Multiple Recognition Motifs Provide Rigidity to Stabilize LC8 Complexes

Abstract

Hub proteins have a large number of interacting partners and are of special importance in organizing protein-protein networks. LC8, a 10 kDa dimeric component of the cytoplasmic dynein biological motor complex has a relatively large number of interacting partners and fits the description of a hub. Partner proteins of LC8 include the intermediate chain (IC) subunit of cytoplasmic dynein, Chica, a mitotic spindle-associated protein, Nup159, a component of the yeast nuclear pore complex, and a wide array of proteins with roles in apoptosis, enzyme regulation and viral pathogenesis. Linear motifs mediate binding between LC8 and its partner proteins, but while partner proteins such as dynein IC have only one recognition motif, others such as Chica and Nup159 are enriched with multiple interacting motifs.To better understand the importance of multiple recognition motifs in the LC8 interaction network, we have initiated structural and thermodynamic studies of the LC8/Chica and LC8/Nup159 complexes. Chica and Nup159 have four and six putative recognition motifs respectively, nestled within segments that are intrinsically disordered. Our results indicate that LC8 forms a dynamic complex with both proteins, binding only three (Chica) or five (Nup159) of the putative recognition motifs. Furthermore, we show that only three LC8 dimers are needed for optimal stability of the Nup159/LC8 complex, and suggest that the evolutionary adaptation of multiple LC8 recognition motifs imparts to the complex other properties such as rigidity. These findings extend the repertoire of functions of intrinsically disordered proteins to fine-tuning and versatile assembly of higher order macromolecular complexes.