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Aminopeptidase – Function, Types and Clinical Relevance

Aminopeptidases are enzymes that break down proteins by cleaving amino acids from the free N-terminus of a peptide chain. They play a key role in digestion and cellular metabolism.

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Things worth knowing about "Aminopeptidase"

Aminopeptidases are enzymes that break down proteins by cleaving amino acids from the free N-terminus of a peptide chain. They play a key role in digestion and cellular metabolism.

What is an Aminopeptidase?

An aminopeptidase is an enzyme belonging to the group of peptidases (also called proteases) that cleaves amino acids from the free N-terminal end of a peptide or protein. This process is referred to as exopeptidase activity, since cleavage occurs from the outside end of the peptide chain – as opposed to endopeptidases, which cleave within the interior of the chain.

Aminopeptidases are found in virtually all living organisms, including bacteria, fungi, plants, animals, and the human body. They are localized in various tissues and cellular compartments, including the small intestinal mucosa, kidneys, liver, and blood plasma.

Biological Functions

Aminopeptidases perform several important functions in the human body:

Digestion: In the small intestine, aminopeptidases – particularly the membrane-bound aminopeptidase N (also known as CD13) – break down dietary proteins into individual amino acids that can then be absorbed into the bloodstream.
Protein processing: They are involved in the maturation and activation of proteins, hormones, and neuropeptides. For example, N-terminal amino acids are cleaved during the activation of certain precursor hormones.
Immune function: Aminopeptidases participate in the processing of antigenic peptides that are presented to the immune system via MHC molecules.
Blood pressure regulation: Certain aminopeptidases (e.g., aminopeptidase A) are involved in the degradation of angiotensin II, thereby playing a role in the renin-angiotensin system.

Key Representatives of Aminopeptidases

Aminopeptidase N (APN / CD13)

Aminopeptidase N is a zinc-dependent metalloprotease and one of the most extensively studied aminopeptidases. It is expressed on the surface of many cell types, especially epithelial cells of the intestine and kidney. CD13 also serves as a receptor for certain viruses (e.g., some coronaviruses) and is used as a tumor marker in various cancers (e.g., acute myeloid leukemia).

Aminopeptidase A (APA)

Aminopeptidase A preferentially cleaves acidic amino acids (glutamic acid, aspartic acid) from the N-terminus. It is involved in the regulation of the renin-angiotensin system and is being investigated as a potential therapeutic target for the treatment of high blood pressure.

Leucine Aminopeptidase (LAP)

Leucine aminopeptidase is another well-characterized member of this enzyme group. Elevated activity levels in the blood can indicate liver disease, biliary tract disorders, or pregnancy, and are used in clinical diagnostics.

Clinical Relevance

Aminopeptidases are not only physiologically important but also clinically significant in several areas:

Diagnostics: Elevated serum levels of certain aminopeptidases (e.g., LAP) can indicate liver or biliary tract disease.
Oncology: CD13/APN is being investigated as a tumor marker and therapeutic target in leukemias and solid tumors.
Infectious diseases: Some viruses use aminopeptidases as entry receptors into cells, making them potential antiviral targets.
Neurology: Aminopeptidases regulate the lifespan of neuropeptides in the brain and are therefore relevant to the development of drugs targeting pain, addiction, and psychiatric conditions.

References

Stryer L et al. – Biochemistry. 9th Edition. W.H. Freeman and Company, 2019.
Rawlings ND, Barrett AJ, Bhatt DL – Handbook of Proteolytic Enzymes. 3rd Edition. Elsevier Academic Press, 2013.
Mina-Osorio P – The moonlighting enzyme CD13: old and new functions to target. Trends in Molecular Medicine, 2008; 14(8): 361–371. PubMed PMID: 18603474.

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