Intest Res.  2014 Apr;12(2):90-95. 10.5217/ir.2014.12.2.90.

Lipopolysaccharide: Basic Biochemistry, Intracellular Signaling, and Physiological Impacts in the Gut

• Rhee SH

• KMID: 2284892
• DOI: http://doi.org/10.5217/ir.2014.12.2.90

Abstract

Lipopolysaccharide (LPS), a main constituent of Gram-negative bacterial membrane, specifically activates Toll-like receptor 4, leading to the production of pleiotropic cytokines/chemokines which in turn regulate inflammatory and innate and subsequent adaptive immune responses. Given that human gut harbors a large collection of commensal bacteria, LPS released by gut microbes is able to make the great impact on gut homeostasis through the intracellular signaling pathways engaged by host-microbial interaction. Emerging evidence indicates that LPS in the gut has a potency to elicit the pathogenesis of intestinal inflammatory diseases such as inflammatory bowel disease and necrotizing enterocolitis. In this review, we discuss the current understanding of the basic biochemistry of LPS, LPS-induced intracellular signaling, and physiological impacts of LPS in the intestine.

Keyword

Lipopolysaccharides; Toll-like receptors; Inflammatory bowel diseases

MeSH Terms

Bacteria
Biochemistry*
Enterocolitis, Necrotizing
Homeostasis
Humans
Inflammatory Bowel Diseases
Intestines
Lipopolysaccharides
Membranes
Toll-Like Receptor 4
Toll-Like Receptors
Lipopolysaccharides
Toll-Like Receptor 4
Toll-Like Receptors

Figure

• 

  Fig. 1 The Gram-negative bacterial envelope is composed of two bacterial membranes, outer and inner membrane. The outer membrane is enriched with lipopolysaccharide (LPS), which is an identifying feature of Gram-negative bacteria such as Escherichia coli. The lipid portion of the outer layer of the outer membrane is exclusively composed of LPS molecules. A single E. coli cell possesses approximately 2 million LPS molecules.

• 

  Fig. 2 Chemical structure of the lipopolysaccharide (LPS) is presented. LPS consists of a polysaccharide, or long chain of sugar, and lipid A. The polysaccharide varies depending on bacterial species and is composed of O-specific chain (O-antigen) and two-part cores (Outer core and Inner core). Lipid A virtually includes two glucosamine sugars modified by phosphate and a variable number of fatty acids. It also has negatively charged phosphate groups.

• 

  Fig. 3 Different molecular species of lipid A are observed in various pathogenic Gram-negative bacteria.

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