Figure 1. Phylogenetic analyses of typical calpains in metazoa support a model of lineage-specific loss.

Typical calpain EF hand motifs in DIV are highlighted; C-terminal EF hand motifs are absent in Nematoda and Ciona intestinalis. Other domains associated with calpain proteins include: PBH, PalB homology domain with some domain III homology; T/C2, C2 domain originally identified in TRA-3 [33]; Zn²⁺, zinc finger motif-containing; SolH, small optic lobes (SOL) homology domain; MIT 1, microtubule interacting and transport domain; and UCTH1, ubiquitin carboxyl-terminal hydrolase domain. The number of genes encoding proteins with the indicated modular arrangement of domains is indicated, left; the number of EF hands in DIV predicted by custom profile hidden Markov models are shown, right. Clades abbreviations: M, Metazoa; Pl, Placozoa; Eu, Eumetezoa; C, Cnidaria; B, Bilateria; P, Protostomia; D+Ch, Deuterostomia and Chordata; L, Lophotrochozoa; E, Ecdysozoa; N, Nematoda and A, Arthropoda. The tree is not drawn to scale. Protein accession numbers are available in Materials and Methods.