SLC classification: an update.

The 386 human SLC superfamily members are diverse in sequence, structure, and function. Using sequence similarity, we previously classified the SLC superfamily members and identified relationships among families. With the recent determination of new SLC structures and identification of previously unknown human SLC families, an update of our previous classification is timely. Here, we comprehensively compare the SLC sequences and structures and discuss the applicability of structure-based ligand discovery to key SLC members.