CD107a LAMP-1(lysosome-associated membrane protein-1)
Molecule TypeAntigen ExpressionMolecular Weight
Min / Max
Non-lineage Restricted Molecule
Type 1 glycoprotein
Platelet
T Cell
Endothelial Cell
Macrophage
Dendritic Cell
Epithelium
Melanoma Cell
Neutrophil
Granulocyte
100 / 100
120 / 120

Expression
CD107a is expressed on activated platelets, endothelial cells, tonsillar epithelium, granulocytes, T cells, macrophages, dendritic cells, the lysosomal membrane glycoproteins, degranulated platelets, PHA-activated T cells, TNFa -activated endothelium and FMLP-activated neutrophils, and melanoma cells.  CD107a is expressed on metastatic tumors.  Approximately 1-2% of the total CD107a is expressed at the cell surface and is released into the blood.


Structure
MOLECULAR FAMILY NAME FOR CD107a: Belongs to the lysosome-associated membrane protein family.

CD107a is a single-chain type-1 389 aa glycoprotein.  It contains a 350 aa extracellular domain which contains 19 N-glycosylation sites and 6 O-glycosylation sites, a 24 aa transmembrane domain and an 11 aa cytoplasmic domain.  It has a 39% aa sequence identity with CD107b.  These 2 molecules are the major sialoglycoproteins on lysosomal membranes.  A smaller proportion of CD107a can be detected on the plasma membrane.  The molecule is heavily glycosylated, containing  N-glycans, some of which are composed of very complex poly-N-acetyllactosamines.  Carbohydrates constitute 60%  of the 100-120 kDa.  The major portion of each molecule is located on the luminal side of lysosomes, anchored by a transmembrane region with a short cytoplasmic tail.  The intra-luminal portion of the molecule is comprised of 2 homologous disulfide-linked loops or domains, separated by a hinge region rich in proline and serine residues, which is O-glycosylated.  Each hinge region bears the O-linked carbohydrate.  Both CD107a and CD107b contain the sequence GYXX in their cytoplasmic tails.  This motif is also present in the cytoplasmic tail of CD63 and lysosomal acid phosphatase (LAP), both of which are transported to lysosomes.

MOLECULAR MASS
Cell Type Unreduced Reduced Comment
Platelets 100-120 kDa

POST-TRANSCRIPTIONAL MODIFICATION: No information.

POST-TRANSLATIONAL MODIFICATION

CD107a provides selectins with carbohydrate ligands.  The mature protein has a carbohydrate content of 60%. There are 18 potential N-linked glycosylation sites, some of which link poly-N-acetyllactosamine. The hinge region contains O-linked glycans.  The carbohydrate is essential for maintaining the stability of this molecule.

Ligands
LIGANDS AND MOLECULES ASSOCIATED WITH CD107a

The carbohydrate born by CD107a is bound by lectins such as the selectins CD62L, E and P and has been identified as ligands for galectins, and a  S-type lectin present in the extracellular matrix, through its recognition of N-acetyllactosamine oligosaccharide chains.  In addition, CD62E binds to the sialyl-Lewis x structures displayed by poly-N-acetyllactosamines on CD107a.

Function
CD107a functions in the protection, maintenance and the adhesion of lysosomes.  It has been suggested that CD107b protects the inner surface of the lysosomal membrane by forming a barrier to soluble lysosomal hydrolases. Enzymatic removal of the carbohydrate does not affect lysosomal integrity but their specific function remains unclear.  They bind macromolecules such as galectin-3 (a ligand for CD107a) and may bring such molecules into lysosomes for degradation.  On the cell surface, the carbohydrate group includes Lewis X and is ligands for lectins such as the selectin family.  The upregulated expression of CD107a on the surface of several tumor cell lines has been associated with their enhanced metastatic potential, where they may increase adhesion to extracellular matrix and endothelium.

BIOCHEMICAL ACTIVITY: No information.

DISEASE RELEVANCE AND FUNCTION OF CD107a IN INTACT ANIMAL

CD107a plays a role in tumor cell metastasis.  Highly metastatic tumor cells express more CD107a molecules on the cell surface than poorly metastatic cells.  CD107a is a potential marker for screening for lysomal storage diseases in neonates, with CD107a levels elevated in the plasma from 72% of neonatal patients.  Knockout mice have normal lysosomal function although in the absense of double knockouts, this may reflect a redundancy in their function.  Knockout mice have shown astrogliosis, perhaps reflecting the absence of CD107b in murine brain.

Comments
MOLECULAR INTERACTIONS -
PROTEINS AND DNA ELEMENTS WHICH REGULATE TRANSCRIPTION OF CD107a: No information.

SUBSTRATES: No information.

ENZYMES WHICH MODIFY CD107a: No information.

ADDITIONAL INSIGHTS

The tyrosine motif at the cytoplasmic end serves as a lysosomal targeting signal.

Database accession numbers
AnimalPIRSWISSPROTEMGBL/GENBANK
 
HumanEntrezgene 3916P11279
MouseA28067P11438J03881
MouseM32015
RatA30200P14562M34959
Antibodies

Revised June 25, 2008


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