The predominant calcimedins from Trypanosoma brucei comprise a family of flagellar EF-hand calcium-binding proteins.
The cellular complement of calcimedins was identified in Trypanosoma brucei by Ca(2+)-dependent association with phenyl-Sepharose. Predominant calcimedins with molecular mass of 23-26 kDa and 44 kDa, along with minor calcimedins of 96, 120 and 230 kDa, were obtained. The trypanosome calcimedins were unrelated to vertebrate annexins, based upon antibody cross-reactivity and an inability to associate in a Ca(2+)-dependent way with phospholipid vesicles comprised of phosphatidylserine or phosphatidylethanolamine/phosphatidylcholine (1:1, w/w). Partial sequence analysis demonstrated that 44 kDa calcimedin (Tb-44) contained an EF-hand calcium-binding loop. Five CNBr/tryptic fragments exhibited a total of 93% similarity with Tb-17, a 23 kDa EF-hand protein in T. brucei. The trypanosome calcimedins appeared to comprise a family of proteins, based on sequence similarities and antibody cross-reactivity of affinity-purified anti-Tb44 with the 23-26 kDa cluster. No evidence was found for Tb-44 in the related species T. cruzi, Leishmania taraentolae or Crithidia fasciculata. Antibodies against Tb-44 were localized by immunofluorescence along the flagellum of T. brucei. Immunoblot analysis of flagella-enriched preparations demonstrated that Tb-44 and the 23-26 kDa cluster were present in this structure. We conclude that annexin family members are not among the predominant trypanosome proteins that associate with phenyl-Sepharose in a Ca(2+)-dependent way. Instead, the major trypanosome calcimedins comprise a family of flagellar EF-hand calcium-binding proteins.
Wu
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Y
Department of Biological Sciences, Southern Methodist University, Dallas, TX 75275.
Haghighat
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NG
Ruben
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L
D000595:Amino Acid Sequence; D000818:Animals; D017302:Annexins / Q000737:chemistry; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000737:chemistry* / Q000378:metabolism; D005407:Flagella / Q000737:chemistry; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010743:Phospholipids / Q000378:metabolism; D015800:Protozoan Proteins / Q000737:chemistry* / Q000378:metabolism; D016415:Sequence Alignment; D014346:Trypanosoma brucei brucei / Q000737:chemistry*
D017302:Annexins; D002135:Calcium-Binding Proteins; D010743:Phospholipids; D015800:Protozoan Proteins; D002118:Calcium