Table 3.

Comparison of Experimental and Model Structural Parameters for LLhP Chimera and R3: Effects of DNA and Effector Binding

Experimentally derived parameters						Model parameters
Sample	conc. (M×104)	Rc (Å)	Rg (Å)	dmax (Å)	Fita	Rc	Rg	dmax	χ2
LLhP Homodimer
Apo-LLhP	0.24	18.5±0.7	31.1±0.5	90	0.97	18.7b	30.2b	90b	0.76b
LLhP-lacO1	0.70	-	32.7±0.3	100	0.98	-	-	-	-
LLhP-lacO1-HX	0.70	-	33.0±0.2	100	0.98	-	32.7c	100c	0.88c
Lacl Homodimer
Apo-R3	0.32	16.8±0.3	35.8±0.5	110	0.96	16.7d	29.8d	90d	1.8d
						-	34.0e	110e	1.0e
R3-lacO1	0.72	-	34.6±0.3	110	0.96	-	34.1f	110f	1.3f
R3-lacO1-IPTG	0.80	-	35.6±0.2	110	0.97	-g	-	-	-

^aTotal quality estimate defined in GNOM (49), equal to 1.0 for an ideal solution. Model parameters are given for

^bModel of apo-LLhP (see Materials and Methods).

^cModel of DNA-bound LLhP (see Materials and Methods).

^d,e,f Parameters taken from reference (23)

^dis the model of the apo-Lacl dimer taken from the one homodimer of the tetrameric Lacl crystal structure (1lbg chains A and B; (41))

^eis the Lacl R3 dimer model optimized by refinement against the scattering data that shows the extended configuration (as opposed to the folded hinge-helix) for the linker sequence connecting the DBD and regulatory domains

^fis the model for R3-lacO¹ taken without modification from the 1LBG crystal structure (1lbg chains A, B, E, and F). Note that this latter structure is missing 4 base pairs from the DNA sequence (17 basepairs instead of 21) and 11 amino acid residues from the protein, resulting in a somewhat higher than ideal χ² value.

^gNo high-resolution structures are available for the Lacl-lacO¹-IPTG complex.