Table 1. Space Group Fitting.

Diffraction patterns obtained as calculated Fourier transforms from seven KRAS-GppNHp untilted 2D crystals of proteins assembled onto PC-cholesterol-PS membranes were indexed, boxed, and unbent as described in the Methods section. Statistics for space group fitting were obtained using the 2dx ALLSPACE program, which compares the phases of diffraction pattern reflections for internal consistency with 2D space groups, and outputs phase residuals for each space group fit. Using this algorithm, a perfect fit gives a phase residual of 0°, while a random fit yields a 90° phase residual. Note that because internal phase residual comparisons are not relevant with the primitive (p1) space group, the phase residual for p1 is on the basis of signal-to-noise ratios of observed amplitudes. Each untilted 2D crystal examined gave p3 as the optimal space group and, as shown, the averaged phase residual for the p3 space group is significantly less than all other space groups.

group	residual		group	residual	group
	residual
p1		17.2± 1.3	c12a	54.5± 9.6	p422
	53.9± 6.1
p2		55.8± 6.7	p222	56.4± 8.4	p4212
	63.2± 3.9
p12b		51.5± 10.4	p2221b	60.6± 5.3	p3
	7.8± 4.0
p12a		54.5± 9.6	p2221a	68.0± 3.1	p312
	38.5± 2.6
p121b		58.8± 4.2	p22121	63.3± 3.9	p321
	37.1± 7.0
p121a		53.7± 7.3	c222	56.4± 8.4	p6
	37.7± 7.1
c12b		51.5± 10.4	p4	46.3± 5.9	p622
	50.0± 6.0	6.0