Secreted microfilarial endochitinase (EC 3.2.1.14) of the lymphatic filarial nematode Brugia malayi, also known historically as the MF1 antigen. The protein is a glycosyl hydrolase family 18 (GH18) chitinase comprising a catalytic GH18 domain and a C-terminal type-2 chitin-binding (CBM14) module, and it catalyses the random endo-hydrolysis of N-acetyl-beta-D-glucosaminide (1->4)-beta-linkages in chitin and chitodextrins. Expression is restricted to the microfilarial (first-stage larval) stage and coincides developmentally with the onset of infectivity to the mosquito vector. The enzyme is stored in the inner body of the microfilaria and is secreted; it is one of the most abundant proteins in microfilarial excretory-secretory products. Functionally it is implicated in degrading chitin-containing structures during parasite development and transmission, including a role in exsheathment of the microfilaria within the mosquito. As a stage-specific, secretion-associated antigen it is a recognized transmission-blocking vaccine candidate in brugian filariasis.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004553 hydrolase activity, hydrolyzing O-glycosyl compounds | IEA GO_REF:0000002 | MODIFY | Summary: Correct but more general than the specific function. This protein is a GH18 endochitinase; the broad parent O-glycosyl-hydrolase term should be replaced by the specific chitinase activity supported by the catalytic activity (EC 3.2.1.14) and experimental chitinolytic data. Reason: The GH18 catalytic domain and demonstrated chitin-degrading activity indicate chitinase activity (GO:0004568, a child of GO:0004553) is the informative molecular-function term. Proposed replacements: chitinase activity |
| GO:0004568 chitinase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Accurate core molecular function. The protein is a GH18-family chitinase with the EC 3.2.1.14 catalytic activity; recombinant Brugia malayi microfilarial chitinase has demonstrated chitin-degrading activity, and chitinolytic bands comigrate with the MF1 antigen. |
| GO:0005576 extracellular region | IEA GO_REF:0000120 | KEEP AS NON CORE | Summary: Consistent with the biology. The enzyme carries an N-terminal signal peptide, is secreted from the inner body of the microfilaria, and is among the most abundant proteins in microfilarial excretory-secretory products, so localization to the extracellular region is appropriate. Localization is not the core function, so retained as non-core. |
| GO:0005975 carbohydrate metabolic process | IEA GO_REF:0000002 | MODIFY | Summary: Correct but over-general. As a chitinase the protein participates in carbohydrate metabolism, but the specific and informative process is chitin catabolism (GO:0006032), which is independently annotated. The broad parent term adds little. Reason: Chitin catabolic process (GO:0006032) is the specific child term capturing the actual biological role; the generic carbohydrate metabolic process is uninformative for this enzyme. Proposed replacements: chitin catabolic process |
| GO:0006032 chitin catabolic process | IEA GO_REF:0000120 | ACCEPT | Summary: Accurate core biological process. Endochitinase activity on chitin (degradation of chitin-containing structures during microfilarial development, transmission, and exsheathment in the mosquito vector) is well supported and represents the gene's principal biological role. |
| GO:0008061 chitin binding | IEA GO_REF:0000120 | KEEP AS NON CORE | Summary: Supported by domain architecture. The protein contains a C-terminal type-2 chitin-binding (CBM14) domain in addition to the GH18 catalytic domain, and multiple residues are annotated as chitin-binding. Chitin binding is a real molecular activity but is ancillary to the catalytic chitinase function, so it is retained as non-core. |
| GO:0008843 endochitinase activity | IEA GO_REF:0000003 | ACCEPT | Summary: Accurate and the most specific molecular-function term for this protein. The UniProt catalytic activity (random endo-hydrolysis of N-acetyl-beta-D-glucosaminide (1->4)-beta-linkages in chitin and chitodextrins; EC 3.2.1.14) is precisely endochitinase activity. Accepted as the core molecular function. |
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