Cross linking reveals laminin coiled coil architecture
Significance Large, fibrous, and flexible extracellular matrix proteins are integral to development and maintenance of tissues in the body. Laminin is an extracellular matrix component that provides a physical substrate for cell adhesion and induces signaling pathways that maintain cell health and functionality. Despite the physiological importance of laminin, major gaps remain in our understanding of how its three subunits come together to form the characteristic cross shaped laminin structure. Laminin was treated with chemicals that link amino acids close in space, providing a map of the subunit arrangement and correcting previous suppositions made on the basis of amino acid sequence inspection alone. Laminin, an ~800 kDa heterotrimeric protein, is a major functional component of the extracellular matrix, contributing to tissue development and maintenance. The unique architecture of laminin is not currently amenable to determination at high resolution, as its flexible and narrow segments complicate both crystallization and single particle reconstruction by electron microscopy. Therefore, we used cross linking and MS, evaluated using computational methods, to address key questions regarding laminin quaternary structure. This approach was particularly well suited to the ~750 A coiled coil that mediates trimer assembly, and our results support revision of the subunit order typically presented in laminin schematics. Furthermore, information on the subunit register in the coiled coil and cross links to downstream domains provide insights into the self assembly required for interaction with other extracellular matrix and cell surface proteins.
Proceedings of the National Academy of Sciences