GLB1

Galactosidase, beta 1, also known as GLB1, is a is_associated_with::protein which in humans is encoded by the GLB1 is_associated_with::gene.

The GLB1 protein is a is_associated_with::beta-galactosidase that cleaves the terminal beta-is_associated_with::galactose from is_associated_with::ganglioside substrates and other glycoconjugates. The GLB1 gene also encodes an is_associated_with::elastin binding protein.

In corn (is_associated_with::Zea mays), Glb1 is a gene coding for the storage protein is_associated_with::globulin.

Clinical significance
GM1-gangliosidosis is a is_associated_with::lysosomal storage disease that can be caused by a deficiency of β-galactosidase (GLB1). Some cases of Morquio syndrome B have been shown to be due to GLP1 mutations that cause patients to have abnormal is_associated_with::elastic fibers.

Elastin receptor
The is_associated_with::RNA transcript of the GLB1 gene is alternatively spliced and produces 2 mRNAs. The 2.5-kilobase transcript encodes the beta-galactosidase enzyme of 677 amino acids. The alternative 2.0-kb mRNA encodes a beta-galactosidase-related protein (S-Gal) that is only 546 amino acids long and that has no enzymatic activity. The S-Gal protein does bind is_associated_with::elastin and fragments of elastin that are generated by is_associated_with::proteolysis.

The S-Gal protein is a is_associated_with::peripheral membrane protein that functions as part of an elastin receptor complex on the surface of cells. The elastin receptor complex includes S-Gal, neuraminidase and is_associated_with::Cathepsin A. When elastin-derived is_associated_with::peptides bind to the S-Gal protein then the associated neuraminidase is_associated_with::enzyme activity is activated and responding cells can have altered is_associated_with::signal transduction involving is_associated_with::extracellular signal-regulated kinases and regulated matrix metallopeptidase production. Elastin-derived peptides are chemotactic for some cell types and can alter is_associated_with::cell cycle progression. The ability of the GLB1-derived elastin binding protein and the elastin receptor complex to influence cell proliferation appears to be indirect and involve removal of is_associated_with::sialic acid from extracellular and cell surface proteins such as is_associated_with::growth factor receptors.

The S-Gal protein functions during the normal assembly of is_associated_with::elastin into extracellular is_associated_with::elastic fibers. Elastin is initially present as newly synthesized is_associated_with::tropoelastin which can be found in association with S-Gal. The enzymatic activity of neuraminidase in the elastin receptor complex is involved in the release of tropoelastin molecules from the S-Gal chaperone. is_associated_with::Cathepsin A is also required for normal elastin biosynthesis.