neutral endopeptidase

neutral endopeptidase, also known as neprilysin, is a zinc-dependent metalloprotease that is integral to the regulation of numerous bioactive peptides. It is encoded by the MME gene in humans and is widely expressed, with high concentrations found in the kidney, brain, and gastrointestinal tract. By cleaving and inactivating signaling peptides, it plays a crucial role in modulating blood pressure, neurotransmission, and inflammatory responses.

Function

The primary function of neutral endopeptidase is the catalytic degradation of a wide array of neuropeptides and circulating hormones. Key substrates include atrial natriuretic peptide, brain natriuretic peptide, substance P, endothelin-1, angiotensin II, and enkephalins. Through this activity, it terminates the signaling of these peptides at cell surface receptors, thereby influencing cardiovascular homeostasis, nociception, and fluid balance. In the central nervous system, its role in degrading amyloid-beta peptide links it to the pathophysiology of Alzheimer's disease. The enzyme's action is counterbalanced by the renin–angiotensin–aldosterone system and other proteolytic pathways.

Structure

Neutral endopeptidase is a type II integral membrane protein anchored to the plasma membrane via a short N-terminal cytoplasmic domain. Its large extracellular region contains the active site, which features a conserved HEXXH zinc-binding motif characteristic of the M13 family of peptidases. The three-dimensional structure, resolved via X-ray crystallography, reveals a prominent central cavity that accommodates peptide substrates. Key residues for catalysis and substrate specificity include Glu584 and Arg102, which interact with the scissile bond and substrate C-terminus, respectively. Its structure is homologous to other enzymes like endothelin-converting enzyme-1.

Clinical significance

Dysregulation of neutral endopeptidase activity is implicated in several major diseases. Reduced activity in the brain is associated with increased accumulation of amyloid-beta plaques, a hallmark of Alzheimer's disease. In the cardiovascular system, its inhibition forms the basis of a therapeutic strategy in heart failure, as seen with drugs like sacubitril in LCZ696. Conversely, its expression is often downregulated in prostate cancer and other malignancies, where it may act as a tumor suppressor. It also serves as the CD10 antigen, a diagnostic marker for common acute lymphoblastic leukemia and certain B-cell lymphomas.

Inhibitors

Pharmacological inhibitors of neutral endopeptidase are designed to potentiate the effects of its substrate peptides, particularly the natriuretic peptides. The first generation includes thiorphan and candoxatril, which demonstrated vasodilatory and natriuretic effects. The most clinically significant advancement is the development of angiotensin receptor-neprilysin inhibitors, exemplified by LCZ696, which combines valsartan with sacubitril. This combination is a cornerstone in managing chronic heart failure as per guidelines from the American College of Cardiology. Other experimental inhibitors are being investigated for potential use in hypertension and renal disease.

Genetics

The MME gene is located on chromosome 3 at locus 3q25.2 in humans. It spans approximately 85 kilobases and consists of 24 exons. Variations and polymorphisms in this gene have been studied for associations with Alzheimer's disease risk and cardiovascular disease susceptibility. Research involving knockout mice for the Mme gene has provided models for studying hypertension, heart failure, and neurodegeneration. Expression of the gene is regulated by various transcription factors and can be influenced by inflammatory cytokines and steroid hormones in different tissues.

Category:Enzymes Category:Peptidases Category:EC 3.4.24