Abstract
Cytoplasmic dynein-1 (dynein) is the motor responsible for most retrograde transport of cargoes along microtubules in eukaryotic cells, including organelles, mRNA and viruses. Cargo selectivity and activation of processive motility depend on a group of so-called “activating adaptors” that link dynein to its general cofactor, dynactin, and cargoes. The mechanism by which these adaptors regulate dynein transport is poorly understood. Here, based on crystal structures, quantitative binding studies, and in vitro motility assays, we show that BICD2, CRACR2a, and HOOK3, representing three subfamilies of unrelated adaptors, interact with the same amphipathic helix of the dynein light intermediate chain-1 (LIC1). While the hydrophobic character of the interaction is conserved, the three adaptor subfamilies use different folds (coiled-coil, EF-hand, HOOK domain) and different surface contacts to bind the LIC1 helix with affinities ranging from 1.5 to 15.0 μM. We propose that a tunable LIC1-adaptor interaction modulates dynein’s motility in a cargo-specific manner.
Highlights
Cytoplasmic dynein-1 is the motor responsible for most retrograde transport of cargoes along microtubules in eukaryotic cells, including organelles, mRNA and viruses
Together with HOOK3, examined by us previously[18], BICD2 and CRACR2a represent the three major subfamilies of light intermediate chain-1 (LIC1)–adaptor interactions studied to date
Crystallographic analysis shows that the LIC1–adaptor interaction has a conserved hydrophobic character, with the amphipathic LIC1 helix displaying a nearly identical conformation and its hydrophobic face embedded in a hydrophobic cleft in the three adaptor subfamilies
Summary
A subfamily of dynein–dynactin adaptors, including BICD1–2 and BICDL1–2, Spindly, TRAK1–2 and HAP1, share a coiled-coil segment known as the CC1-box that has been directly implicated in LIC1 binding for some of these proteins[16,18,19]. A 2.4-Å resolution structure of human BICD21–98 in complex with human LIC1433–458 was determined ab initio using the single-wavelength anomalous dispersion method from crystals of selenomethionine-substituted BICD21–98 (Table 1). At the N-terminus, one of the BICD2 chains is disordered, whereas the other chain contains an additional helix (residues E6–E16) that runs antiparallel to the coiled-coil helices. 95.60 0.0 6PSD aMerged dataset from two crystals. bValues in parentheses correspond to the highest resolution shell. cCalculated with the program Phenix.xtriage44. dAnisotropy data correction with HKL2000 eliminated weak, unreliable reflections, while reducing the completeness of the data used in refinement
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