Table 4.

Ligand binding by recombinant SBPs determined using fluorescence emission quenching of proteins upon binding of the apo- and ferric form of ligands and molecular weights of SBPs and complexes of proteins with the siderophores determined by ESI-MS.

Protein	Liganda	Expected ligand charge at pH 7	Kd (nM)b	Molecular weight (Da)
				Calculatedc	Measuredd
FeuA (Bc_3738)				37094.6	37093
	BB	[BB]0	59 (11)	37976.6	37976
	FeBB	[FeIII(BB)]3-	19 (1)	38029.6	38029
	Ent	[Ent] 0	36 (3)	37763.6	37763
	FeEnt	[FeIII(Ent)]3-	12 (3)	37816.6	37817
FatB (Bc_5106)				37675.4	37675
	PB	[PB]0	77 (9)	38393.4	NDf
	FePB	[FeIII(PB)]3-	127 (1)	38446.4	38445
	FePBν	[FeIII(PBν)]2-	135 (47)	30401.4	38400
	3,4-DHB	[3,4-DHB]1-	191 (69)	37829.4	ND
	Fe(3,4-DHB)	[FeIII(3,4-DHB)]0	nde	37884.4	37884
	Fe(3,4-DHB)2	[FeIII(3,4-DHB)2]3-	1.2 (0.7)	38037.4	38038
FpuA (Bc_4528)				37166.3	37165
	PB	[PB]0	23 (8)	37885.3	ND
	FePB	[FeIII(PB)]3-	175 (35)	37937.3	37937
	FePBν	[FeIII(PBν)]2-	699 (169)	37891.3	37889
	3,4-DHB	[3,4-DHB]0	nd	37320.3	ND
	Fe(3,4-DHB)	[FeIII(3,4-DHB)]1-	nd	37375.3	37374
YfiY (Bc_0616)				37118.3	37116
	Sch	[Sch]0	495 (33)	37537.3	37535
	FeSch	[FeIII(Sch)]0	34 (3)	37590.3	37589
	FeSchν	[FeIII(Schν)]1+	298 (114)	37545.3	ND
YxeB (Bc_0383)				36093.8	36094
	DFO	[DFO]1+	nd	36654.1	ND
	FeDFO	[FeDFO]1+	18 (4)	36706.8	36707
	Fch	[Fch]0	nd	36781.1	ND
	FeFch	[FeFch]0	30 (1)	36833.8	36833

^abacillibactin (BB), enterobactin (Ent), petrobactin (PB), petrobactin photoproduct (PB^ν), 3,4-dihydroxybenzoic acid (3,4-DHB), schizokinen and its photoproduct (Sch and Sch^ν, respectively), desferrioxamine (DFO), and ferrichrome (Fch)

^bThe dissociation constants (K_d) were determined from fluorescence data and are the mean of at least three independent measurements with SD given in parenthesis,

^cCalculated masses of noncovalent complexes were computed using masses of neutral ligand species,

^dMass measured ± 1 Da,

^end – not determined,

^fND – not detected.