Biology subjects

Liu, S.-Q.

Publications and source records attributed to Liu, S.-Q..

7 recordsLinked to original sources

bioRxiv2022

Preferential cross-linking of the stereospecific complex over the encounter complexes by DOPA2, a faster cross-linker than DSS

Transient protein-protein interactions are fundamental aspects of many biochemical reactions, but they are technically challenging to study. Chemical cross-linking of proteins coupled with mass spectrometry (CXMS) analysis is a powerful tool to facilitate the analysis of transient interactions. Central to this technology are chemical cross-linkers. Here, using two transient heterodimeric complexes--EIN/HPr with a KD of 7 M and EIIAGlc/EIIBGlc with a KD of 25 M--as model systems, we compared the effects of two amine-specific homo-bifunctional cross-linkers of different cross-linking speeds. Protein cross-linking by DOPA2, a di-ortho-phthalaldehyde cross-linker, is 60-120 times faster than that by DSS, an N-hydroxysuccinimide ester cross-linker. We analyzed the differences in the number of cross-links identified that reflected the stereospecific complex (SC), the final lowest-energy conformational state, and that of cross-links that reflected the encounter complexes (ECs), an ensemble of short-lived intermediate conformations mediated by nonspecific electrostatic interactions. We found that the faster DOPA2 cross-linking favored the SC whereas the slower DSS cross-linking favored the ECs. We propose a mechanistic model for this intriguing observation. This study suggests that it is feasible to probe the dynamics of protein-protein interaction using cross-linkers of different cross-linking speeds.

biochemistry↗

bioRxiv2022

Mechanistic origin of different binding affinities of SARS-CoV and SARS-CoV-2 spike RBDs to human ACE2

The receptor-binding domain (RBD) of the SARS-CoV-2 spike protein mediates viral entry into host cells through binding to the cell-surface receptor angiotensin-converting enzyme 2 (ACE2). It has been shown that SARS-CoV-2 RBD (RBDCoV2) has a higher binding affinity to human ACE2 than its highly homologous SARS-CoV RBD (RBDCoV), for which the mechanistic reasons still remain to be elucidated. Here, we used the multiple-replica molecular dynamics (MD) simulations, molecular mechanics Poisson-Boltzmann surface area (MM-PBSA) binding free energy calculations, and interface residue contact network (IRCN) analysis approach to explore the mechanistic origin of different ACE2 binding affinities of these two RBDs. The results demonstrate that, when compared to the RBDCoV2-ACE2 complex, the RBDCoV-ACE2 complex features the enhanced overall structural fluctuations and inter-protein positional movements and increased conformational entropy and diversity. The inter-protein electrostatic attractive interactions are a dominant force in determining the high ACE2 affinities of both RBDs, while the significantly strengthened electrostatic forces of attraction of ACE2 to RBDCoV2 determine the higher ACE2 binding affinity of RBDCoV2 than of RBDCoV. Comprehensive comparative analyses of the residue binding free energy components and IRCNs reveal that, although any RBD residue substitution involved in the charge change can significantly impact the inter-protein electrostatic interaction strength, it is the substitutions at the RBD interface that lead to the overall stronger electrostatic attractive force of RBDCoV2-ACE2, which in turn not only tightens the interface packing and suppresses the dynamics of RBDCoV2-ACE2, but also enhances the ACE2 binding affinity of RBDCoV2 compared to that of RBDCoV. Since the RBD residue substitutions involving gain/loss of the positively/negatively charged residues, in particular those near/at the binding interfaces with the potential to form hydrogen bonds and/or salt bridges with ACE2, can greatly enhance the ACE2 binding affinity, the SARS-CoV-2 variants carrying such mutations should be paid special attention to.

biophysics↗

bioRxiv2021

New exon ignites accelerated evolution of placental gene Nrk in the ancestral lineage of eutherians

