Fig. 1.
Production of functional recombinant PGRP-SD in insect cells. (A) Purified PGRP-SD (predicted molecular mass: 20 kDa) was analyzed on a 15% SDS-reducing gel, indicating a single protein species. Protein was detected by Coomassie blue staining. Further identification by N-terminal sequencing (EVPIVT) showed a mature protein with the N-terminal signal peptide cleaved. (B) PGRP-SDΔ3 mutant flies are highly susceptible to S. aureus infection compared with WT adults. Injecting 20 ng of rPGRP-SD before infection, however, rescued lethality, producing a survival pattern comparable to that in WT animals. Survival patterns were plotted using Kaplan–Meier analysis. Statistical comparisons (log-rank test) were as follows: WT vs. SD rescue, P = 0.256; SD rescue vs. PGRP-SDJ3, P < 0.0001; WT vs. PGRP-SDJ3, P < 0.0001.