Cell Surface最新文献

The surface of Gram-positive and Gram-negative bacteria contains long hair-like proteinaceous protrusion known as pili or fimbriae. Historically, pilin proteins were considered to play a major role in the transfer of genetic material during bacterial conjugation. Recent findings however elucidate their importance in virulence, biofilm formation, phage transduction, and motility. Therefore, it is crucial to gain mechanistic insights on the subcellular assembly of pili and the localization patterns of their subunit proteins (major and minor pilins) that aid the macromolecular pilus assembly at the bacterial surface. In this article, we review the current knowledge of pilus assembly mechanisms in a wide range of Gram-positive and Gram-negative bacteria, including subcellular localization patterns of a few pilin subunit proteins and their role in virulence and pathogenesis.

The bacterial cell wall is composed of a thick layer of peptidoglycan and cell wall polymers, which are either embedded in the membrane or linked to the peptidoglycan backbone and referred to as lipoteichoic acid (LTA) and wall teichoic acid (WTA), respectively. Modifications of the peptidoglycan or WTA backbone can alter the susceptibility of the bacterial cell towards cationic antimicrobials and lysozyme. The human pathogen Listeria monocytogenes is intrinsically resistant towards lysozyme, mainly due to deacetylation and O-acetylation of the peptidoglycan backbone via PgdA and OatA. Recent studies identified additional factors, which contribute to the lysozyme resistance of this pathogen. One of these is the predicted ABC transporter, EslABC. An eslB mutant is hyper-sensitive towards lysozyme, likely due to the production of thinner and less O-acetylated peptidoglycan. Using a suppressor screen, we show here that suppression of eslB phenotypes could be achieved by enhancing peptidoglycan biosynthesis, reducing peptidoglycan hydrolysis or alterations in WTA biosynthesis and modification. The lack of EslB also leads to a higher negative surface charge, which likely stimulates the activity of peptidoglycan hydrolases and lysozyme. Based on our results, we hypothesize that the portion of cell surface exposed WTA is increased in the eslB mutant due to the thinner peptidoglycan layer and that latter one could be caused by an impairment in UDP-N-acetylglucosamine (UDP-GlcNAc) production or distribution.

Lectins are carbohydrate-binding proteins and are involved in a multitude of biological functions. Lectins at the surface of plant cells often occur as lectin receptor-like kinases (LecRLK) anchored to the plasma membrane. These LecRLKs are part of the plant’s pattern-recognition receptor (PRR) system enabling the plant to perceive threats and respond adequately. Furthermore, plant lectins also occur as secreted proteins, which are associated with stress signalling and defence. The aim of this short review is to provide a general perspective on plant lectins and their role at the cell surface.

The de-methylesterification of the pectic polysaccharide homogalacturonan (HG) by pectin methylesterases (PMEs) is a critical step in the control of plant cell expansion and morphogenesis. Plants have large gene families encoding PMEs but also PME inhibitors (PMEIs) with differ in their biochemical properties. The Arabidopsis thaliana PECTIN METHYLESTERASE INHIBITOR 3 (PMEI3) gene is frequently used as a tool to manipulate pectin methylesterase activity in studies assessing its role in the control of morphogenesis. One limitation of these studies is that the exact biochemical activity of this protein has not yet been determined. In this manuscript we produced the protein in Pichia pastoris and characterized its activity in vitro. Like other PMEIs, PMEI3 inhibits PME activity at acidic pH in a variety of cell wall extracts and in purified PME preparations, but does not affect the much stronger PME activity at neutral pH. The protein is remarkable heat stable and shows higher activity against PME3 than against PME2, illustrating how different members of the large PMEI family can differ in their specificities towards PME targets. Finally, growing Arabidopsis thaliana seedlings in the presence of purified PMEI3 caused a dose-dependent inhibition of root growth associated with the overall inhibition of HG de-methylesterification of the root surface. This suggests an essential in vivo role for PME activity at acidic pH in HG de-methylesterification and growth control. These results show that purified recombinant PMEI3 is a powerful tool to study the connection between pectin de-methylesterification and cell expansion.

Phytophthora infestans, causal agent of late blight in potato and tomato, remains challenging to control. Unravelling its biomechanics of host invasion, and its response to mechanical and chemical stress, could provide new handles to combat this devastating pathogen. Here we introduce two fluorescent molecular sensors, CWP-BDP and NR12S, that reveal the micromechanical response of the cell wall-plasma membrane continuum in P. infestans during invasive growth and upon chemical treatment. When visualized by live-cell imaging, CWP-BDP reports changes in cell wall (CW) porosity while NR12S reports variations in chemical polarity and lipid order in the plasma membrane (PM). During invasive growth, mechanical interactions between the pathogen and a surface reveal clear and localized changes in the structure of the CW. Moreover, the molecular sensors can reveal the effect of chemical treatment to CW and/or PM, thereby revealing the site-of-action of crop protection agents. This mechano-chemical imaging strategy resolves, non-invasively and with high spatio-temporal resolution, how the CW-PM continuum adapts and responds to abiotic stress, and provides information on the dynamics and location of cellular stress responses for which, to date, no other methods are available.