Accelerated evolution is often driven by the interaction between environmental factors and genes. However, it remains unclear whether accelerated evolution can be ignited. Here, we focused on adaptive events during the emergence of chorioallantoic placenta. We scanned the chromosome X and identified eight accelerated regions in the ancestral lineage of eutherian mammals. Five of these regions (P = 5.61 x 10-11 ~ 9.03 x 10-8) are located in the five exons of Nik-related kinase (Nrk), which is essential in placenta development and fetoplacental induction of labor. Moreover, a eutherian-specific exogenous exon lack of splice variant was found to be conserved. Structure modelling of NRK suggests that the accelerated exons and the eutherian-specific exon could change the enzymatic activity of eutherian NRK. Since the eutherian-specific exon was surrounded by accelerated exons, it indicates that the accelerated evolution of Nrk may be ignited by the emergence of the new exon in the ancestral lineage of eutherian mammals. The new exon might shift the function of Nrk and provide a new fitness landscape for eutherian species to explore. Although multiple exons were accelerated in both of the Nrk catalytic and regulatory domains, positive selection can only be revealed on the regulatory domain if the branch specific nonsynonymous and synonymous rate test was performed by PAML. Thus, it may be important to detect accelerated evolution when studying positive selection on coding regions. Overall, this work suggests that the fundamental process of placental development and fetoplacental induction of labor has been targeted by positive Darwinian selection. Identifying positively selected placental genes provides insights into how eutherian mammals gain benefits from the invasive chorioallantoic placenta to form one of the most successful groups among terrestrial vertebrates.

evolutionary biology↗

bioRxiv2020

A Fast Lysine Cross-linker DOPA Enables Mass Spectrometry Analyses of Protein Unfolding and Weak Protein-protein Interactions

Chemical cross-linking of proteins coupled with mass spectrometry analysis (CXMS) has become a widely used method for protein structure analysis. Central to this technology are chemical cross-linkers. The most popular cross-linkers are N-hydroxysuccinimide (NHS) esters, which react with protein amino groups relatively slowly over 10 minutes or more while in competition with the hydrolysis reaction of NHS esters. To improve the speed of cross-linking, we developed a new class of amine-selective and non-hydrolyzable di-ortho-phthalaldehyde (DOPA) cross-linkers. DOPA can cross-link proteins in 10 seconds under near physiological conditions, which is 60 times faster than the NHS ester cross-linker DSS. DOPA also works at low pH, low temperature, or in the presence of high concentrations of denaturants such as 8 M urea or 6 M guanidine hydrochloride. Further, DOPA-mediated pulse cross-linking captured the dynamic conformational changes associated with RNase A unfolding. Lastly, DOPA outperformed DSS at capturing weak but specific protein-protein interactions.

biochemistry↗

bioRxiv2020

Novel missense mutation E585K in retinitis pigmentosa leads to compromised RPGR splicing diversity

Mutations in the retinitis pigmentosa GTPase regulator (RPGR) gene, are the major cause of X-linked retinitis pigmentosa (RP). Herein we used whole-exome sequencing to screen possible novel RPGR mutations in RP patients, and identified a novel missense mutation E585K in a patient with early onset but slow disease progression, and a frameshift deletion E998Gfs*78 in a patient with RP sine pigmento and high myopia. Intriguingly, bioinformatic analysis indicated that E585K probably affected RPGR RNA splicing instead of the protein sequence directly. Mini-gene assays in 293T cells revealed that splicing events of the E585K mutant were found to be also exist in wildtype, but with a shifted pattern. In the E585K mini-gene usage of an upstream alternative 5' splice site (5' ss) of exon 14 was enhanced, and other splicing events were suppressed, including the canonical 5' ss of exon 14, skipping of exon 14/15 and retention of intron 14. As a result, RPGR splicing products of the E585K mini-gene were predominated by transcripts containing a 4-bp deletion, with a small fraction of in-frame transcripts containing a retended intron 14, which might explain the slow disease progression in the patient carrying the mutation. RNA-Seq analysis further confirmed existence of these splicing events in endogenous RPGR RNA in human retina, pointing to compromised splicing diversity in the E585K mutant. Our findings thus added to the understanding of genotype-phenotype correlation in RP, and suggested that compromised RPGR splicing diversity might play a role in molecular mechanism of the disease.

