Hydroxysteroid dehydrogenase family proteins on lipid droplets through bacteria, C. elegans, and mammals.

Lipid droplets (LDs) are the main fat storing sites in almost all species from bacteria to humans. The perilipin family has been found as LD proteins in mammals, Drosophila, and a couple of slime molds, but no bacterial LD proteins containing sequence conservation were identified. In this study, we reported that the hydroxysteroid dehydrogenase (HSD) family was found on LDs across all organisms by LD proteomic analysis. Imaging experiments confirmed LD targeting of three representative HSD proteins including ro01416 in RHA1, DHS-3 in C. elegans, and 17ß-HSD11 in human cells. In C. elegans, 17ß-HSD11 family proteins (DHS-3, DHS-4 and DHS-19) were localized on LDs in distinct tissues. In intestinal cells of C. elegans, DHS-3 targeted to cytoplasmic LDs, while DHS-9 labeled nuclear LDs. Furthermore, the N-terminal hydrophobic domains of 17ß-HSD11 family were necessary for their targeting to LDs. Last, 17ß-HSD11 family proteins induced LD aggregation, and deletion of DHS-3 in C. elegans caused lipid decrease. Independent of their presumptive catalytic sites, 17ß-HSD11 family proteins regulated LD dynamics and lipid metabolism through affecting the LD-associated ATGL, which was conserved between C. elegans and humans. Together, these findings for HSDs provide a new insight not only into the mechanistic studies of the dynamics and functions of LDs in multiple organisms, but also into understanding the evolutionary history of the organelle.

Identification of small ORF-encoded peptides in mouse serum.

Identification of the coding elements in the genome is fundamental to interpret the development of living systems and species diversity. Small peptides (length < 100 amino acids) have played an important role in regulating the biological metabolism, but their identification has been limited by their size and abundance. Serum is the most important body fluid and is full of small peptides. In this study, we have established a small ORF-encoded peptides (SEPs) database from mouse GENCODE release. This database provides about half a million putative translated SEPs in mouse. We also extract serum proteins from wild type and ob/ob mice, and collect the low molecular weight proteins for mass spectrometric analysis. More than 50 novel SEPs have been discovered. Several SEPs are further verified by biochemical method with newly raised antibodies. These novel SEPs enhance the knowledge about the complexity of serum and provide new clues for the annotation and functional analysis of genes, especially the noncoding elements in the genome.