Biology subjects

Osman, S. H.

Publications and source records attributed to Osman, S. H..

3 recordsLinked to original sources

bioRxiv2023

Enhanced surface accessibility of SARS-CoV-2 Omicron spike protein due to an altered glycosylation profile

SARS-CoV-2 spike (S) proteins undergo extensive glycosylation, aiding proper folding, enhancing stability, and evading host immune surveillance. In this study, we used mass spectrometric analysis to elucidate the N-glycosylation characteristics and disulfide bonding of recombinant spike proteins derived from the SARS-CoV-2 Omicron variant (B.1.1.529) in comparison with the D614G spike variant. Furthermore, we conducted microsecond-long molecular dynamics simulations on spike proteins to resolve how the different N-glycans impact spike conformational sampling in the two variants. Our findings reveal that the Omicron spike protein maintains an overall resemblance to the D614G spike variant in terms of site-specific glycan processing and disulfide bond formation. Nonetheless, alterations in glycans were observed at certain N-glycosylation sites. These changes, in synergy with mutations within the Omicron spike protein, result in increased surface accessibility of the macromolecule, including ectodomain, receptor-binding domain, and N-terminal domain. These insights contribute to our understanding of the interplay between structure and function, thereby advancing effective vaccination and therapeutic strategies. TeaserThrough mass spectrometry and molecular dynamics simulations, SARS-CoV-2 Omicron spike is found to be less covered by glycans when compared to the D614G spike variant.

molecular biology↗

bioRxiv2023

Inclusion of glycopeptides in hydrogen/deuterium exchange mass spectrometry analysis of SARS-CoV-2 spike ectodomain provides increased sequence coverage

Hydrogen/deuterium exchange mass spectrometry (HDX-MS) can provide precise analysis of a proteins conformational dynamics across varied states, such as heat-denatured vs. native protein structures, localizing regions that are specifically affected by such conditional changes. Maximizing protein sequence coverage provides high confidence that regions of interest were located by HDX-MS, but one challenge for complete sequence coverage is N-glycosylation sites. The deuteration of glycopeptides has not always been identified in previous reports of HDX-MS analyses, causing significant sequence coverage gaps in heavily glycosylated proteins and uncertainty in structural dynamics in many regions throughout a glycoprotein. We report HDX-MS analysis of the SARS-CoV-2 spike protein ectodomain in its trimeric pre-fusion form, which has 22 predicted N-glycosylation sites per monomer, with and without heat treatment. We identified glycopeptides and calculated their isotopic mass shifts from deuteration. Inclusion of the deu-terated glycopeptides increased sequence coverage of spike ectodomain from 76% to 84%, demonstrated that glycopeptides had been deuterated, and improved confidence in results localizing structural re-arrangements. Inclusion of deuterated glycopeptides improves the analysis of the conformational dynamics of glycoproteins such as viral surface antigens and cellular receptors. Abstract Figure O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=196 SRC="FIGDIR/small/544985v1_ufig1.gif" ALT="Figure 1"> View larger version (34K): org.highwire.dtl.DTLVardef@1d8e1f6org.highwire.dtl.DTLVardef@1db0774org.highwire.dtl.DTLVardef@c68d1eorg.highwire.dtl.DTLVardef@15aed98_HPS_FORMAT_FIGEXP M_FIG C_FIG

biochemistry↗

bioRxiv2020

The role of LmeA, a mycobacterial periplasmic protein, in stabilizing the mannosyltransferase MptA and its product lipomannan under stress

The mycobacterial cell envelope has a diderm structure, composed of an outer mycomembrane, an arabinogalactan-peptidoglycan cell wall, periplasm and an inner membrane. Lipomannan (LM) and lipoarabinomannan (LAM) are structural and immunomodulatory components of this cell envelope. LM/LAM biosynthesis involves a number of mannosyltransferases and acyltransferases, and MptA is an 1,6-mannosyltransferase involved in the final extension of the mannan backbones. Recently, we reported the periplasmic protein LmeA being involved in the maturation of the mannan backbone in Mycobacterium smegmatis. Here, we examined the role of LmeA under stress conditions. We found that the lmeA transcription was upregulated under two stress conditions: stationary growth phase and nutrient starvation. Under both conditions, LAM was decreased, but LM was relatively stable, suggesting that maintaining the cellular level of LM under stress is important. Surprisingly, the protein levels of MptA were decreased in lmeA deletion mutant ({Delta}lmeA) in both stress conditions. The transcript levels of mptA in {Delta}lmeA were similar to or even higher than those in the wildtype, indicating that the decrease of MptA protein was a post-transcriptional event. Consistent with the decrease in MptA, {Delta}lmeA was unable to maintain the cellular level of LM under stress. Even during active growth, overexpression of LmeA led the cells to produce more LM and become more resistant to several antibiotics. Altogether, our study reveals the roles of LmeA in the homeostasis of the MptA mannosyltransferase particularly under stress conditions, ensuring the stable expression of LM and the maintenance of cell envelope integrity.

microbiology↗