The reference OMIM entry for this protein is 156225

Laminin, alpha-2; lama2
Laminin 2, heavy chain merosin, included
Laminin 2, included
Laminin m, included; lamm, included

DESCRIPTION

Laminin is a heterotrimeric extracellular matrix protein consisting of 3 chains: alpha-1 (LAMA1; 150320), beta-1 (LAMB1; 150240), and gamma-1, formerly called beta-2 (LAMC1; 150290). Several isoforms of each chain have been identified. Laminin-2 (merosin) is a heterotrimer composed of laminin subunits alpha-2, beta-1, and gamma-1. It is the main laminin found in muscle fibers. The LAMA2 gene encodes the alpha-2 chain of laminin-2.

CLONING

Merosin is a protein specifically found in the basement membranes of striated muscle and Schwann cells. It is also found in the basement membrane of placental trophoblasts. Ehrig et al. (1990) compared merosin with laminin, which is thought to be present in all basement membranes. They found that a cDNA clone derived from a merosin fragment contained a 3.4-kb open reading frame encoding 1,130 amino acids. The deduced amino acid sequence of the merosin polypeptide is similar to that of the C-terminal region of the laminin alpha-1 chain. The sequence identity between merosin and laminin is nearly 40% in this region. Like laminin, merosin is associated with the light chains laminin B1 and laminin B2, and the whole molecule has a cross-like structure similar to that of laminin. The authors estimated that the LAMA2 chain is at least 380 kD. Vuolteenaho et al. (1994) determined the primary structure of the laminin M chain (symbolized LAMM by them) from cDNA clones isolated from human placental libraries. The complete chain contains a 22-residue signal peptide and 3,088 residues of the mature M chain (3110 residues total). The M chain has a domain structure similar to that of the human and mouse A chains. Northern blot analysis of human fetal tissues showed that the M chain was expressed in most tissues, but not in liver, thymus, or bone. In situ hybridization localized the expression of the M chain gene to cells of mesenchymal origin. In contrast, expression of the A chain was observed only in kidney, testis, neuroretina, and some regions of the brain, as determined by Northern analyses. Epithelial and endothelial cells were negative for both M and A chain gene transcripts. Pegoraro et al. (2000) identified a novel alternatively spliced isoform of LAMA2. Direct sequencing showed that the isoform has a 138-bp in-frame deletion from nucleotides 4629 to 4766 of the coding sequence corresponding to about 70% of exon 31. This splicing event removes 46 amino acids in the cysteine-rich domain IIIa, just proximal to the triple coiled-coil region that associates with the beta-1 and gamma-1 chains of laminin. Immunofluorescent studies suggested that this isoform may impair proper laminin chain assembly.

GENE FUNCTION

Arahata et al. (1993) indicated that merosin is the same as laminin M, a striated muscle-specific, basal-lamina-associated protein. They found that the protein was reduced in the muscle fibers in Fukuyama congenital muscular dystrophy (253800), suggesting that it may play a primary role in the pathogenesis of that disorder. The laminin alpha-2 subunit is expressed in Schwann cells. Ng et al. (2000) provided evidence for the involvement of the specific trisaccharide unit of the phenolic glycolipid-1 (PGL1) of Mycobacterium leprae (see 246300) in determining the bacterial predilection to the peripheral nerve. PGL1 binds specifically to the native laminin-2 in the basal lamina of Schwann cell-axon units. This binding is mediated by the LG1, LG4, and LG5 modules pr ... More on the omim web site

Subscribe to this protein entry history

June 30, 2020: Protein entry updated
Automatic update: OMIM entry 156225 was added.

Oct. 19, 2018: Additional information
Initial protein addition to the database. This entry was referenced in Bryk and co-workers. (2017).