Dynein light chain LC8 promotes assembly of the coiled-coil domain of swallow protein

LC8 is a highly conserved light-chain subunit of cytoplasmic dynein that is thought to play a fundamental role in both the assembly of the motor complex and the recruitment of cargo. An interaction between LC8 and the Drosophila protein swallow has been previously characterized and supports a role for dynein in the localization of maternal morphogens during oogenesis. Swallow is required for the proper localization of bicoid mRNA, the anterior determinant that plays a critical role in establishment of the Drosophila embryonic axis. In this work, we prepared constructs of swallow, each containing a predicted coiled-coil domain and variable surrounding segments that lie within the domain proposed to interact with LC8. The interaction between LC8 and swallow domains was characterized by glutathione S-transferase (GST) pull-down assays, limited proteolysis followed by mass spectrometry, and circular dichroic spectroscopy. Hydrodynamic measurements, covalent cross-linking, and circular dichroic spectroscopy show that this domain of swallow is an unstable dimeric coiled-coil. Upon LC8 binding, however, the coiled-coil becomes significantly more stable. A possible general role for LC8 in macromolecular assembly is discussed.