CAP5.5, a life-cycle-regulated, cytoskeleton-associated protein is a member of a novel family of calpain-related proteins in Trypanosoma brucei

The cell shape of African trypanosomes is determined by the presence of an extensive subpellicular microtubule cytoskeleton. Other possible functions of the cytoskeleton, such as providing a potential framework for signalling proteins transducing information from the intracellular and extracellular environment, have not yet been investigated in trypanosomes. In this study, we have identified a novel cytoskeleton-associated protein in Trypanosoma brucei. CAP5.5 is the first member of a new family of proteins in trypanoso mes, characterised by their similarity to the catalytic region of calpain-t ype proteases. CAP5.5 is only expressed in procyclic, but not in bloodstrea m, trypanosomes. Furthermore, CAP5.5 has been shown to be both myristoylate d and palmitoylated, suggesting a stable interaction with the cell membrane . A bioinformatics analysis of the trypanosome genome revealed a diverse fa mily of calpain-related proteins with primary structures similar to CAP5.5, but of varying length. We suggest a nomenclature for this new family of pr oteins in T. brucei. (C) 2001 Elsevier Science B.V. All rights reserved.