FIG 3.

Representative two-dimensional class averages illustrating receptor shapes. Class averages, generated with the ISAC program, show examples of Tar-4Q (a to c) and Tar-4E (d to f) particles with no apparent bends (a and d), a bend at the HAMP hinge (b and e), or a bend at the Gly hinge (c and f). Class averages with bends at the Gly hinge were generated by applying an external mask to the nanodisc and periplasmic regions of each primary image in the data set (see the text). See Fig. S1 in the supplemental material for images of all unmasked and masked two-dimensional class averages. The shaded regions in panels c and f show the regions of the individual particles that were masked prior to determination of class averages, thus allowing detection of bends at the glycine hinge (see the text). Straight dashed reference lines are next to each subvolume to aid the eye in distinguishing straight from bent receptors.