Mycobacterium abscessus is an increasingly prevalent opportunistic pathogen causing both pulmonary and skin and soft tissue infections. It is of increasing concern for immunocompromised individuals, such as those with cystic fibrosis, due to its highly drug resistant nature and ability to evade the host immune system. Current treatments for M. abscessus pulmonary infections are largely ineffective and treatment outcomes are generally poor, thus we urgently require new treatments to combat these infections. Recently, it has been demonstrated that manuka honey is effective against M. abscessus and can improve the inhibitory effect of amikacin. Here, we explore the potential improvement of both azithromycin and tobramycin with the addition of manuka honey against M. abscessus complex. Improved growth inhibition was observed for azithromycin with manuka honey against all M. abscessus subspecies. Improved bactericidal activity was also observed. Importantly, the macrolide resistant M. abscessus subsp. bolletii showed improved inhibition and bactericidal activity was obtained in response to 0.117 g/mL manuka honey MGO40 with 16 µg/mL azithromycin. No improved activity was observed for tobramycin and manuka honey against any of the M. abscessus isolates tested. This demonstrates the potential for antibiotic enhancement by the addition of manuka honey, furthering the applications of therapeutic manuka honey.

Humoral immunity plays a defensive role against invading microbes. However, it has been largely overlooked with respect to Aspergillus fumigatus, an airborne fungal pathogen. Previously, we have demonstrated that surfactant protein D (SP-D), a major humoral component in human lung-alveoli, recognizes A. fumigatus conidial surface exposed melanin pigment. Through binding to melanin, SP-D opsonizes conidia, facilitates conidial phagocytosis, and induces the expression of protective pro-inflammatory cytokines in the phagocytic cells. In addition to melanin, SP-D also interacts with galactomannan (GM) and galactosaminogalactan (GAG), the cell wall polysaccharides exposed on germinating conidial surfaces. Therefore, we aimed at unravelling the biological significance of SP-D during the germination process. Here, we demonstrate that SP-D exerts direct fungistatic activity by restricting A. fumigatus hyphal growth. Conidial germination in the presence of SP-D significantly increased the exposure of cell wall polysaccharides chitin, α-1,3-glucan and GAG, and decreased β-1,3-glucan exposure on hyphae, but that of GM was unaltered. Hyphae grown in presence of SP-D showed positive immunolabelling for SP-D. Additionally, SP-D treated hyphae induced lower levels of pro-inflammatory cytokine, but increased IL-10 (anti-inflammatory cytokine) and IL-8 (a chemokine) secretion by human peripheral blood mononuclear cells (PBMCs), compared to control hyphae. Moreover, germ tube surface modifications due to SP-D treatment resulted in an increased hyphal susceptibility to voriconazole, an antifungal drug. It appears that SP-D exerts its anti-A. fumigatus functions via a range of mechanisms including hyphal growth-restriction, hyphal surface modification, masking of hyphal surface polysaccharides and thus altering hyphal immunostimulatory properties.

Latent tuberculosis poses a significant threat to global health through the incubation of undiagnosed infections within the community, and through its tolerance to antibiotics. This Special Features article explores the mechanisms by which the dormant Mycobacterium tuberculosis pathogen can store energy in the form of lipid inclusion bodies and triacylglycerols, which may be key in the development of novel therapeutics to treat TB.

Pathogenic fungi hide from their hosts by camouflage, obscuring immunogenic cell wall components such as beta-glucan with innocuous coverings such as mannoproteins and alpha-glucan that are less readily recognised by the host. Attempts to understand how such processes are regulated have met with varying success. Typically studies focus on understanding the transcriptional response of fungi to either their reservoir environment or the host. However, such approaches do not fully address this research question, due to the layers of post-transcriptional and post-translational regulation that occur within a cell. Although in animals the impact of post-transcriptional and post-translational regulation has been well characterised, our knowledge of these processes in the fungal kingdom is more limited. Mutations in RNA-binding proteins, like Ssd1 and Candida albicans Slr1, affect cell wall composition and fungal virulence indicating that post-transcriptional regulation plays a key role in these processes. Here, we review the current state of knowledge of fungal post-transcriptional regulation, and link this to potential mechanisms of immune evasion by drawing on studies from model yeast and plant pathogenic fungi. We highlight several RNA-binding proteins that regulate cell wall synthesis and could be involved in local translation of cell wall components. Expanding our knowledge on post-transcriptional regulation in human fungal pathogens is essential to fully comprehend fungal virulence strategies and for the design of novel antifungal therapies.

East Coast Fever is a devastating African cattle disease caused by the apicomplexan parasite, Theileria parva. Little is known about the cell surface, and few proteins have been identified. Here, we take an in silico approach to identify novel cell surface proteins, and predict the structure of four key proteins.