Table 1. FRET distances compared with distances predicted from X-ray Crystal Structures.

FRET pair	SecA Domain	EFRETa	Distance (Å)b	Distance predicted from Crystal Structure (Å)
				1M6Nc	2IBMd	2IPCe	2FSFf	1NL3g
59IAE-59IAN 59AF568-59AF647	NBF1	0.38 ± 0.09 ∼1	33 ± 10 ≤ 44 (0.5 R0)	20	91	83	93	106
402IAE-402IAN 402AF488-402AF568	NBF1	0.19 ± 0.10 0.31 ± 0.03	43 ± 25 54 ± 14	16	43	38	68	55
59IAE-402IAN	NBF1-NBF1	0.40 ± 0.16	33 ± 15	30	66	61	81	81
340IAE-340IAN 340AF488-340AF568	PPXD	0.12 ± 0.08 0.78 ± 0.08	≥32 (1.4 R0) 45 ± 11	50	50	30	21	69
427IAE-427IAN 427AF488-427AF568 427AF568-427AF647	NBF2	0.10 ±.09 0.19 ± 0.02 0.25 ± 0.02	≥48 (1.4 R0) 65 ± 17 68 ± 17	71	35	19	64	44
458AF488-458AF568	NBF2	0.43 ± 0.05	62 ± 15	63	11	49	27	36
470IAE-470IAN 470AF488-470AF568 470AF568-470AF647	NBF2	0.08 ±0.01 0.24 ± 0.02 0.35 ± 0.03	≥49 (1.4 R0) 72 ± 16 87 ± 22	101	13	62	50	55
506AF488-506AF568 506AF568-506AF647	NBF2	0.30 ±0.03 0.70 ± 0.07	71 ± 16 67 ± 17	63	31	48	24	53
696IAE-696IAN 696AF488-696AF548 696AF568-696AF647	HWD	0.08 ± 0.02 0.23 ± 0.02 0.59 ± 0.06	≥53 (1.4 R0) 76 ± 18 73 ± 18	89	78	25	128	120
734AF568-734AF647	HWD	0.43 ± 0.04	85 ± 21	91	94	51	140	127

^aFRET efficiency (E_FRET) was measured by the quenching of the donor fluorescence intensity as described.

^bThe donor-acceptor distance (R) was calculated as described.

^cCoordinates for the antiparallel dimeric B. subtilis SecA crystal structure (PDB ID: 1M6N) were generously provided by John Hunt.

^dZimmer et al. B. subtilis structure (PDB ID: 2IBM).

^eVassylyev et al. T. thermophilus structure (PDB ID: 2IPC).

^fPapanikolau et al. E. coli structure (PDB ID: 2FSF). This structure lacked resolution in the PPXD, predicted distance measurements were obtained by modeling the PPXD based on the B. subtilis structure. Coordinates generously provided by Anastasios Economou.

^gSharma et al. M. tuberculosis structure (PDB ID: 1NL3).