Table 2.

The Mot/Exb family of H⁺/Na⁺ energizers (motors)

Process:	Flagellar Rotation		Outer Membrane Transport
Energy:	pmf	smf	pmf	pmf
Motor:	MotAB	PomAB	ExbBD ↓	TolQR ↓
Interact with:	FliG (rotor)	FliG (rotor)	TonB ↓	TolA ↓
			Many distinct OM receptors (OMRs) (substrate-specific porins)

Topologies of homologous motors
Protein	#TMSs	Protein	#TMSs
MotA or PomA	4 (N- and C-termini, cytoplasm)	ExbB or TolQ	3 (N-terminus, periplasm, C-terminus, cytoplasm)
MotB or PomB	1	ExbD or TolR	1 (interacts with TonB or TolA)
		TonB or TolA	1 (interacts with OMRs)