TABLE 1.

Comparison of structural features of various β-barrel membrane proteins

Protein	Protein Data Bank code	Lumen occlusions	No. of β strands	Diameter	Functional unit	Refs.
				nm
αHL	7AHL	None	14	1.5	Heptameric	4
OprD	2ODJ	L3, L4, L7	18	0.5	Monomer	67
OpdK	2QTK	L3, L4, L7	18	0.8	Monomer	68
LamB	1MAL	Extracellular loopsa	18	0.6	Trimer	69
OmpA	1BXW	None	8	1.0	Monomer	70
OmpF	2OMF	Extracellular loopsb,c	16	1.2	Trimer	71
OmpG	2F1C	Gating loopd	14	2.0	Monomer	15
FecA	1KMO	Plug (87–223) 136	22	4.5 × 3.5e	Monomer	72
FepA	1FEB	N-terminal plug (1–153) 153	22	4.0 × 3.0e	Monomer	73
BtuB	1NQH	N-terminal plug (6–132) 127	22	4.2 × 3.7e	Monomer	74, 75
PapC	3FIP	Various structuresf,g,h	24	4.6 × 2.8e	Dimer	76
FhuA	1BY5	N-terminal plug (1–160) 160	22	3.9 × 4.6e	Monomer	21

^a Inwardly folded loops (L1, L3, and L6) contribute to the constriction of ∼1/2 through the channel.

^b Loops 1 and 4–8 partially close entrance to the lumen.

^c Loop 3 folds inward and constricts the lumen.

^d Loop 6 is involved in the gating activity of the pore thereby reducing access to the lumen.

^e Elliptical cross-sectional sides were determined using C^α positions.

^f Plug (259–335) 77 residues.

^g β-Hairpin (447–465) 19 residues.

^h α-Helix (230–240) 11 residues.