Post-genomic analysis of the D. melanogaster genome shows that there are 4 genes encoding 'Calpains':
- CalpA (FBgn0012051) - protein products are 65/94/96 kDa
- CalpB (FBgn0025866) - protein product is 104 kDa
- CaplC (FBgn0260450) - protein product is 77 kDa
- sol/CalpD (FBgn0003464) - protein products are 44/174/166 kDa
Note that CalpA and CalpB are considered typical Calpains, sol/CalpD is atypical, and the CalpC protein is thought to be catalytically inactive. See the CALPAINS gene group report (FBgg0001407) and Friedrich et al 2004 (FBrf0179911) for more details.
However, as of FB2025_01, there are 4 additional non-CG gene reports in FlyBase referred to as 'Calpains':
- Calp14B (FBgn0020226)
- CalpI (FBgn0025105)
- CalpII (FBgn0025104)
- Canp (FBgn0010013)
'Calpain 14B' (Calp14B) was a locus described in a single reference (a 1995 PhD thesis, FBrf0083559), with the only associated information in FlyBase being that it mapped to 14C1. The only sequenced localized Calpain that maps to the 14B-C region is 'CalpC', mapped to 14B13. So 'Calp14B' and 'CalpC' should be merged.
'Calpain I' (CalpI) and 'Calpain II' (CalpII) were isolated as two distinct enzymatic 'activities' in fly extracts by Pinter and Friedrich 1988 (FBrf0047562) - CalpI was activated by low Ca2+, whereas CalpII was activated by high Ca2+. 'Ca2+-activated neutral protease' (Canp) corresponds to a purified protein of 94 kD, characterized by Pinter, Stierandova and Friedrich 1992 (FBrf0055463). Subsequently, both the Friedrich group and another group identified a Calpain-encoding gene (CalpA), encoding a protein of 90-97 kDa (see Emori and Saigo 1994 (FBrf0076707) and Theopold et al. 1995 (FBrf0079503)).
A subsequent personal communication from Pinter in 1988 (FBrf0103417) reported on the possible correspondence between the CalpI, CalpII, Canp and CalpA 'gene' entries in FlyBase (see Pinter 1998 (FBrf0103417)). The conclusion was that any correspondence is unclear, but that: (i) CalpII & Canp are activated by high Ca2+ concentrations and therefore may represent the same thing; (ii) CalpI is activated by lower Ca2+ concentrations and is therefore not the same as either CalpII or Canp; and (iii) CalpA is not detected in cytosol by an antibody staining, so it is unlikely to be same as CalpI/CalpII/Canp since these were originally isolated from cytosolic fractions.
Then, in 2004, Friedrich and colleagues published a post-genomic review of the D. melanogaster (see FBrf0179911). This review states that there are 4 D. melanogaster Calpain genes (CalpA, CalpB, CaplC and sol/CalpD), referring to them as "cytoplasmic Ca2+-activated proteases". It also mentions to the purification of the 94 kDa Calpain isolated in Pinter et al 1992 (FBrf0055463) and the subsequent identification of the CalpA gene, but doesn't explicitly say that they consider them to be the same thing.
Taken together, it seems likely that the CalpII activity corresponds to the Canp protein (94 kDa), and that this protein is encoded by the CalpA gene, which is the only Calpain with a protein product in the range 90-97 kDa). That suggests that the CalpI activity may be encoded by the CalpB gene, or is associated with a different protein isoform of CalpA. However, the true correspondence remains clear. Thus, in order to consolidate the information and gene reports in FlyBase, the CalpI, CalpII and Canp gene reports have been obsoleted (as of FB2025_02) with appropriate notes included in the CalpA report.