Structural basis of diverse sequence-dependent target recognition by the 8kDa dynein light chain

Dyneins are multi-subunit molecular motors that translocate molecular cargo es along microtubules. Other than acting as an essential component of the d ynein motor complex, the 89-residue subunit of dynein light chain (DLC8) al so regulates a number of other biological events by binding to various prot eins and enzymes. Currently known DLC8 targets include neuronal nitric oxid e synthase; the proapoptotic Bcl-2 family member protein designated Bim; a Drosophila RNA localization protein Swallow, myosin V, neuronal scaffolding protein GKAP, and I kappaB alpha, an inhibitor of the NF kappaB transcript ion factor. The DLC8-binding domains of the various targets are confined wi thin a short, continuous stretch of amino acid residues. However, these dom ains do not share any obvious sequence homology with each other. Here, the three-dimensional structures of DLC8 complexed with two peptides correspond ing to the DLC8-binding domains of neuronal nitric oxide synthase and Bim, respectively, were determined by NMR spectroscopy. Although the two DLC8-bi nding peptides have entirely different amino acid sequences, both peptides bind to the protein with a remarkable similar conformation by engaging the symmetric DLC8 dimer through antiparallel a-sheet augmentation via the beta 2 strand of the protein. Structural comparison indicates that the two targe t peptides use different regions within the conformational flexible peptide -binding channels to achieve binding specificity. We have also redetermined the ape-form solution structure of DLC8 in this work. The structures of th e DLC8/target peptide complexes, together with the dynamic properties of th e protein, provide a molecular basis of DLC8's diverse amino acid sequence- dependent target recognition. (C) 2001 Academic Press.