期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：37
页码：11541-11546
DOI：10.1073/pnas.1515568112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceA profound question in animal biology concerns the origin of germ cells. In the model organism Drosophila melanogaster, oskar directs the assembly of germ plasm that forms and specifies germ cells, but the precise function of its gene product, the Oskar protein, remains poorly understood. Using X-ray crystallography, we determined the 3D structures of an N-terminal fragment (Osk-N) and a C-terminal domain of Oskar (Osk-C). Surprisingly, we discovered that Osk-C has RNA binding function. It binds the 3'UTR of its own mRNA, as well as that of nanos, another gene important for germ-line development. This discovery should direct future mechanistic studies of Oskar for a better understanding of its function in germ cell development. Oskar (Osk) protein plays critical roles during Drosophila germ cell development, yet its functions in germ-line formation and body patterning remain poorly understood. This situation contrasts sharply with the vast knowledge about the function and mechanism of osk mRNA localization. Osk is predicted to have an N-terminal LOTUS domain (Osk-N), which has been suggested to bind RNA, and a C-terminal hydrolase-like domain (Osk-C) of unknown function. Here, we report the crystal structures of Osk-N and Osk-C. Osk-N shows a homodimer of winged-helix-fold modules, but without detectable RNA-binding activity. Osk-C has a lipase-fold structure but lacks critical catalytic residues at the putative active site. Surprisingly, we found that Osk-C binds the 3'UTRs of osk and nanos mRNA in vitro. Mutational studies identified a region of Osk-C important for mRNA binding. These results suggest possible functions of Osk in the regulation of stability, regulation of translation, and localization of relevant mRNAs through direct interaction with their 3'UTRs, and provide structural insights into a novel protein-RNA interaction motif involving a hydrolase-related domain.
