Abstract
Lipopolysaccharide (LPS) is a component of the outer membrane of mainly Gram-negative bacteria and cyanobacteria. The LPS molecules from marine and terrestrial bacteria show structural variations, even among strains within the same species living in the same environment. Cyanobacterial LPS has a unique structure, since it lacks heptose and 3-deoxy-d-manno-octulosonic acid (also known as keto-deoxyoctulosonate (KDO)), which are present in the core region of common Gram-negative LPS. In addition, the cyanobacterial lipid A region lacks phosphates and contains odd-chain hydroxylated fatty acids. While the role of Gram-negative lipid A in the regulation of the innate immune response through Toll-like Receptor (TLR) 4 signaling is well characterized, the role of the structurally different cyanobacterial lipid A in TLR4 signaling is not well understood. The uncontrolled inflammatory response of TLR4 leads to autoimmune diseases such as sepsis, and thus the less virulent marine cyanobacterial LPS molecules can be effective to inhibit TLR4 signaling. This review highlights the structural comparison of LPS molecules from marine cyanobacteria and Gram-negative bacteria. We discuss the potential use of marine cyanobacterial LPS as a TLR4 antagonist, and the effects of cyanobacterial LPS on humans and marine organisms.
Highlights
Among the Gram-negative photosynthetic prokaryotes, cyanobacteria constitute a large group that is diverse in physiology, metabolism, and morphology [1]
Cyanobacteria produce a diverse array of secondary metabolites and some of them are toxic in nature
In the TRIF dependent pathway, TRAM binds to the Toll-IL-1 receptor (TIR) domain of TLR4, which leads to the sequential recruitment of TRIF, TRAF6, and TRAF3 [33]
Summary
Among the Gram-negative photosynthetic prokaryotes, cyanobacteria constitute a large group that is diverse in physiology, metabolism, and morphology [1]. Marine cyanobacteria may have evolved to produce a range of bioactive natural products and secondary metabolites as a defense strategy against herbivory and environmental stress factors present in a marine environment [3]. They show diverse bioactivities against a variety of pathogens and act as tumor- and immunosuppressants [4]. Different methods have been employed to analyze the structure of LPSs, including nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry (MS), gas chromatography, and matrix-assisted laser desorption/ionization (MALDI)-MS [8] These techniques are based on the following major steps: extraction, refinement and fragmentation [8]. Further studies may help to prevent anti-inflammatory diseases through cyanobacterial LPS
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