Table 2 Evaluation of SecA Solution Dimers.

Organism	Structure	R _G(Å)	^aSAXSχ	N-term in Interface	^bFRET χ² value	Reference and Comments
B. subtilis	1M6N	38.1	25.5	Yes	1.1	Hunt et al.²⁸
E. coli	1M6N (E. coli model)	39.8	17.6	Yes	1.1	SecA-N68 used to model E. coli protomer structure; 1M6N dimer interface
B. subtilis	2IBM	39.5	44.7	No	6.2	Zimmer et al.⁶⁸
B. subtilis	3JV2	45.4	36.4	No	—	Zimmer and Rapoport, 2009
M. tuberculosis SecA1	1NKT AB dimer	46.3	50.5	No	6.7	Sharma et al.⁶³
M. tuberculosis SecA1	1NKT AC dimer	39.8	31.9	(Yes)^c	—	Sharma et al.⁶³; similar arrangement to 1M6N dimer
T. thermophilus	2IPC	44.7	34.3	Yes	4.7	Vassylyev et al.⁶⁴; parallel dimer
E. coli	2FSF	42.9	16.1	No	6.9	Papanikolau et al.³⁴; PPXD from SecA-N68∆NC added to structure
B. subtilis	3JV2 SAXS-based Model	36.9	10.3	Yes	—	3JV2 protomer conformation (Zimmer and Rapoport)⁴⁸; new dimer structure found using SAXS
E. coli	3JV2 SAXS-based Model	38.0	10.6	Yes	2.8	SecA-N68 and 3JV2 CT domains used to model E. coli protomer structure; SAXS-based dimer interface.

^aThe χ value as reported by the FoXS server^60,66 after fitting the structures to SAXS data for E. coli SecA-N95.
^bFifteen FRET-based distance measurements were used from Auclair et al., as listed in Table 1 of the manuscript²². For each measurement, the χ² value was calculated as the square of the difference between observed and theoretical distance, divided by the squared estimated FRET error. The value reported is the reduced χ², namely the sum of the 15 values divided by 15.
^cThis dimer resembles the antiparallel 1M6N dimer but the N-terminus in the interface includes 17 N-terminal residues from the recombinant expression vector.

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