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Biology LibreTexts

11.3A: Antimicrobial Enzymes and Antimicrobial Peptides

Skills to Develop

  1. State how long it takes for immediate innate immunity to become activated and what it involves.
  2. State the function of the following antimicrobial enzymes and peptides:
    1. lysozyme
    2. phospholipase A2
    3. defensins
    4. cathelicidins
    5. lactotransferrin and transferrin

Examples include:

a. Lysozyme , found in in tears, mucous, saliva, plasma , tissue fluid, etc., breaks down peptidoglycan in bacteria causing osmotic lysis. Specifically, it breaks the bond between the N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM), the two sugars that make up the backbone of peptidoglycan (see Fig. 1).

b. Phospholipase A2 is an enzyme that penetrates the bacterial cell wall and hydrolyzes the phospholipids in the bacterial cytoplasmic membrane.

c. Human defensins ) are short cationic peptides 30-40 amino acids long that are directly toxic by disrupting the cytoplasmic membrane of a variety of microorganisms causing leakage of cellular needs (see Fig. 2). They also activate cells for an inflammatory response. Defensins are produced by leukocytes, epithelial cells, and other cells. They are also found in blood plasma and mucus. Certain defensins also disrupt the envelopes of some viruses.

d. Cathelicidins are proteins produced by skin and mucosal epithelial cells. The two peptides produced upon cleavage of the cathelicidin are directly toxic to a variety of microorganisms. One pepitide also can bind to and neutralize LPS from Gram-negative cell walls to reduce inflammation.

e. Lactic and fatty acids, found in perspiration and sebaceous secretions , inhibit microbes on the skin.

f. Lactoferrin and transferrin , found in body secretions, plasma, and tissue fluid, trap iron for use by human cells while preventing its use by microorganisms.

g. Hydrochloric acid and enzymes found in gastric secretions destroy microbes that are swallowed.

Keep in mind that in Unit 3 under "Virulence Factors that Promote Bacterial Colonization of the Host" we learned several mechanisms that various bacteria use to resist the body's antibacterial peptides. By resisting these immediate innate immune defenses, some bacteria have a better chance of colonizing their host.

Summary

  1. Immediate innate immunity begins 0-4 hours after exposure to an infectious agent and involves the action of soluble preformed antimicrobial molecules that circulate in the blood and are found in extracellular tissue fluids.
  2. Lysozyme, found in in tears, mucous, saliva, plasma, tissue fluid, etc., breaks down peptidoglycan  in bacteria causing osmotic lysis.
  3. Phospholipase A2 is an enzyme that penetrates the bacterial cell wall and hydrolyzes the phospholipids in the bacterial cytoplasmic membrane.
  4. Human defensins are short cationic peptides 30-40 amino acids long that are directly toxic by disrupting the cytoplasmic membrane of a variety of microorganisms causing leakage of cellular needs.
  5. Cathelicidins are proteins produced by skin and mucosal epithelial cells that are directly toxic to a variety of microorganisms.
  6. Lactoferrin and transferrin, found in body secretions, plasma, and tissue fluid, trap iron for use by human cells while preventing its use by microorganisms.

Contributors

  • Dr. Gary Kaiser (COMMUNITY COLLEGE OF BALTIMORE COUNTY, CATONSVILLE CAMPUS)