D364 Nucleic Acids Research, 2012, Vol. 40, Database issue Figure 1. Screenshot of a representative MIP protein, human aquaporin 1. Information about gene structure, substitutions in NPA motif, residues forming the ar/R selectivity ﬁlter, sequence similarity with the templates, RMSD calculated for the modeled structure with the three template structures are some of the features reported for a given MIP in the protein page. NPA motif occur in 74 examples. In 82 cases, substitutions are found only in the second NPA. Both NPA motifs are substituted in 63 MIPs (Table 1). In total, substitutions in at least one of the NPA motifs are found in about 22% of the total MIPs in our data set. Majority of the substitu- tions involve mutation of either Pro or Ala of NPA motif. Only a handful of examples (less than 16) are found in which Asn is mutated indicating its important role in both in structure as a helix capping residue and function as a residue responsible for cation exclusion as demonstrated in recent studies (60). DATA FROM MIP STRUCTURAL MODELS Structure-based data includes the atomic model obtained using the homology modeling procedure, residues that form the ar/R selectivity ﬁlter, structure-based sequence alignment, conservation of residues at the helix–helix inter- face and the HOLE radius proﬁle. The structure-based details also include the root mean square deviation (RMSD) calculated for the modeled MIP and each of the template structure using the program DALI (61). The superposed ﬁgures are available in two different orien- tations (Figure 2A). Many MIPs have long N- and C-terminal extensions and hence the start and end pos- itions of the polypeptide segment used in the homology modeling method are given. Aromatic/arginine selectivity ﬁlter Four residues form the outer constriction nearly 8 A˚ from the conserved NPA motif toward the extracellular side. These residues are contributed by second and ﬁfth TM