Cyclical differentiation of Trypanosoma brucei involves changes in the cellular complement of calmodulin-binding proteins

The present study was undertaken to evaluate changes in the complement of calmodulin-binding proteins which accompany cyclical differentiation in Trypanosoma brucei. An [125I]trypanosome calmodulin overlay procedure was used to detect calmodulin-binding proteins with Mr of 126,000 and 106,000 that were present in homogenates of slender bloodstream froms but were absent in procyclic culture forms. Competition assays with unlabeled bovine brain or trypanosome calmodulins indicated that the developmentally regulated proteins associated with calmodulins from either source. Moreover, [125I]bovine brain calmodulin associated with the same proteins as trypanosome calmodulin. Homogenates of T. evansi exhibited the same pattern of calmodulin-binding activity as T. brucei slender bloodstream forms; however, T. cruzi and Leishmania tarentolae contained distinct patterns of calmodulin-binding activity. Mouse serum contained no detectable binding proteins while mouse brain contained predominantly proteins of Mr 210,000, 60,000, and 49,000 which were associated with the trypanosome calmodulin probe. The developmentally regulated calmodulin-binding proteins from T. brucei were in the 10,000g pellet. We conclude that the cellular complement of calmodulin-binding proteins varies during the trypanosome life cycle.