bims-micpro Biomed News
on Discovery and characterization of microproteins
Issue of 2021‒11‒14
four papers selected by
Thomas Farid Martínez
University of California, Irvine

  1. Front Genet. 2021 ;12 728900
      Transcriptome and ribosome sequencing have revealed the existence of many non-canonical transcripts, mainly containing splice variants, ncRNA, sORFs and altORFs. However, identification and characterization of products that may be translated out of these remains a challenge. Addressing this, we here report on 552 non-canonical proteins and splice variants in the model organism C. elegans using tandem mass spectrometry. Aided by sequencing-based prediction, we generated a custom proteome database tailored to search for non-canonical translation products of C. elegans. Using this database, we mined available mass spectrometric resources of C. elegans, from which 51 novel, non-canonical proteins could be identified. Furthermore, we utilized diverse proteomic and peptidomic strategies to detect 40 novel non-canonical proteins in C. elegans by LC-TIMS-MS/MS, of which 6 were common with our meta-analysis of existing resources. Together, this permits us to provide a resource with detailed annotation of 467 splice variants and 85 novel proteins mapped onto UTRs, non-coding regions and alternative open reading frames of the C. elegans genome.
    Keywords:  C. elegans; LC-MS/MS; MSFragger; PEAKS; altORFs; mass spectrometry; sORFs; timsTOF
  2. Curr Med Chem. 2021 Nov 11.
      Although non-coding RNAs (ncRNAs) were initially thought to be a class of RNA transcripts with no encoding capability, it has been established that some ncRNAs actually contain open reading frames (ORFs), which can be translated into micropeptides or microproteins. Recent studies have reported that ncRNAs-derived micropeptides/microproteins have regulatory functions on various biological and oncological processes. Some of these micropeptides/microproteins act as tumor inhibitors and some as tumor inducers. Understanding the carcinogenic role of ncRNAs-encoded micropeptides/microproteins seems to pose potential challenges to cancer research and offer promising practical perspectives on cancer treatment. In this review, we summarized the present information on the association of ncRNAs-derived micropeptides/microproteins with different types of human cancers. We also mentioned their carcinogenic mechanisms in cancer metabolism, signaling pathways, cell proliferation, angiogenesis, metastasis, and so on. Finally, we discussed the potential clinical value of these micropeptides/microproteins and their potential use in the diagnosis and treatment of cancer. This information may help discover, optimize, and develop new tools based on biological micropeptides/microproteins for the early diagnosis and development of anticancer drugs.
    Keywords:  Cancer; CircRNAs; LncRNAs; MiRNAs; Micropeptides; Microproteins; NcRNAs
  3. J Bacteriol. 2021 Nov 08. JB0035321
      Small proteins of up to ∼50 amino acids are an abundant class of biomolecules across all domains of life. Yet, due to the challenges inherent in their size, they are often missed in genome annotations, and are difficult to identify and characterize using standard experimental approaches. Consequently, we still know few small proteins even in well-studied prokaryotic model organisms. Mass spectrometry (MS) has great potential for the discovery, validation, and functional characterization of small proteins. However, standard MS approaches are poorly suited to the identification of both known and novel small proteins due to limitations at each step of a typical proteomics workflow, i.e., sample preparation, protease digestion, liquid chromatography, MS data acquisition, and data analysis. Here, we outline the major MS-based workflows and bioinformatic pipelines used for small protein discovery and validation. Special emphasis is placed on highlighting the adjustments required to improve detection and data quality for small proteins. We discuss both the unbiased detection of small proteins and the targeted analysis of small proteins of interest. Finally, we provide guidelines to prioritize novel small proteins, and an outlook on methods with particular potential to further improve comprehensive discovery and characterization of small proteins. IMPORTANCE Small proteins of up to ∼50 amino acids play important physiological roles across all domains of life. Mass spectrometry is an ideal approach to detect and characterize small proteins, but many aspects of standard mass spectrometry workflows are biased against small proteins due to their size. Here, we highlight applications of mass spectrometry to study small proteins, emphasizing modifications to standard workflows to optimize the detection of small proteins.
  4. FEBS J. 2021 Nov 07.
      How many different proteins can be produced from a single spliced transcript? Genome annotation projects overlook the coding potential of reading frames other than that of the reference open reading frames (refORFs). Recently, alternative open reading frames (altORFs) and their translational products, alternative proteins (altProts), have been shown to carry out important functions in various organisms. AltORFs overlapping refORFs or other altORFs in a different reading frame may be involved in one fundamental mechanism so far overlooked. A few years ago, it was proposed that altORFs may act as building blocks for chimeric (mosaic) polypeptides, which are produced via multiple ribosomal frameshifting events from a single mature transcript. We adopt terminology from that earlier discussion and call this mechanism mosaic translation. This way of extracting and combining genetic information may significantly increase proteome diversity. Thus, we hypothesize that this mechanism may have contributed to the flexibility and adaptability of organisms to a variety of environmental conditions. Specialized ribosomes acting as sensors probably played a central role in this process. Importantly, mosaic translation may be the main source of protein diversity in genomes that lack alternative splicing. The idea of mosaic translation is a testable hypothesis, although its direct demonstration is challenging. Should mosaic translation occur, we would currently highly underestimate the complexity of translation mechanisms and thus the proteome.
    Keywords:  alternative open reading frame; chimeric protein; mass spectrometry; protein coding potential; ribosomal frameshifting; translation