An M(r) 145,000 low-density lipoprotein (LDL)-binding protein is conserved throughout the Kinetoplastida order

In view of the importance of the low-density lipoprotein (LDL)-receptor in Trypanosoma brucei, we have examined whether other bloodstream trypanosomes of medical and veterinary importance (T.b. rhodesiense, T. equiperdum, T. vivax, T. congolense), but also related parasites developing in mammalian (Leishmania donovani) and non-mammalian hosts (Crithidia luciliae and Phytomonas sp. isolated from Euphorbia), would possess an LDL-receptor of their own. (1) All these parasites specifically accumulate human 125I-LDL with a relatively 2.5-fold higher rate for bloodstream trypanosomes. (2) A mixture of monoclonal antibodies raised against T.b. brucei LDL-receptor inhibit binding of LDL to all species but with different efficiency. (3) A single glycoprotein of similar M(r) (gp145) is isolated by LDL-affinity chromatography from all the above species, as well as from both human serum-resistant and sensitive strain of T.b. rhodesiense, and from the bodonid member of the Kinetoplastida Trypanoplasma borelli. (4) Several control experiments including 35S-metabolic labeling of procyclic T.b. brucei and of C. luciliae followed by LDL-affinity chromatography or immunoprecipitation demonstrate that gp145 is indeed synthesised by the parasites and is not a contaminant of the experimental system. (5) In immunoblots and ELISA, these gp145 cross-react with the polyclonal and monoclonal antibodies raised against the LDL-receptor of T.b. brucei, the highest degree of cross-reactivity being found among the members of the Trypanozoon subgroup. (6) Finally, immunisation of mice with the purified LDL-receptor from one strain of T.b. brucei is not sufficient to confer durable protection against another strain of this parasite.