genetics↗

bioRxiv2020

Characterization of dynamic age-dependent changes and driver microbes in primate gut microbiota during host's development and healthy aging via captive crab-eating macaque model

Recent population studies have significantly advanced our understanding of how age shapes the gut microbiota. However, the actual role of age could be inevitably confounded due to varying environmental factors in human populations. A well-controlled environment is thus necessary to reduce undesirable cofounding effects, and recapitulate age-dependent taxonomic and functional changes in the healthy primate gut microbiota. Herein we performed 16S rRNA gene sequencing, characterized age-associated gut microbial profiles from infant to elderly crab-eating macaques reared in captivity, and systemically revealed lifelong dynamic changes of primate gut microbiota in the model. While the most significantly age-associated gut microbial taxa were mainly found in commensals such as Faecalibacterium, a set of suspicious pathogens such as Helicobacter were exclusively enriched in infants, pointing to their potential role in host development. Importantly, topology analysis indicated that the connectivity of gut microbial network was even more age-dependent than taxonomic diversity, with its tremendous decline probably linked to the hosts healthy aging. NetShift analysis identified Prevotella 9, Rikenellaceae RC9 gut group and Megasphaera as key drivers during gut microbiota maturation and development, actively involved in age-dependent changes in phenotypes and functions of the gut microbial community. The current study demonstrates lifelong age-dependent changes in healthy primate gut microbiota. Our findings indicate potential importance of appropriate exposure to suspicious pathogens in infant development. The age-associated baseline profiles and driver microbes of primate gut microbiota in the current study could provide new insight into its role in the hosts development and healthy aging.

microbiology↗

bioRxiv2018

Network analysis of lymphocyte nucleus staining image

Background: A complex network has been studied and applied in various disciplines. As network analysis and image processing are based on matrices, this research analysed the changes in the chromatin image of lymphocyte nuclei in peripheral blood of humans using a network motif and static features (static parameters), so as to complete image classification with network method.\n\nMethods: Image processing technology was used to establish a chromatin image network of a cell nucleus; Network analysis tool Pajek was used to display the special motif of an isolated structural hole with different symmetric line values; afterwards, the frequency of occurrence of this structural hole in patients with nasopharyngeal carcinoma and AIDS, and healthy people was computed. Then by applying the network static features as variables, the chromatin images of stained lymphocytes from the three groups of people were classified and recognised by using an extreme learning machine (ELM).\n\nResults: The frequency of occurrence of the isolated structural hole with different symmetric line values was adopted to distinguish the structures of the chromatins of peripheral blood lymphocytes in patients with nasopharyngeal carcinoma and AIDS, and healthy people. Similarly, The static features of the chromatin image network of a cell nucleus were applied to classify and recognise the morphological and structural changes in chromatins for peripheral blood lymphocytes in the three groups of people.\n\nConclusion: The surface chemical and physical characteristics, as well as the polymerisation link status of biomacromolecules such as DNA, RNA, and protein in the lymphocyte nucleus change under certain pathological conditions. The change influences the combination of small molecular staining materials and any associated biomacromolecules. Therefore, various macroscopic and microscopic changes were found in the chromatin images of the cell nucleus. The microscopic changes include the variations of the extent of staining of chromatin in the nuclei, coarseness and direction of the texture therein, the size of stained conglomerations, etc. These changes contribute to the differences in chromatin image networks among the same type of cells across the three groups. Based on this, the model can be used to classify and reorganise certain diseases. The results prove that using complex network to analyse the chromatin structure of a cell nucleus is of significance.

bioinformatics↗