Table 1.

Structural studies of secretins

X-ray crystallography
Protein name	System	Domains	Reference	PDB
ETEC GspD	T2SS	N0-N1-N2	[15]	3EZJ
EPEC EscC	T3SS	N0-N1	[16]	3GR5
Electron microscopy
Protein name	System and sample state	Symmetry and	Reference	EMDBa
K. oxytoca GspDPulD	T2SS secretinb	C12	[48]
K. oxytoca GspDPulD	T2SS secretin		[84]
K. oxytoca GspDPulD	T2SS secretinc	C12, closed	[24]
V. cholerae GspDEpsD	T2SS secretin	C12, closed	[25]	1763
Y. enterocolitica YscC	T3SS secretin	C13	[85]
S. typhimurium InvG	T3SS complexd	C20	[30]	1100, 1224
S. typhimurium InvG	T3SS complexe	C20	[86]	1214, 1215
S. typhimurium InvG	T3SS complex	C15	[32]	1871, 1874, 1875
S. flexneri MxiD	T3SS complex		[87]	1422
S. flexneri MxiD	T3SS complex	C12	[31]	1617
N. meningitidis PilQ	T4PS secretin	C12	[88]
N. meningitidis PilQ	T4PS secretin	C12	[26]
N. meningitidis PilQ	T4PS secretin	C4 (quasi C12)	[27]
N. meningitidis PilQ	T4PS secretin-pilus complex	C4 (quasi C12)	[89]
N. meningitidis PilQ	T4PS complexf	C14	[28]
N. gonnorrhoea PilQ	T4PS complexf	C14	[28]
T. thermophilus PilQ	T4PS secretin		[29]
bacteriophage f1 pIV	phage assembly system secretin	C14 (D14), closed	[34]

^aAvailable deposition numbers are indicated.

^bSecretin–pilotin complex

^cSecretin–pilotin complex and trypsinized complex reconstructions.

^dNeedle and base complexes.

^eT3SS complexes from ΔinvJ and ΔprgJ mutants.

^fComplexes in isolated membranes