Mannan-binding lectin

From Wikipedia, the free encyclopedia

Mannose-binding lectin (protein C) 2, soluble (opsonic defect)
PDB rendering based on 1hup.
Available structures: 1hup
Identifiers
Symbol(s)	MBL2; COLEC1; HSMBPC; MBL; MBP; MBP1; MGC116832; MGC116833
External IDs	OMIM: 154545 MGI: 96924 HomoloGene: 88328
Gene ontology Molecular Function: • receptor binding • calcium ion binding • sugar binding • mannose binding Cellular Component: • extracellular space • cytoplasm • membrane Biological Process: • complement activation, lectin pathway • phosphate transport • complement activation, classical pathway • response to oxidative stress
RNA expression pattern
More reference expression data
Orthologs
	Human	Mouse
Entrez	4153	17195
Ensembl	ENSG00000165471	ENSMUSG00000024863
Uniprot	P11226	Q3UEK1
Refseq	NM_000242 (mRNA) NP_000233 (protein)	NM_010776 (mRNA) NP_034906 (protein)
Location	Chr 10: 54.2 - 54.2 Mb	Chr 19: 30.3 - 30.31 Mb
Pubmed search	[1]	[2]

Mannose binding lectin (MBL), also named mannose- or mannan-binding protein (MBP), is an important factor in innate immunity.

Contents 1 Function 2 Structure 3 Activation 4 Complexes 5 Clinical significance 6 External links 7 References 8 Further reading

[edit] Function

MBL belongs to the class of collectins in the C-type lectin superfamily, whose function appears to be pattern recognition in the first line of defense in the pre-immune host.

MBL recognizes carbohydrate patterns, found on the surface of a large number of pathogenic micro-organisms, including bacteria, viruses, protozoa and fungi.

Binding of MBL to a micro-organism results in activation of the lectin pathway of the complement system.

[edit] Structure

MBL has an oligomeric structure (400-700 kDa), built of subunits that contain three identical peptide chains of 32 kDa each.

Although MBL can form several oligomeric forms, there are indications that dimers and trimers are not biologically active and at least a tetramer form is needed for activation of complement.

[edit] Activation

The complement system can be activated through three pathways the classical pathway, the alternative pathway, and the mannose-binding (MB) lectin pathway. The most-recently discovered mannose-binding lectin pathway activates complement through the mannose-binding lectin protein. MBL binds to carbohydrates (specifically Mannose and Fucose residues) found on the surface of many pathogens.

For example, MBL has been show to bind to:

• yeasts such as Candida albicans
• viruses such as HIV and influenza A
• many bacteria including Salmonella and Streptococci
• parasites like Leishmania

[edit] Complexes

MBL in the blood is complexed with (bound to) another protein, a serine protease called MASP-2 (MBL-associated serine protease).

In order to activate the complement system when MBL binds to its target (for example, mannose on the surface of a bacterium), the MASP protein functions to cleave the blood protein C4 into C4a and C4b. The C4b fragments can then bind to the surface of the bacterium, and initiate the formation of a C3 convertase.

The subsequent complement cascade catalyzed by C3 convertase results in creating a membrane attack complex, which causes lysis of the pathogen that MBL bound to.

[edit] Clinical significance

It is produced in the liver as a response to infection, and is part of many other factors termed acute phase proteins.

[edit] External links

• MeSH Mannan-Binding+Lectin

[edit] References

[edit] Further reading

v • d • e Protein: lectins animal Calnexin - Calreticulin - CD22 - CD33 - Galectin - Myelin-associated glycoprotein - N-Acetylglucosamine receptor - Selectin - Sialoadhesin animal, calcium-dependent Aggrecan - Asialoglycoprotein receptor - CD94 - Collectin (Mannan-binding lectin) - Mannose receptor - Versican plant Abrin - Ricin - Mitogens (Concanavalin A, Phytohaemagglutinin, Pokeweed mitogen) - Legume lectin

v • d • e Proteins: complement system (C, L, A) Activators CLA: C3-convertase - C5-convertase - MAC (C6, C7, C8, C9) - L: Mannan-binding lectin - A: Factor P/Properdin Enzymes C: C1Q/C1R/C1S - C4 (C4a) - C2 - CLA: C3 (C3a, C3b/iC3b) - C5 (C5a) - L: MASP1 - MASP2 - A: Complement factor B - Factor D Inhibitors CLA: C1-inhibitor - Decay accelerating factor - Factor I - CL: C4BP - A: Factor H Complement receptors CR1 - CR2 - CR3 - CR4 - CD11b/CD11c/CD18 - Anaphylatoxin (C3a, C5a)