2 underwent irreversible heat-induced denaturation. Together, these results unveil the origin of full-length NFL's thermal transitions, and reveal its domains structure and properties.