Table 2. Position and distribution of Trp residues in structures of known transmembrane barrels.

					Position of Trp residued
S. No.a,b	PDB IDc	Proteina,b	# of β-strandsd,e	# of Trp residues	Membrane interface	Transmembrane	Extra-membrane
1	1P4T	NspA	10 (8)	0	-	-	-
2	2POR	Porin	22 (16)	1	1	-	-
3	3QRA	Ail	9 (8)	2	1	1	-
4	1QJ8	OmpX	8 (8)	2	1	1	-
5	2LHF	OprH	10 (8)	2	2	-	-
6	3HW9	OmpF	25 (16)	2	1	1	-
7	1E54	Omp32	24 (16)	2	-	1	1
8	3DZM	TtoA	14 (8)	3	1	-	2
9	3FID	LpxR	17 (12)	3	-	1	2
10	2X27	OprG	17 (8)	4	4	-	-
11	3BRY	TbuX	27 (14)	4	2	2	-
12	1K24	OpcA	15 (10)	4	3	1	-
13	1UYN	NalP	14 (12)	4	3	-	1
14	1H6S	Porin	19 (16)	4	3	1	-
15	3EMO	Hia	[6 (4)]x3f	1	1	-	-
16	4FQE	KdgM	14 (12)	3	2	-	1
17	1UUN	MspA	[14 (2)]x8f	4	3	1	-
18	3WI4	PorB	[22 (16)]x3f	4	3	-	1
19	1WP1	OprM	[13 (4)]x3f	4	2	-	2
20	2LME	YadA	[5 (4)]x3f	2	1	-	1

^aNon-redundant structures were retrieved from PDBTM: Protein Data Bank of Transmembrane Proteins; http://pdbtm.enzim.hu/. Only proteins with a maximum of four Trp residues are listed.

^bExamples 15-19 have been classified as porins in PDB; 20 is an anchor protein.

^cPDB: RCSB Protein Data Bank; http://www.rcsb.org/pdb.

^dInformation derived from both PDBTM and PDB.

^eNumbers provided represent the total number of β-strands in the structure and those in brackets represent the total number of transmembrane β-strands.

^f[Number of strands in one monomer (Number of transmembrane strands in one monomer)] x Number of monomers.