gp72, the 72 kilodalton glycoprotein, is the membrane acceptor site for C3 on XXXX epimastigotes.

@entity3208 @entity1527 @entity8696 @entity38403 @entity2975 @entity3367 @entity13507
We examined the interaction of complement component C3 with surface molecules on @entity1527 . Five- to six-fold more C3 was bound to epimastigotes (Epi) than to metacyclic trypomastigotes (CMT) of strain M88. Epi and CMT were surface iodinated, then incubated in @entity38403 serum, and detergent lysates were applied to anti-C3 antibody that had been coupled to @entity3367 . We found that 9.20-10.24% of applied 125I-Epi protein bound to anti-C3- @entity3367 , compared to 2.64% binding of 125I-CMT protein. @entity3208 - @entity2975 gel electrophoresis showed that C3 was attached to 125I-Epi protein by a covalent bond. Samples eluted from anti-C3- @entity3367 with @entity8696 revealed a single, major, 72 kD band, suggesting that C3b attaches almost exclusively to the 72 kD glycoprotein of Epi by a @entity8696 -susceptible @entity13507 bond. An antiserum was prepared from lysates of serum-treated Epi that had been affinity-purified on anti-C3- @entity3367 . This antiserum immunoprecipitated a single 72 kD component (gp72) from surface-iodinated Epi, and specifically recognized only gp72 from Epi in immunoblots. In contrast to the results with Epi, gp72 on CMT was not found to be an efficient acceptor molecule for C3 deposition. The results are the first to evaluate the acceptor site for C3 deposition on a parasite, and they show that gp72 on Epi, but not gp72 on CMT, serves as the preferential acceptor for C3 during antibody-independent alternative complement pathway activation.
