TABLE 2.

The physical properties of the extracellular loops of the FhuA protein

Loop	Overall chargea	Charge ratiob	Residues	Loop lengthc	Commentsd
				Å
L1	−1	0/−1	Thr170–Ser172	7.0	Very short loop
L2	+1	+1/0	Ala203–Ser208	17.5	Short loop
L3	0	+4/−4	Tyr243–Asn273	105	Large flexible, random coil loop that folds back into the pore lumen
L4	+1	+3/−2	Cys318–His339	73.5	Large loop that contains three helices, and a β strand. The loop also contains a stabilizing disulfide bridge Cys318–Cys329. L4 along with part of the β strands block the access to the pore lumen
L5	−4	+3/−7	Asp394–Asn419	87.5	Large loop that contains a β strand, which partially occludes the pore lumen
L6	+1	+1/0	Arg463–Gly466	10.5	Very short loop
L7	0	+1/−1	Pro502–Pro515	45.5	Flexible loop that does not appear to enter or block the pore lumen
L8	−2	0/−2	Asp552–Phe559	24.5	Short loop
L9	+1	+2/−1	Asp598–Lys611	45.5	Medium sized flexible loop. The movement of L9 does appear to be restricted due to its positioning between two uneven β strands
L10	0	+1/−1	Gly640–Ser654	49.0	Medium sized flexible loop that has potential to block the pore lumen
L11	−2	+1/−3	Asn682–Arg704	77.0	Large loop that contains an anti-parallel β sheet, which protrudes into the pore lumen

^a The total charge of the loop was calculated at pH 7.4.

^b The total number of positive charges of the loop versus its negative charges and was calculated at pH 7.4.

^c The length of the loop under the stretched out conformation was based upon the total number of residues.

^d Comments concern the cork-free FhuA protein.