TABLE 1.

Hydrogen bonding and hydrophobic interactions between sugar and channel lining

Region I				Region II
Hydrogen bonding interactions
Domain	Residue	z	Atom	Domain	Residue	z	Atom
C	Ser-346	−15.9	Hγ,O	C	Glu-269	0.2	Oε
C	Thr-338	−17.1	O	N	Phe-118	1.0	O
N	Asp-68	−18.0	Oδ	N	Met-23	1.8	Sδ
N	Lys-131	−19.0	Hζ	C	His-322	4.6	Nε
C	Val-343	−21.2	O	C	Asp-237	5.0	Oδ
N	Asn-199	−24.9	O	N	Tyr-26	6.6	O
C	Ala-417	−26.6	HN	N	Phe-27	6.9	O
N	Ala-200	−27.2	O	C	Asp-240	8.6	Oδ
N	Ala-198	−28.9	O	C	Lys-319	9.7	Hζ
N	Arg-134	−22.5	Hη	C	Gln-241	10.1	O,Oε
N	Glu-130	−16.2	Oε	N	Phe-30	11.5	HN,O
N	Glu-126	−9.1	Oε	C	Gln-242	14.9	Hε,Nε
N	Arg-144	−7.2	Hη	N	Pro-31	14.0	N
N	Pro-123	−7.7	O	C	Asn-245	18.2	Hδ,Nδ,Oδ
C	Cys-333	−7.6	Hγ,Sγ	N	Lys-42	19.9	Hζ
N	Cys-148	−3.4	Hγ,Sγ	N	Ile-40	19.9	O
C	Asn-272	−2.5	Hδ,Nδ,Oδ	C	Thr-248	20.2	Hγ
N	Asn-119	−1.1	Hδ	N	Asp-36	21.9	Oδ
C	Lys-358	−0.5	Hζ		–	–	–
Hydrophobic interactions
Domain	Residue	z		domain	residue	z
C	Phe-334	−12.8	–	N	Tyr-26	6.6	–
C	Tyr-350	−10.7	–	N	Phe-27	6.9	–
C	Phe-354	−5.7	–	N	Phe-49	10.1	–
N	Phe-118	1.0	–	N	Phe-30	11.5	–
N	Trp-151	1.9	–	C	Phe-261	12.6	–

The list is partitioned into regions I and II covering cytoplasmic and periplasmic half-channels, respectively. For hydrogen bonding interactions, all polar protein side-chain atoms were considered as donors/acceptors along with the amide nitrogen and oxygen atoms of the peptide backbone. For lactose, all hydroxyl groups were considered as donors/acceptors along with the oxygen atom of the 1,4-glycosidic linkage. A hydrogen bond was registered for a donor-acceptor distance ≤3 Å. For hydrophobic interactions distances between any atom of the aromatic ring of residues Phe, Trp, and Tyr and any nonhydrogen atom of sugar were used for assigning an interaction with the same distance cutoff as above. The mean center-of-mass of each residue is given by z (Å). Each residue is assigned to its respective domain (N or C).