ENPEP - glutamyl aminopeptidase |Elisa - Clia - Antibody - Protein

Background

Glutamyl aminopeptidase (ENPEP), also known as aminopeptidase A (APA) or CD249, is a zinc-dependent metallopeptidase involved in the regulation of blood pressure, modulation of immune responses, and amino acid metabolism. ENPEP is encoded by the ENPEP gene and functions primarily by cleaving N-terminal glutamyl and aspartyl residues from peptide substrates. As a member of the M1 family of aminopeptidases, ENPEP is a single-pass membrane protein found predominantly in kidney, intestine, and endothelial tissues. It also exists in various immune cells and is a critical regulator in the renin-angiotensin system (RAS), where it facilitates the conversion of angiotensin II to angiotensin III, thereby influencing blood pressure and fluid balance.

ENPEP’s role in the RAS system is pivotal because of its impact on hypertension, cardiovascular diseases, and kidney functions. Additionally, ENPEP has implications in immune response regulation, making it a potential target in the treatment of inflammatory and autoimmune diseases. Research into ENPEP function and expression patterns is essential to better understand how this enzyme could be modulated for therapeutic benefits in hypertension, metabolic disorders, and immune system-related diseases.

Protein Structure

ENPEP is a zinc metallopeptidase that structurally belongs to the M1 family of aminopeptidases. It has a distinctive protein structure with several key domains:

Extracellular Domain:

• The extracellular region of ENPEP is the largest and is responsible for its enzymatic activity. It contains the active site with a critical HEXXH(X)18E motif, which is characteristic of zinc-binding metalloproteases. This sequence motif coordinates the binding of a zinc ion that is essential for its catalytic function.
• The catalytic site of ENPEP includes residues involved in binding and orienting substrates, allowing the cleavage of N-terminal glutamyl or aspartyl residues. This substrate specificity is governed by the spatial arrangement within the active site, which accommodates glutamyl residues.
• Additionally, the extracellular domain has multiple N-glycosylation sites that enhance its stability and enzymatic efficiency, allowing it to function effectively in the cellular environment.

Transmembrane Domain:

• ENPEP is a single-pass type II transmembrane protein with a hydrophobic transmembrane segment. This region anchors ENPEP into the cell membrane, positioning its extracellular catalytic domain in a way that it can interact with circulating peptides. The transmembrane segment is essential for maintaining the protein’s orientation and stability in the cell membrane, allowing it to engage effectively in enzymatic activity and cellular signaling.

Cytoplasmic Tail:

• The cytoplasmic domain of ENPEP is short and has few structural features, primarily functioning in the anchoring and possible signaling roles. Although limited in signaling capacity, this region may interact with intracellular molecules or cytoskeletal elements to maintain the protein’s stability and localization on the membrane.

This structural composition allows ENPEP to perform its enzymatic functions optimally while anchored in the membrane, making it accessible to peptide substrates in the extracellular environment.

Classification and Subtypes

ENPEP belongs to the M1 aminopeptidase family and is classified as a type II integral membrane protein due to its single-pass transmembrane domain. This family of enzymes is characterized by their ability to cleave amino acids from the N-terminal of peptide chains, with specific substrate preferences. ENPEP specifically targets peptides with N-terminal glutamyl or aspartyl residues.

Currently, there are no known subtypes of ENPEP; however, it is closely related to other aminopeptidases in the M1 family, such as aminopeptidase N (ANPEP) and aminopeptidase B (RNPEP), which have distinct substrate specificities and biological roles. Together, these enzymes regulate peptide signaling and degradation processes that influence physiological functions ranging from blood pressure control to immune modulation.

