Heparanase, also known as HPSE, is an enzyme that acts both at the cell-surface and within the extracellular matrix to degrade polymeric heparan sulfate molecules into shorter chain length oligosaccharides. [5] [6]
Heparanase, also known as HPSE, is an enzyme that acts both at the cell-surface and within the extracellular matrix to degrade polymeric heparan sulfate molecules into shorter chain length oligosaccharides. [5] [6]
The protein is originally synthesised in an inactive 65 kDa proheparanase form in the golgi apparatus and transferred to late endosomes/lysosomes for transport to the cell-surface. In the lysosome it is proteolytically processed into its active form. Proteolytic processing results in the production of three products,
The 8 kDa and 50 kDa fragments form a heterodimer and it is this heterodimer that constitutes the active heparanase molecule. [7] The linker protein is so called because prior to its excision it physically links the 8 kDa and 50 kDa proheparanase fragments. Complete excision of the linker peptide appears to be a prerequisite to the complete activation of the heparanase enzyme.
Crystal structures of both proheparanase and mature heparanase are available, showing that the linker peptide forms a large helical domain which blocks heparan sulfate molecules from interacting with heparanase. [8] Removal of the linker reveals an extended cleft on the enzyme surface, which contains the heparanase active site. [9]
Heparanase has endoglycosidase activity and cleaves polymeric heparan sulfate molecules at sites which are internal within the polymeric chain. [10] The enzyme degrades the heparan sulfate scaffold of the basement membrane and extracellular matrix. It is also associated with the inflammatory process, by allowing the extravasation of activated T lymphocytes. [11] In ocular surface physiology this activity functions as an off/on switch for the prosecretory mitogen lacritin. Lacritin binds the cell surface heparan sulfate proteoglycan syndecan-1 only in the presence of active heparanase. Heparanase partially or completely cleaves heparan sulfate to expose a binding site in the N-terminal 50 amino acids of syndecan-1. [12]
The successful penetration of the endothelial cell layer that lines the interior surface of blood vessels is an important process in the formation of blood borne tumour metastases. Heparan sulfate proteoglycans are major constituents of this layer and it has been shown that increased metastatic potential corresponds with increased heparanase activity for a number of cell lines. [13] [14] Due to the contribution of heparanase activity to metastasis and also to angiogenesis, the inhibition of heparanase activity it is considered to be a potential target for anti-cancer therapies. [15] [16]
Heparanase has been shown to promote arterial thrombosis and stent thrombosis in mouse models due to the cleavage of anti-coagulant heparan sulfate proteoglycans. [17]
P-selectin is a protein that in humans is encoded by the SELP gene.
Perlecan (PLC) also known as basement membrane-specific heparan sulfate proteoglycan core protein (HSPG) or heparan sulfate proteoglycan 2 (HSPG2), is a protein that in humans is encoded by the HSPG2 gene.
Heparan sulfate (HS) is a linear polysaccharide found in all animal tissues. It occurs as a proteoglycan in which two or three HS chains are attached in close proximity to cell surface or extracellular matrix proteins. It is in this form that HS binds to a variety of protein ligands, including Wnt, and regulates a wide range of biological activities, including developmental processes, angiogenesis, blood coagulation, abolishing detachment activity by GrB, and tumour metastasis. HS has also been shown to serve as cellular receptor for a number of viruses, including the respiratory syncytial virus. A recent study reports that cellular heparan sulfate has a role in SARS-CoV-2 Infection, particularly when the virus attaches with ACE2.
Lacritin is a 12.3 kDa glycoprotein encoded in humans by the LACRT gene. Lacritin's discovery emerged from a screen for factors that stimulate tear protein secretion. Lacritin is a secreted protein found in tears and saliva. Lacritin also promotes tear secretion, the proliferation and survival of epithelial cells, and corneal wound healing Lacritin is thus a multifunctional prosecretory mitogen with cell survival activity. Natural or bacterial cleavage of lacritin releases a C-terminal fragment that is bactericidal.
Syndecan 1 is a protein which in humans is encoded by the SDC1 gene. The protein is a transmembrane heparan sulfate proteoglycan and is a member of the syndecan proteoglycan family. The syndecan-1 protein functions as an integral membrane protein and participates in cell proliferation, cell migration and cell-matrix interactions via its receptor for extracellular matrix proteins. Syndecan-1 is a sponge for growth factors and chemokines, with binding largely via heparan sulfate chains. The syndecans mediate cell binding, cell signaling, and cytoskeletal organization and syndecan receptors are required for internalization of the HIV-1 tat protein.
