Table 1.

Alkalinization-Inducing Activity and Binding Activity of Flagellin and Flagellin-Derived Peptides

Protein or Peptide	Amino Acid Sequencea	Biological Activity EC50 (nM)b	Binding Affinity IC50 (nM)c
Flagellin	Intact protein, 33 kD	0.30	120
Tyr-flg22	YQRLSTGSRINSAKDDAAGLQIA	0.03	1
flg22	QRLSTGSRINSAKDDAAGLQIA	0.03	2
flg15	RINSAKDDAAGLQIA	0.06	7
flg15-Δ3	RINSAKDDAAGL	15.00	80
flg15-Δ4	RINSAKDDAAG	Antagonist	400
flg15-Δ7	RINSAKDD	Antagonist	400
flg13	NSAKDDAAGLQIA	75.00	600,000
flg8	DAAGLQIA	Inactive	Inactive
flg15-swap8-9	RINSAKDADAGLQIA	14.00	12,000
flg15A.tum.	RVGDASDNAAYWSIA	Inactive	Inactive
flg15R.mel.	RVGQAADNAAYWSIA	Inactive	Inactive
flg15E.coli	RINSAKDDAAGQAIA	0.20	6
Systemin	AVQSKPPSKRDPPKMQTD	Inactive	Inactive

^aAmino acid sequence of synthetic peptides used. Amino acids underlined indicate differences from the sequence in Pseudomonas aeruginosa.

^bConcentration that induces half-maximal alkalinization response in tomato cells. Some of the values are reproduced from Felix et al. (1999). Inactive, no significant alkalinization response when tested in concentrations up to 10 μM (EC₅₀ >> 10,000 nM).

^cConcentration required to reduce binding of ¹²⁵I-Tyr-flg22 to microsomal membranes by 50% when measured after 20 min of incubation at 4°C. Inactive, no significant competition when tested in concentrations up to 100 μM (IC₅₀ >> 100,000 nM).