Cysteine Protease
Aspartic Acid

Catalytic Triad

The first step in the reaction mechanism by which cysteine proteases catalyze the hydrolysis of peptide bonds is deprotonation of a thiol in the enzyme's active site by an adjacent amino acid with a basic side chain, usually a histidine residue.

The next step is nucleophilic attack by the deprotonated cysteine's anionic sulfur on the substrate carbonyl carbon. In this step, a fragment of the substrate is released with an amine terminus, the histidine residue in the protease is restored to its deprotonated form, and a thioester intermediate linking the new carboxy-terminus of the substrate to the cysteine thiol is formed.

Therefore, they are also sometimes referred to as thiol proteases. The thioester bond is subsequently hydrolyzed to generate a carboxylic acid moiety on the remaining substrate fragment, while regenerating the free enzyme.

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https://en.m.wikipedia.org/wiki/Catalytic_triad

https://en.m.wikipedia.org/wiki/Aspartic_acid

https://en.m.wikipedia.org/wiki/Cysteine_protease

https://en.m.wikipedia.org/wiki/Serine

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Lectin
Papain
Mannan
Mannose
Mannitol
Polyol
Sugar Alcohol

Mannan-Binding Lectin (MBL)
Serine Proteases (MASPs)
Cysteine Protease

Lectin Binding
Calcium Binding

Mannans are polysaccharides that are linear polymers of the sugar mannose.

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Mannan-binding-lectin-associated serine proteases, characteristics and disease associations

https://pubmed.ncbi.nlm.nih.gov/16189649/

MASP-2 deficiency has been described as the result of a mutation causing the exchange of aspartic acid with a glycine at position 105, a position in the first domain, CUB1, involved in calcium binding. This mutation abolishes the binding to MBL and ficolins, and deprives MASP-2 of functional activity. The index case suffered from recurrent severe infections and autoimmune reactions.

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https://en.m.wikipedia.org/wiki/Mannans

https://en.m.wikipedia.org/wiki/Lectin_pathway

Studies on the inactivation of soluble and immobilized papain by the ascorbic acid-Cu2+ system: a model to propose the effect of free radicals on membrane-bound enzymes in vivo

https://pubmed.ncbi.nlm.nih.gov/11730489/