Question

Murein lipoprotein is critical for maintaining the integrity of the Gram-negative cell envelope and has potent immunostimulatory effects that are similar to bacterial endotoxin. Which of the following is most likely responsible for the toxicity of murein lipoprotein?A. Carboxylic acid group B. Core oligosaccharide C. Amino terminal triglycerideD. m-diaminopimelic acid E. core 55-amino acid polypeptide

Answer 1

Answer:

Lipid A, present as part of a Lipopolysaccharide complex in the outer membrane of gram negative bacteria cell walls, should be the answer, but it does not appear in the options included.  As option C states “Amino terminal triglyceride”, and triglycerides are lipids, then we could explore this option. However, nothing is said about lipoproteins linked to Lipid A (that acts as an endotoxin) to mention carboxyl- or amino- terminals (options A and C), so I would consider the core oligosaccharide option as more probable (see below*).

Explanation:

Murein and peptidoglycan are names used to refer bacterial cell walls main component.  This complex is mainly composed by disaccharide units composed of alterning N-acetyl-muramic acid (that contains the same structure of N-acetylglucosamine, plus a tetrapeptide) and N-acetyl-glucosamine, which  form the backbone of the wall. These are responsible for the strength and shape of the cell.  In Gram negative bacteria, an outer layer called outer membrane, as it contains an important amount of lipids, linked to other molecules, is also present.  There, Lipid A is associated to a core oligosaccharide, and subsequently to the Antigen O (polysaccharide) forming Liposaccharides, wich stabilize and give strength to gram negative cell walls.  

*Lipid A is the main responsible molecule for toxicity in these cell walls. As in question answer options, is included in B option “Oligosaccharide core”, which is closely linked to Lipid A, it could be the option to choose. Moreover, oligo saccharides are involved in toxicity responses in several microorganisms .

Answer 2

Answer:

The answer is B. Core oligosaccharide

Explanation:

The central oligosaccharide is the one that is in charge of producing the highest toxicity of murein since it is incorporated into lipid A, which produces cellular toxicity in gram-negative cells. The oligosaccharide is made of an endotoxin that is released when immune cells begin to destroy gram-negative bacteria. The oligosaccharide is also responsible for maximum toxicity, recognizing antigens and starting with the reaction.