GoLoco motif (GL)-containing proteins regulate G-protein signaling by binding to Gα subunit and acting as guanine nucleotide dissociation inhibitors (GDI). GLs of LGN are also known to tether its N-terminal TPR repeats targets (e.g. NuMA and mInsc) to cell cortex via binding to membrane bound Gα_i/o during asymmetric cell division. The molecular basis underlying both G-protein signaling and scaffolding roles of LGN GLs is unclear. Here, we show that each of the four GLs of LGN binds to Gα_i⋅GDP independently and with comparable affinities (K_D ~100 nM). The crystal structures of Gα_i⋅GDP in complex with LGN GL3 and GL4 peptides, respectively, reveal distinct GL/Gα_i interaction features when compared to the only known GL/Gα_i interaction between RGS14 and Gα_i1: only a few residues C-t...[ Read more ]

GoLoco motif (GL)-containing proteins regulate G-protein signaling by binding to Gα subunit and acting as guanine nucleotide dissociation inhibitors (GDI). GLs of LGN are also known to tether its N-terminal TPR repeats targets (e.g. NuMA and mInsc) to cell cortex via binding to membrane bound Gα_i/o during asymmetric cell division. The molecular basis underlying both G-protein signaling and scaffolding roles of LGN GLs is unclear. Here, we show that each of the four GLs of LGN binds to Gα_i⋅GDP independently and with comparable affinities (K_D ~100 nM). The crystal structures of Gα_i⋅GDP in complex with LGN GL3 and GL4 peptides, respectively, reveal distinct GL/Gα_i interaction features when compared to the only known GL/Gα_i interaction between RGS14 and Gα_i1: only a few residues C-terminal to the conserved GL motif sequence are required for LGN GLs to bind to Gα_i⋅GDP; the C-terminal part of LGN GL peptide occupies a much smaller surface area on the helical-domain of Gα_i in contrast to that occupied by the RGS14 GL; a highly conserved double Arg-finger sequence (“R-Ψ-D/E-D/E-Q-R”) is responsible for LGN GL/Gα_i recognition. We demonstrate that the LGN GL/Gα_i interaction represents a general binding mode between GL motifs and Gα_i. Finally, we show that the LGN GL motifs are potent GDIs. Thus the GLs of LGN may function both as the Gα/LGN/NuMA/mInsc complex scaffold and a Gα signaling regulator during asymmetric cell division.