Alpha defensin

Alpha Defensin

Structure of Alpha Defensin

Alpha defensins are a class of antimicrobial peptides that play a crucial role in the innate immune system. They are small, cationic peptides that are primarily found in neutrophils and Paneth cells of the small intestine. Alpha defensins are known for their ability to disrupt the cell membranes of microorganisms, thereby providing a first line of defense against infection.

Structure

Alpha defensins are characterized by their three-dimensional structure, which includes a triple-stranded beta-sheet and a conserved cysteine motif that forms three disulfide bonds. This structure is essential for their stability and function. The image on the right shows the structure of an alpha defensin, highlighting its compact and stable configuration.

Function

The primary function of alpha defensins is to protect the host from pathogens. They achieve this by:

• Disrupting microbial membranes, leading to cell lysis.
• Modulating the immune response by acting as chemotactic agents for immune cells.
• Neutralizing bacterial toxins.

Alpha defensins are effective against a broad range of pathogens, including bacteria, fungi, and viruses.

Expression and Regulation

Alpha defensins are expressed in specific cell types:

• Neutrophils: These white blood cells contain alpha defensins in their azurophilic granules, which are released upon activation.
• Paneth cells: Located in the crypts of Lieberkühn in the small intestine, these cells secrete alpha defensins into the intestinal lumen, contributing to gut immunity.

The expression of alpha defensins is regulated by various factors, including cytokines and microbial products.

Clinical Significance

Alpha defensins have been implicated in several clinical conditions:

• Infectious diseases: Deficiencies or dysfunctions in alpha defensins can lead to increased susceptibility to infections.
• Inflammatory diseases: Overexpression of alpha defensins has been associated with inflammatory conditions such as Crohn's disease.
• Cancer: Altered levels of alpha defensins have been observed in certain types of cancer, suggesting a potential role in tumorigenesis.

Related Pages

• Beta defensin
• Innate immune system
• Antimicrobial peptide