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Comprehensive Peptide Analysis of Mouse Brain Striatum Identifies Novel sORF‐Encoded Polypeptides

Bio‐active peptides are involved in the regulation of most physiological processes in the body. Classical bio‐active peptides (CBAPs) are cleaved from a larger precursor protein and stored in secretion vesicles from which they are released in the extracellular space. Recently, another non‐classical type of bio‐active peptides (NCBAPs) has gained interest. These typically are not secreted but instead appear to be translated from short open reading frames (sORF) and released directly into the cytoplasm. In contrast to CBAPs, these peptides are involved in the regulation of intra‐cellular processes such as transcriptional control, calcium handling and DNA repair. However, bio‐chemical evidence for the translation of sORFs remains elusive. Comprehensive analysis of sORF‐encoded polypeptides (SEPs) is hampered by a number of methodological and biological challenges: the low molecular mass (many 4–10 kDa), the low abundance, transient expression and complications in data analysis. We developed a strategy to address a number of these issues. Our strategy is to exclude false positive identifications. In total sample, we identified 926 peptides originated from 37 known (neuro)peptide precursors in mouse striatum. In addition, four SEPs were identified including NoBody, a SEP that was previously discovered in humans and three novel SEPS from 5′ untranslated transcript regions (UTRs).