azurophil granule membrane

Definition

Target type: cellularcomponent

The lipid bilayer surrounding an azurophil granule, a primary lysosomal granule found in neutrophil granulocytes that contains a wide range of hydrolytic enzymes and is released into the extracellular fluid. [GOC:bf, PMID:17152095]

The azurophil granule membrane, also known as the primary granule membrane, is a specialized membrane compartment found within neutrophils, a type of white blood cell crucial for innate immunity. These granules are characterized by their dense, azurophilic staining properties due to the presence of various enzymes and antimicrobial proteins. The membrane itself plays a critical role in the biogenesis, maturation, and eventual release of these granules. It is composed of a phospholipid bilayer, similar to other cellular membranes, but with a distinct protein composition that reflects its specialized functions.

The azurophil granule membrane is enriched in several key proteins, including:

* **Myeloperoxidase (MPO):** A heme-containing enzyme that generates highly reactive oxygen species (ROS), such as hypochlorous acid, which have potent antimicrobial activity.
* **Lysozyme:** A hydrolytic enzyme that breaks down bacterial cell walls, contributing to the bactericidal activity of neutrophils.
* **Defensins:** Small, cationic peptides that disrupt bacterial membranes, leading to their destruction.
* **Neutrophil elastase:** A serine protease that degrades extracellular matrix components, facilitating neutrophil migration and tissue remodeling.
* **Cathepsin G:** Another serine protease involved in the degradation of proteins and the activation of other proteolytic enzymes.
* **Proteinase 3:** A serine protease with antimicrobial activity and potential involvement in inflammatory responses.

These proteins are embedded within the membrane and are often associated with specific lipid domains or microdomains. The membrane also contains various receptors and signaling molecules that facilitate the regulated release of granule contents upon activation.

During neutrophil maturation, azurophil granules undergo a complex process of biogenesis and trafficking. The membrane components are synthesized in the endoplasmic reticulum (ER) and transported to the Golgi apparatus, where they are assembled into nascent granules. These granules then mature and acquire their characteristic content. Upon neutrophil activation, the azurophil granules fuse with the plasma membrane, releasing their contents into the extracellular space. This process, known as degranulation, is a critical step in the neutrophil's antimicrobial response and contributes to the resolution of inflammation.

In summary, the azurophil granule membrane is a highly specialized structure that plays a crucial role in the storage, maturation, and release of antimicrobial proteins. Its distinct protein composition and regulated fusion with the plasma membrane contribute to the neutrophil's ability to effectively combat infection and maintain tissue homeostasis.'
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Proteins (20)

Compounds (91)