The Structural and Functional Characterization of the Periplakin Linker Domain

Abstract

Desmosomes are large, complex protein assemblies which, at the most fundamental level, facilitate cellular adhesion. On a grander scale, desmosomes, and more specifically desmosomal networks, are critical for the maintenance of tissue integrity. They link the cytoskeletons of adjacent cells through a vast array of dynamic, multivalent interactions which ultimately equip tissues with the ability to withstand mechanical stress. The interactions of desmosomal proteins between cells in the extracellular space are quite well characterized. On the intracellular space, the story becomes much more complex as a plethora protein families and their constitutive members assemble in a tissue specific, multivalent fashion to create a mature desmosome. The plakin proteins facilitate the final connection between the desmosome and the cytoskeleton of each cell, thereby establishing the network of cytoskeletal connectivity throughout a given tissue. This connections between the desmosome and the cytoskeleton have been historically mapped to C-terminal plakin repeat domains (PRDs) of the plakin proteins. However, each member of the plakin family has a linker domain while not all plakins have PRDs. This implies some distinct functionality of these linker domains. Moreover, the linker domain of periplakin has been identified as a site for phosphorylation, which has been previously linked to the dynamic assembly and disassembly of desmosomes. This work seeks to elucidate the functional role of the periplakin linker domain by combining structural nuclear magnetic resonance spectroscopy (NMR) and small-angle x-ray scattering (SAXS) analysis, with quantitative binding analysis using MicroScale Thermophoresis (MST). By performing phosphomimic mutagenesis, we also gain insight into the effects of the aforementioned phosphorylation on the function of this domain.