Mannan-binding lectin serine protease 1 also known as mannose-associated serine protease 1 (MASP-1) is an enzyme

Enzyme

Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

 that in humans is encoded by the MASP1 gene

Gene

A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

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MASP-1 is involved in the lectin pathway

Mannan-binding lectin pathway

The Mannan-binding lectin pathway is similar in structure to the classical complement pathway, in that, after activation, it proceeds through the action of C4 and C2 to produce activated complement proteins further down the cascade...

 of the complement system

Complement system

The complement system helps or “complements” the ability of antibodies and phagocytic cells to clear pathogens from an organism. It is part of the immune system called the innate immune system that is not adaptable and does not change over the course of an individual's lifetime...

 and is responsible for cleaving C4

Complement component 4

Complement component 4 is a protein involved in the complement system.It is cleaved into proteins 4a and 4b.* C4a is an anaphylatoxin.* C4b forms part of C3-convertase, in conjunction with 2a:* C4b can bind CR1....

 and C2

Complement component 2

Complement C2 is a protein that in humans is encoded by the C2 gene. The protein encoded by this gene is part of the classical pathway of complement system.-Further reading:...

 to form C4b2a, a C3-convertase

C3-convertase

There are two forms of C3-convertase .* The first is an enzyme composed of the C4b-C2a complex, which forms during the classical or lectin pathways of the complement system. It is formed when C1s cleaves off a small peptide fragment of C2 C2b from a membrane-bound C4b-C2a complex.* The second...

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MASP-1 is a serine protease

Serine protease

Serine proteases are enzymes that cleave peptide bonds in proteins, in which serine serves as the nucleophilic amino acid at the active site.They are found ubiquitously in both eukaryotes and prokaryotes...

 that functions as a component of the lectin

Lectin

Lectins are sugar-binding proteins that are highly specific for their sugar moieties. They play a role in biological recognition phenomena involving cells and proteins. For example, some viruses use lectins to attach themselves to the cells of the host organism during infection...

 pathway of complement activation. The complement pathway plays an essential role in the innate and adaptive immune response. MASP-1 is synthesized as a zymogen

Zymogen

A zymogen is an inactive enzyme precursor. A zymogen requires a biochemical change for it to become an active enzyme. The biochemical change usually occurs in a lysosome where a specific part of the precursor enzyme is cleaved in order to activate it...

 and is activated when it complexes with the pathogen recognition molecules of lectin pathway, the mannose-binding lectin and the ficolins. This protein is not directly involved in complement activation but may play a role as an amplifier of complement activation by cleaving complement C2 or by activating another complement serine protease, MASP-2

MASP2 (protein)

Mannan-binding lectin serine protease 2 also known as mannose-binding protein-associated serine protease 2 is an enzyme that in humans is encoded by the MASP2 gene....

. MASP-1 is also able to cleave fibrinogen and factor XIII and may may be involved in coagulation. A splice variant of this gene which lacks the serine protease domain functions as an inhibitor of the complement pathway.

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