Lis1 promotes the formation of maximally activated cytoplasmic dynein-1 complexes

Abstract

Cytoplasmic dynein-1 is a molecular motor that drives nearly all minus-end-directed microtubule-based transport in human cells, performing functions ranging from retrograde axonal transport to mitotic spindle assembly1,2. Activated dynein complexes consist of one or two dynein dimers, the dynactin complex, and an \"activating adaptor\", with maximal velocity seen with two dimers present (Fig. 1a)3-6. Little is known about how this massive [~]4MDa complex is assembled. Using purified recombinant human proteins, we uncovered a novel role for the dynein-binding protein, Lis1, in the formation of fully activated dynein complexes containing two dynein dimers. Lis1 is required for maximal velocity of complexes activated by proteins representing three different families of activating adaptors: BicD2, Hook3, and Ninl. Once activated dynein complexes have formed, they do not require the presence of Lis1 for sustained maximal velocity. Using cryo-electron microscopy we show that human Lis1 binds to dynein at two sites on dyneins motor domain, similar to yeast dynein7. We propose that the ability of Lis1 to bind at these sites may function in multiple stages of assembling the motile human dynein/ dynactin/ activating adaptor complex.\n\nO_FIG O_LINKSMALLFIG WIDTH=123 HEIGHT=200 SRC=\"FIGDIR/small/683052v1_fig1.gif\" ALT=\"Figure 1\">\nView larger version (37K):\norg.highwire.dtl.DTLVardef@1acc26corg.highwire.dtl.DTLVardef@1107393org.highwire.dtl.DTLVardef@113eab4org.highwire.dtl.DTLVardef@95f6f4_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOFigure 1.C_FLOATNO Lis1 increases microtubule binding and the velocity of activated dynein complexes. a. Schematic of the current model for dynein activation. Dynein is autoinihibited in the Phi conformation, opens and then adopts a parallel conformation that is seen in the activated dynein complex, which includes dynactin and an activating adaptor. Maximally activated dynein contains two dynein dimers (dynein A and B, far right) b. Schematic of the dynein motor domain with AAA+ ATPase domains colored in rainbow, highlighting the two Lis1 binding sites in yeast dynein, \"sitering\" at AAA3/4 and \"sitestalk\" on dyneins stalk, which leads to dyneins microtubule binding domain (MTBD). Lis1 is shown in orange to the right c. Schematic of the activating adaptor constructs used in this study. d. Binding density (mean {+/-} s.e.m. dynein) of dynein alone on microtubules in the absence (white circles) or presence (black circles) of 300 nM Lis1. Data was normalized to a density of 1.0 in the absence of Lis1. Statistical analysis was performed using a two-tailed unpaired t test; ****, p<0.0001; n = 12 replicates for each condition. e. Binding density (mean {+/-} s.e.m) of dynein/ dynactin/ activating adaptor complexes on microtubules in the absence (white circles) or presence (black circles) of 300 nM Lis1. The activating adaptors used are indicated. Data was normalized to a density of 1.0 in the absence of Lis1. Statistical analysis was performed using a two-tailed unpaired t test; ****, p<0.0001; n = 12 replicates for each condition. f. Velocity of dynein/ dynactin/ activating adaptor complexes in the absence (white circles) or presence (black circles) of 300 nM Lis1. The median and interquartile range are shown and the activating adaptors used are indicated. Statistical analysis was performed using a two-tailed Mann-Whitney test; ****, p<0.0001; ns, p=0.3498; n (individual single molecule events) = 506 (BicD2-S no Lis1), 569 (BicD2-S with Lis1), 496 (BicD2-L no Lis1), 505 (BicD2-L with Lis1), 454 (Hook3 no Lis1), 471 (Hook3 with Lis1), 490 (Ninl no Lis1), 582 (Ninl with Lis1). g. Percent processive runs (mean {+/-} s.e.m.) of dynein/ dynactin/ Hook3 complexes in a higher salt buffer (60 mM KOAc versus 30 mM KOAc in our standard motility buffer) in the absence (white circles) or presence (black circles) of 300 nM Lis1. Statistical analysis was performed using a one-way ANOVA and Tukeys multiple comparisons test; ****, p<0.0001; n = 3 replicates per condition. h. Schematic of the peroxisome relocation assay. i. Peroxisome velocity in human U2OS cells with scrambled or Lis1 siRNA knockdown. The median and interquartile range are shown. Statistical analysis was performed using a two-tailed unpaired t test; ***, p=0.0002; n (average peroxisome velocity per cell) = 30 per condition. More than 7 events were measured per cell.\n\nC_FIG