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Employing whole-genome analysis we have characterized a large family of genes coding for calpain-related proteins in three kinetoplastid parasites. We have defined a total of 18 calpain-like sequences in Trypanosoma brucei, 27 in Leishmania major, and 24 in Trypanosoma cruzi. Sequence characterization revealed a well-conserved protease domain in most proteins, although residues critical for catalytic activity were frequently altered. Many of the proteins contain a novel N-terminal sequence motif unique to kinetoplastids. Furthermore, 24 of the sequences contain N-terminal fatty acid acylation motifs indicating association of these proteins with intracellular membranes. This extended family of proteins also includes a group of sequences that completely lack a protease domain but is specifically related to other kinetoplastid calpain-related proteins by a highly conserved N-terminal domain and by genomic organization. All sequences lack the C-terminal calmodulin-related calcium-binding domain typical of most mammalian calpains. Our analysis emphasizes the highly modular structure of calpains and calpain-like proteins, suggesting that they are involved in diverse cellular functions. The discovery of this surprisingly large family of calpain-like proteins in lower eukaryotes that combines novel and conserved sequence modules contributes to our understanding of the evolution of this abundant protein family.

Original publication

DOI

10.1007/s00239-004-0272-8

Type

Journal article

Journal

J Mol Evol

Publication Date

12/2005

Volume

61

Pages

742 - 757

Keywords

Amino Acid Motifs, Amino Acid Sequence, Animals, Calpain, Databases, Protein, Evolution, Molecular, Leishmania major, Molecular Sequence Data, Phylogeny, Protein Structure, Tertiary, Sequence Alignment, Sequence Homology, Amino Acid, Trypanosoma brucei brucei, Trypanosoma cruzi