Syndecans are single transmembrane domain proteins that are thought to act as coreceptors, especially for G protein-coupled receptors. More specifically, these core proteins carry three to five heparan sulfate and chondroitin sulfate chains, i.e. they are proteoglycans, which allow for interaction with a large variety of ligands including fibroblast growth factors, vascular endothelial growth factor, transforming growth factor-beta, fibronectin and antithrombin-1. Interactions between fibronectin and some syndecans can be modulated by the extracellular matrix protein tenascin C.
Glypicans constitute one of the two major families of heparan sulfate proteoglycans, with the other major family being syndecans. Six glypicans have been identified in mammals, and are referred to as GPC1 through GPC6. In Drosophila two glypicans have been identified, and these are referred to as dally and dally-like. One additional glypican has been identified in C. elegans. Glypicans seem to play a vital role in developmental morphogenesis, and have been suggested as regulators for the Wnt and Hedgehog cell signaling pathways. They have additionally been suggested as regulators for fibroblast growth factor and bone morphogenic protein signaling.
Syndecan-4 is a protein that in humans is encoded by the SDC4 gene. Syndecan-4 is one of the four vertebrate syndecans and has a molecular weight of ~20 kDa. Syndecans are the best-characterized plasma membrane proteoglycans. Their intracellular domain of membrane-spanning core protein interacts with actin cytoskeleton and signaling molecules in the cell cortex. Syndecans are normally found on the cell surface of fibroblasts and epithelial cells. Syndecans interact with fibronectin on the cell surface, cytoskeletal and signaling proteins inside the cell to modulate the function of integrin in cell-matrix adhesion. Also, syndecans bind to FGFs and bring them to the FGF receptor on the same cell. As a co-receptor or regulator, mutated certain proteoglycans could cause severe developmental defects, like disordered distribution or inactivation of signaling molecules.
40S ribosomal protein SA is a ribosomal protein that in humans is encoded by the RPSA gene. It also acts as a cell surface receptor, in particular for laminin, and is involved in several pathogenic processes.
Glypican-3 is a protein that, in humans, is encoded by the GPC3 gene. The GPC3 gene is located on human X chromosome (Xq26) where the most common gene encodes a 70-kDa core protein with 580 amino acids. Three variants have been detected that encode alternatively spliced forms termed Isoforms 1 (NP_001158089), Isoform 3 (NP_001158090) and Isoform 4 (NP_001158091).
Glypican-1 is a protein that in humans is encoded by the GPC1 gene.
60S ribosomal protein L29 is a protein that in humans is encoded by the RPL29 gene.
3-beta-glucuronosyltransferase 1 (B3GAT1) is an enzyme that in humans is encoded by the B3GAT1 gene, whose enzymatic activity creates the CD57 epitope on other cell surface proteins. In immunology, the CD57 antigen is also known as HNK1 or LEU7. It is expressed as a carbohydrate epitope that contains a sulfoglucuronyl residue in several adhesion molecules of the nervous system.
Sulfatase 1, also known as SULF1, is an enzyme which in humans is encoded by the SULF1 gene.
Extracellular sulfatase Sulf-2 is an enzyme that in humans is encoded by the SULF2 gene.
Bifunctional heparan sulfate N-deacetylase/N-sulfotransferase 2 is an enzyme that in humans is encoded by the NDST2 gene.
Heparan sulfate glucosamine 3-O-sulfotransferase 3B1 is an enzyme that in humans is encoded by the HS3ST3B1 gene. Heparan sulfate biosynthetic enzymes are key components in generating myriad distinct heparan sulfate fine structures that carry out multiple biologic activities. The enzyme encoded by this gene is a member of the heparan sulfate biosynthetic enzyme family. It is a type II integral membrane protein and possesses heparan sulfate glucosaminyl 3-O-sulfotransferase activity ( HS3ST3A1). The Sulfotransferase domain of this enzyme is highly similar to the same domain of heparan sulfate D-glucosaminyl 3-O-sulfotransferase 3A1 and these two enzymes sulfate an identical disaccharide. This gene is widely expressed, with the most abundant expression in liver and placenta.
Heparanase-2 is an enzyme that in humans is encoded by the HPSE2 gene.
Heparan sulfate glucosamine 3-O-sulfotransferase 2 is an enzyme that in humans is encoded by the HS3ST2 gene.
Heparanase is an enzyme with systematic name heparan sulfate N-sulfo-D-glucosamine endoglucanase. This enzyme catalyses the following chemical reaction