Four KH domains of the C. elegans Bicaudal-C ortholog GLD-3 form a globular structural platform |
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Authors: | Katharina Nakel Sophia A Hartung Fabien Bonneau Christian R Eckmann Elena Conti |
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Institution: | 1.Department of Structural Cell Biology, Max-Planck-Institute of Biochemistry, D-82152 Martinsried, Germany;2.Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA;3.Max-Planck-Institute of Molecular Cell Biology and Genetics, D-01307 Dresden, Germany |
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Abstract: | Caenorhabditis elegans GLD-3 is a five K homology (KH) domain-containing protein involved in the translational control of germline-specific mRNAs during embryogenesis. GLD-3 interacts with the cytoplasmic poly(A)-polymerase GLD-2. The two proteins cooperate to recognize target mRNAs and convert them into a polyadenylated, translationally active state. We report the 2.8-Å-resolution crystal structure of a proteolytically stable fragment encompassing the KH2, KH3, KH4, and KH5 domains of C. elegans GLD-3. The structure reveals that the four tandem KH domains are organized into a globular structural unit. The domains are involved in extensive side-by-side interactions, similar to those observed in previous structures of dimeric KH domains, as well as head-to-toe interactions. Small-angle X-ray scattering reconstructions show that the N-terminal KH domain (KH1) forms a thumb-like protrusion on the KH2–KH5 unit. Although KH domains are putative RNA-binding modules, the KH region of GLD-3 is unable in isolation to cross-link RNA. Instead, the KH1 domain mediates the direct interaction with the poly(A)-polymerase GLD-2, pointing to a function of the KH region as a protein–protein interaction platform. |
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Keywords: | post-translational control germline development RNA-binding protein protein– protein interaction SAXS |
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