A proteomics-MM/PBSA dual approach for the analysis of SARS-CoV-2 main protease substrate peptide specificity.

The main protease Mpro of SARS-CoV-2 is a well-studied major drug target. Additionally, it has been linked to this virus' pathogenicity, possibly through off-target effects. It is also an interesting diagnostic target. To obtain more data on possible substrates as well as to assess the enzyme's primary specificity a two-step approach was introduced. First, Terminal Amine Isobaric Labeling of Substrates (TAILS) was employed to identify novel Mpro cleavage sites in a mouse lung proteome library. In a second step, using a structural homology model, the MM/PBSA variant MM/GBSA (Molecular Mechanics Poisson-Boltzmann/Generalized Born Surface Area) free binding energy calculations were carried out to determine relevant interacting amino acids. As a result, 58 unique cleavage sites were detected, including six that displayed glutamine at the P1 position. Furthermore, modeling results indicated that Mpro has a far higher potential promiscuity towards substrates than expected. The combination of proteomics and MM/PBSA modeling analysis can thus be useful for elucidating the specificity of Mpro, and thus open novel perspectives for the development of future peptidomimetic drugs against COVID-19, as well as diagnostic tools.

The rate and role of pseudogenes of the Mycobacterium tuberculosis complex.

Whole-genome sequence analyses have significantly contributed to the understanding of virulence and evolution of the Mycobacterium tuberculosis complex (MTBC), the causative pathogens of tuberculosis. Most MTBC evolutionary studies are focused on single nucleotide polymorphisms and deletions, but rare studies have evaluated gene content, whereas none has comprehensively evaluated pseudogenes. Accordingly, we describe an extensive study focused on quantifying and predicting possible functions of MTBC and Mycobacterium canettii pseudogenes. Using NCBI's PGAP-detected pseudogenes, we analysed 25 837 pseudogenes from 158 MTBC and M. canetii strains and combined transcriptomics and proteomics of M. tuberculosis H37Rv to gain insights about pseudogenes' expression. Our results indicate significant variability concerning rate and conservancy of in silico predicted pseudogenes among different ecotypes and lineages of tuberculous mycobacteria and pseudogenization of important virulence factors and genes of the metabolism and antimicrobial resistance/tolerance. We show that in silico predicted pseudogenes contribute considerably to MTBC genetic diversity at the population level. Moreover, the transcription machinery of M. tuberculosis can fully transcribe most pseudogenes, indicating intact promoters and recent pseudogene evolutionary emergence. Proteomics of M. tuberculosis and close evaluation of mutational lesions driving pseudogenization suggest that few in silico predicted pseudogenes are likely capable of neofunctionalization, nonsense mutation reversal, or phase variation, contradicting the classical definition of pseudogenes. Such findings indicate that genome annotation should be accompanied by proteomics and protein function assays to improve its accuracy. While indels and insertion sequences are the main drivers of the observed mutational lesions in these species, population bottlenecks and genetic drift are likely the evolutionary processes acting on pseudogenes' emergence over time. Our findings unveil a new perspective on MTBC's evolution and genetic diversity.

Community-based network analyses reveal emerging connectivity patterns of protein-protein interactions in murine melanoma secretome.

Protein-protein interaction networks (PPINs) are static representations of protein connections in which topological features such as subgraphs (communities) may contain proteins functionally related, revealing an additional layer of interactome complexity. We created two PPINs from the secretomes of a paired set of murine melanocytes (a normal melanocyte and its transformed phenotype). Community structures, identified by a graph clustering algorithm, resulted in the identification of subgraphs in both networks. Interestingly, the underlying structure of such communities revealed shared and exclusive proteins (core and exclusive nodes, respectively), in addition to proteins that changed their location within each community (rewired nodes). Functional enrichment analysis of core nodes revealed conserved biological functions in both networks whereas exclusive and rewired nodes in the tumoral phenotype network were enriched in cancer-related processes, including TGFß signaling. We found a remarkable shift in the tumoral interactome, resulting in an emerging pattern which was driven by the presence of exclusive nodes and may represent functional network motifs. Our findings suggest that the rearrangement in the tumoral interactome may be correlated with the malignant transformation of melanocytes associated with substrate adhesion impediment. The interactions found in core and new/rewired nodes might potentially be targeted for therapeutic intervention in melanoma treatment. SIGNIFICANCE: Malignant transformation is a result of synergistic action of multiple molecular factors in which genetic alterations as well as protein expression play paramount roles. During oncogenesis, cellular crosstalk through the secretion of soluble mediators modulates the phenotype of transformed cells which ultimately enables them to successfully disrupt important signaling pathways, including those related to cell growth and proliferation. Therefore, in this work we profiled the secretomes of a paired set of normal and transformed phenotypes of a murine melanocyte. After assembling the two interactomes, clusters of functionally related proteins (network communities) were observed as well as emerging patterns of network rewiring which may represent an interactome signature of transformed cells. In summary, the significance of this study relies on the understanding of the repertoire of 'normal' and 'tumoral' secretomes and, more importantly, the set of interacting proteins (the interactome) in both of these conditions, which may reveal key components that might be potentially targeted for therapeutic intervention.