Figure 2. A small subset of tail residues mediate grip during GFP unfolding.

(A) Fraction intracellular degradation for substrates with tails containing LYV tripeptides in otherwise all-glycine cassettes. Gly₁₂ and GA substrates were included as internal controls. (B) Fraction intracellular degradation for substrates with tails containing one tyrosine (Y) in otherwise all-glycine cassettes. Gly₁₂ and GA substrates were included as internal controls. (C) V_max values from Michaelis-Menten analysis of degradation of purified substrates with single-tyrosine cassettes. (D) Rates of ATP hydrolysis by ClpX^ΔN (0.1 μM hexamer) in the presence of ClpP (0.3 μM 14-mer) in the absence (–) or presence of different substrates (15 μM monomer). (E) ATP cost of degrading substrates with single-tyrosine cassettes. Note that the Y-axis is logarithmic. In all panels, values represent averages (± S.D.) of three biological replicates.

Figure 2—figure supplement 1. Comparison of K_M values for substrates tested in vitro; comparison of fitted values for K_M for substrate degradation.

Values are the average of three biological replicates ± S.D. None of the substrates exhibited a substantial increase in K_M, indicating that differences in degradation rates result from differences in grip rather than in initial substrate recognition.

Figure 2—figure supplement 2. Stimulation of ClpXP ATP hydrolysis by purified substrates.

(A) Rates of ATP hydrolysis by ClpX^ΔN (0.1 μM hexamer) in the presence of ClpP (0.3 μM 14-mer) in the absence (–) or presence of different substrates (15 μM monomer). (B) ATP cost of degrading substrates. In both panels, values represent averages (± S.D.) of three biological replicates.