Table 2.

Features of 4JA3 and 4GBY (inward and outward occluded states of XylE, respectively).

Name	Residues in sequence	Location in structure
N-terminal cross	Ile 112-Thr 117	Long loop between TMSs 3–4*
Edge of N-terminal quadrant	Thr 247-Gly 263	Corresponds to third interdomain helical segment
Big blue cross (C-terminal quadrant)	Pro 389-Ala 413	C-terminal 1/3 of TMS10 (“TMS10C”), N-terminal 1/3 of TMS11 (“TMS11N”)**,***
Big red cross (C-terminal quadrant)	Ser 423-Ser 433	C-terminal half of TMS11

^*) This extended loop is not found in LacY.

^**) The TMS10B region contains the E(X₆)R motif located at 397–404, conserved across GLUTs 1–4³. Arg 160-Glu 397 and Glu 153-Arg 404 form interdomain salt bridges that are broken in the inward open state. A third bridge, formed between Glu 397 and Arg 341 is missing in the inward occluded structure but present in the outward occluded and inward open states. Trp 392 forms part of the cytoplasmic lid of the substrate cavity in the outward occluded state³.

^***) Incorrectly identified as being restricted to TMS10B in Quistgaard et al. The differences identified by superimposition are the regions that could be identified from averaged superimposition solutions, and can differ from the more accurate localization of movement observed by using Δ-distance maps.