Table 2.
Selectivity filters and NPA-boxes
| Ar/R selectivity filtera | NPA motifs | |||||||
|---|---|---|---|---|---|---|---|---|
| Subfamily | Proteinb | H2 | H5 | LE1 | LE2 | Loop B | Loop E | Substrate specificity |
| MIPA | CcMIPA1;1 | H | M | M | R | NPM | NPA | |
| AtTIP2;1 | H | I | G | R | NPA | NPA | water [58], urea [59], ammonia [60] | |
| MIPB | OlMIPB1;1 | Y | L | G | R | NPS | NAA | |
| OrMIPB1;1 | Y | F | G | R | NPS | NAA | ||
| GLALlac | Y | V | P | R | NPA | NPA | water, glycerol [25] | |
| MIPC | MpMIPC1;1 | L | C | G | V | NPT | NPA | |
| MrMIPC1;1 | I | T | G | V | NPT | NPA | ||
| OtMIPC1;1 | V | M | C | P | NPV | NPS | ||
| ZmSIP2;1c | S | H | G | S | NPL | NPA | none [61] | |
| OsNIP2;1c | G | S | G | R | NPA | NPA | silicic acid [62], arsenite, antimonite [63] | |
| MIPD | VcMIPD1;1 | N | A | A | R | NPA | NPA | |
| CcMIPD1;1 | N | A | A | R | NPA | NPA | ||
| CnMIPD1;1 | N | A | A | R | NPA | NPA | ||
| CrMIPD1;1 | N | A | A | R | NPA | NPA | glycerol [15] | |
| VcMIPD2;1 | T | L | S | R | NPA | NPA | ||
| CrMIPD2;1 | T | L | S | R | NPL | NPA | ||
| CcMIPD3;1 | S | T | A | R | NPA | NPA | ||
| VcMIPD4;1 | N | A | T | H | NPT | NPA | ||
| OsTIP4;1 | T | T | A | R | NPA | NPA | water, glycerol [29] | |
| MIPE | OrMIPE1;1 | F | H | C | R | NPA | NPA | |
| CnMIPE1;1 | F | H | C | R | NPA | NPA | ||
| CnMIPE1;2 | A | H | C | R | NAA | NPT | ||
| CnMIPE1;3 | F | H | C | R | NPA | NPA | ||
| HsAQP5 | F | H | C | R | NPA | NPA | water [34] | |
| PIP | CcPIP4;1 | F | H | C | R | NPA | NPA | |
| CcPIP4;2 | F | H | C | R | NPA | NPA | ||
| AtPIP2;3 | F | H | T | R | NPA | NPA | water [64] | |
| GIP | PbcvMT325GIP1;1 | F | V | I | R | NPA | NPA | |
| CcGIP1;1 | F | L | N | R | NPA | NPA | ||
| CnGIP1;1 | F | I | I | R | NPA | NPA | ||
| PpGIP1;1 | F | V | P | R | NPA | NPA | glycerol [24] | |
a) The ar/R filter is defined by four amino acid residues: one in helix 2, one in helix 5 and two in loop E b) Protein names written in bold are MIPs with studied substrate specificities used as reference. They are chosen based on the similarity of their ar/R filter to the ar/R filters of the members within the group c)The MIPCs have very diverse ar/R filters, making it hard to find a reference. Therefore two MIPs with ar/R filters somewhat similar to those of the MIPCs are displayed.