Function and Biological Significance

The main functions of ENPEP revolve around its role as an aminopeptidase and its involvement in peptide hormone regulation, particularly within the renin-angiotensin system (RAS):

Regulation of Blood Pressure:

• In the RAS pathway, ENPEP plays a crucial role by converting angiotensin II (a potent vasoconstrictor) to angiotensin III. Angiotensin III retains some vasoconstrictive activity but also stimulates the release of aldosterone, a hormone that regulates sodium and water balance. By modulating levels of angiotensin II and III, ENPEP influences blood pressure and fluid homeostasis. This role positions ENPEP as a potential therapeutic target for treating hypertension and cardiovascular diseases.

Immune System Modulation:

• ENPEP is expressed on the surface of certain immune cells, including macrophages and dendritic cells, where it contributes to immune responses. Its expression on these cells suggests a role in antigen processing or the modulation of peptide-mediated signaling pathways, which are critical in immune cell activation and response.

Metabolic Regulation and Protein Degradation:

• As a glutamyl aminopeptidase, ENPEP is involved in the metabolism of peptides and the breakdown of proteins, particularly in tissues like the kidney and intestine. Its enzymatic activity aids in the degradation of bioactive peptides, thus modulating the availability of signaling molecules and contributing to tissue homeostasis.

Potential Roles in the Brain:

• Emerging research indicates that ENPEP may also be involved in central nervous system functions, where it might regulate neuropeptides associated with stress, pain, and behavioral responses. Its role in the brain, while less understood, is thought to influence neuroendocrine regulation and responses to physiological stress.

Clinical Issues

Given its roles in the RAS system and immune modulation, alterations in ENPEP expression or activity are associated with several clinical conditions:

Hypertension and Cardiovascular Diseases:

• Dysregulation of ENPEP activity can lead to imbalances in angiotensin II and angiotensin III levels, contributing to hypertension. Abnormally high levels of angiotensin II, due to reduced ENPEP activity, result in increased blood pressure, vasoconstriction, and elevated risk of cardiovascular diseases. Targeting ENPEP or its regulatory mechanisms offers potential therapeutic avenues in managing blood pressure and associated cardiovascular conditions.

Kidney Disorders:

• ENPEP is highly expressed in renal tissue, where it participates in sodium and fluid balance. Altered ENPEP activity can disrupt kidney function, leading to conditions such as chronic kidney disease or renal hypertension. Modulating ENPEP expression or activity is a potential strategy for treating kidney-related disorders.

Autoimmune and Inflammatory Disorders:

• ENPEP expression on immune cells links it to inflammatory and autoimmune responses. Dysregulation may lead to aberrant immune activation, contributing to conditions like rheumatoid arthritis or systemic lupus erythematosus. Therapeutically modulating ENPEP activity on immune cells may have potential in treating these conditions by altering immune response dynamics.

Potential Role in Cancer:

• Emerging studies have suggested that ENPEP may play a role in tumor microenvironments, particularly in cancers where the RAS system is implicated in tumor growth and metastasis. ENPEP’s influence on peptide signaling and immune response could make it a target for cancer therapies designed to disrupt tumor-supportive microenvironments.

Summary

ENPEP, or glutamyl aminopeptidase, is a zinc-dependent metallopeptidase with essential roles in peptide metabolism, immune regulation, and the renin-angiotensin system (RAS). Structurally, it consists of an extracellular domain containing the catalytic zinc-binding site, a single transmembrane segment, and a small cytoplasmic tail. ENPEP cleaves N-terminal glutamyl residues from peptides, a function crucial to its role in converting angiotensin II to angiotensin III in the RAS pathway, influencing blood pressure regulation and fluid homeostasis.

The biological significance of ENPEP extends beyond blood pressure control to immune modulation and potential metabolic roles in the kidney, intestine, and brain. Clinically, dysregulation of ENPEP is associated with hypertension, cardiovascular and kidney diseases, autoimmune conditions, and possibly cancer, making it a promising therapeutic target. Given its impact on multiple physiological systems, ongoing research seeks to understand ENPEP’s regulatory mechanisms and to develop interventions aimed at modulating its function for therapeutic benefit.