LC8 dynein light chains (DYNLL) are conserved homodimeric eukaryotic hub proteins that participate in diverse cellular processes. Among the binding partners of DYNLL2, myosin 5a (myo5a) is a motor protein involved in cargo transport. Here we provide a profound characterization of the DYNLL2 binding motif of myo5a in free and DYNLL2-bound form by using nuclear magnetic resonance spectroscopy, X-ray crystallography, and molecular dynamics simulations. In the free form, the DYNLL2 binding region, located in an intrinsically disordered domain of the myo5a tail, has a nascent helical character. The motif becomes structured and folds into a β-strand upon binding to DYNLL2. Despite differences of the myo5a sequence from the consensus binding motif, one peptide is accommodated in each of the parallel DYNLL2 binding grooves, as for all other known partners. Interestingly, while the core motif shows a similar interaction pattern in the binding groove as seen in other complexes, the flanking residues make several additional contacts, thereby lengthening the binding motif. The N-terminal extension folds back and partially blocks the free edge of the β-sheet formed by the binding motif itself. The C-terminal extension contacts the dimer interface and interacts with symmetry-related residues of the second myo5a peptide. The involvement of flanking residues of the core binding site of myo5a could modify the quaternary structure of the full-length myo5a and affect its biological functions. Our results deepen the knowledge of the diverse partner recognition of DYNLL proteins and provide an example of a Janus-faced linear motif.
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