An Autoinhibited Conformation of LGN Reveals a Distinct Interaction Mode between GoLoco Motifs and TPR Motifs

摘要

LGN plays essential roles in asymmetric cell divisions via its N-terminal TPR-motif-mediated binding to mInsc and NuMA. This scaffolding activity requires the release of the autoinhibited conformation of LGN by binding of Gai to its C-terminal GoLoco (GL) motifs. The interaction between the GL and TPR motifs of LGN represents a distinct GL/target binding mode with an unknown mechanism. Here, we show that two consecutive GL motifs of LGN form a minimal TPR-motif-binding unit. GL12 and GL34 bind to TPR0–3 and TPR4–7, respectively. The crystal structure of a truncated LGN reveals that GL34 forms a pair of parallel a helices and binds to the concave surface of TPR4–7, thereby preventing LGN from binding to other targets. Importantly, the GLs bind to TPR motifs with a mode distinct from that observed in the GL/Gai$GDP complexes. Our results also indicate that multiple and orphan GL motif proteins likely respond to G proteins with distinct mechanisms.