Lysosomal Marker Antibody Sampler Kit

Background

Lysosomes are single-membrane bound organelles of eukaryotic cells that are critically involved in the digestion of macromolecules mainly delivered by endocytosis and autophagy (1). Degradation occurs through hydrolytic enzymes requiring a low-pH environment (~4.5–5.0). Lysosome-associated membrane proteins play a critical role in lysosomal function (2). Lysosome-associated membrane protein 1 and 2 (LAMP1 and LAMP2) are two abundant lysosomal membrane proteins involved in regulating lysosomal motility during lysosome-phagosome fusion and cholesterol trafficking (3,4). CD63/LAMP3, a member of the tetraspanin family, is expressed on the surface of late endosomes and lysosomes and is also enriched in secreted exosomes (5). Lysosomal integral membrane protein type 2 (LIMP-2, also known as SCARB2) functions in cholesterol transport from the lysosome to the membrane, an important function as cholesterol contributes to various biophysical properties of cell membranes and may contribute to various diseases (6). Mucolipin-1 (MCOLN1, TRPML1), a member of the transient receptor potential ion channel superfamily, is a lysosomal/late endosome Ca²⁺ efflux channel that is important in autophagy and lysosomal biogenesis (7).

The acidic environment of the lysosome is maintained by H+ ATPase (V-ATPase), a large heteromultimeric proton pump located on the lysosomal transmembrane. Vacuolar ATPase enzymes are large, multimeric protein complexes with component proteins found in either the V1 peripheral domain or the V0 integral domain (8). The cytoplasmic V1 domain contains a hexamer of A and B catalytic subunits and several other protein subunits required for ATPase assembly and ATP hydrolysis. The integral V0 V-ATPase domain exhibits protein translocase activity and is responsible for proton transport across the membrane. The V-ATPase subunits ATP6V0c, ATP6V0d1, ATP6V1A, ATP6V1B2, and ATP6V1D interact with the Ragulator protein complex and are essential for amino acid induced activation of mTORC1 on the surface of lysosomes (9). Additionally, ATP6V1A has been shown to interact with SARS-CoV-2 M protein and facilitate viral infection (10,11).

Cathepsins are the most abundant lysosomal proteases that can be categorized into groups of cysteine, serine, and aspartic proteases (12). Cathepsin B (CTSB), a cysteine protease, has been associated with multiple sclerosis (13), rheumatoid arthritis (14), and pancreatitis (15). Expression can correlate with poor prognosis for a variety of forms of cancer (16). Cathepsin D (CTSD) is a lysosomal aspartyl protease that plays a role in neuronal degradation and malignant transformation, particularly in breast cancer (17,18).

β-glucocerebrosidase (GCase) is a lysosomal enzyme that catalyzes the hydrolysis of glucocerebroside into free ceramide and glucose (19). GBA mutations are the most common genetic risk factor for Parkinson’s disease (20).