CD107b LAMP-2 (lysosome-associated membrane protein 2)
Molecule TypeAntigen ExpressionMolecular Weight
Min / Max
Non-lineage Restricted Molecule
Type 1 glycoprotein
Platelet
Endothelium
Epithelium
Granulocyte
Melanoma Cell
Tumor Cell
T Cell
Endothelial Cell
Blood Cell
Skeletal muscle
100 / 100
120 / 120

Expression
CD107b is expressed on granulocytes, activated and degranulated platelets, TNFa -activated endothelial cells, tonsillar epithelium and melanoma cells, the lysosomal membrane glycoproteins, TNFa-activated endothelium which is weakly positive and on weak FMLP-activated neutrophils.  CD107b is expressed on metastatic tumors.  Approximately 1-2% of total CD107b is expressed at the cell surface and released into the blood.  CD107b has 2 isoforms, LAMP-2A and LAMP-2B.  LAMP-2A is highly expressed in placenta, lung and liver, less in kidney and pancreas and low in brain and skeletal muscle.  LAMP-2B is highly expressed in sketetal muscle, less in brain, placenta, lung, kidney and pancreas and very low in liver.



Structure
MOLECULAR FAMILY NAME FOR CD107b:  Belongs to the lysosome-associated membrane protein family.

CD107b is a single-pass type-1 382 aa glycoprotein.  It contains a 350 aa  extracellular domain which contains 16 N-glycosylation sites and 10 O-glycosylation sites, a 24 aa transmembrane domain and a 11 aa cytoplasmic domain.  CD107b has a 39% aa sequence identity with CD107a.  These 2 molecules are the major sialoglycoproteins on lysosomal membranes.  A smaller proportion of CD107b 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 total mass.  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 threonine residues, which is O-glycosylated.  The hinge region bears the O-linked carboyhydrate.  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

Alternative splicing  yields 2 different isoforms.

POST-TRANSLATIONAL MODIFICATION

CD107b provides selectins with carbohydrate ligands.  The mature protein has a carbohydrate content of 60%. There are 16 potential N-linked glycosylation sites, some of which link poly-N-acetyllactosamines. The hinge region contains O-linked glycans. The carbohydrate is essential for maintaining the stability of this molecule.

Ligands
LIGANDS AND MOLECULES ASSOCIATED WITH CD107b

The carbohydrates borne by CD107b are bound by lectins such as selectins, CD62L, E and P and has been identified as ligands for galectin and a S-type lectin present in the extracellular matrix through its recognition of N-acetyllactosamine oligosaccharide chains.

Function
CD107b 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.  On the cell surface, the carbohydrate group includes Lewis X and is ligands for lectins such as the selectin family.  The upregulated expression of CD107b 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 CD107b IN INTACT ANIMAL

CD107b plays a role in tumor cell metastasis.  Highly metastatic tumor cell express more CD107b molecules on the cell surface than poorly metastatic cells.  Soluble forms of CD107b are found in circulation and are potential markers for screening for lysomal storage diseases in neonates with levels elevated in the plasma from 72% of neonatal patients.  Knockout mice show vacuolar cardioskeletal myopathy and vacuolation of pancreatic liver and endothelial cells as well as leukocytes.  CD107b deficiency in humans causes Danon disease.

Comments
Alternatively spliced forms of the CD107b gene are expressed in a tissue-specific manner.

MOLECULAR INTERACTIONS -
PROTEINS AND DNA ELEMENTS WHICH REGULATE TRANSCRIPTION OF CD107b
Molecule Comment
SP1 Potential SP1 and AP1 binding sites present in the 5'-flanking region (-172 to -20bp)
AP-1 Potential SP1 and AP-1 binding sites present in the 5'-flanking region (-172 to -20bp)
Kpnl A Kpnl repeat sequence upstream of the promoter sequence might regulate expression

SUBSTRATES: No information.

ENZYMES WHICH MODIFY CD107b: No information.

ADDITIONAL INSIGHTS

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

Database accession numbers
AnimalPIRSWISSPROTEMGBL/GENBANK
 
HumanEntrezgene 3920P13473
MouseA35560P17047J05287
RatA36288P17046D90211
Antibodies

Revised June 25, 2008


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