TABLE 3.

Quenching of fluorescence of Trp mutants of MscL by di(Br₂C_18:0)PC

Mutant	Distance between Trp edge and chain on surface (Å)	Trp-Br separation along bilayer normal (d2)	Trp-Br distance d3	Calculated efficiency of quenching with no chain penetration	Experimental efficiency of quenching
A20W	7.2	2.0	13.3	0.16	0.58
I23W	7.0	2.2	13.1	0.21	0.50
L30W	4.8	2.1	10.9	0.41	0.59
V31W	5.2	2.1	11.3	0.36	0.44
F34W	4.6	2.4	10.7	0.45	0.49
L73W	3.5	4.5	9.6	0.49	0.51*
I77W	3.5	0.4	9.6	0.63	0.57*
Y87W	3.5	1.2	9.6	0.61	0.66*

Distances between Trp residues and a lipid molecule docked on the surface of the protein were calculated as described in the text. Distances d2 and d3 are defined in Fig. 5. The efficiencies of quenching expected if lipid fatty acyl chains cannot penetrate into the protein surface were calculated as described in the text. Residues 20–34 are in M1, and residues 73–87 are in M2.

^*Data from Powl et al. (12).