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Fig. 2 | BMC Plant Biology

Fig. 2

From: An extracellular cation coordination site influences ion conduction of OsHKT2;2

Fig. 2

Localization and conservation of extracellular cation coordination site. a OsHKT2;2 is displayed as transparent surface representation with the selectivity filter and surrounding residues marked in the center of the channel as red surface representation. The cation coordination site is marked on the outer extracellular edge of the protein also as red surface representation, and the position of the four contributing residues is shown. The approximate distance between coordination site and pore is indicated in the top view representation. Detailed position of coordination site forming residues is illustrated on the right in the cartoon representation of OsHKT2;2. The four MPM units with their respective transmembrane (M) and pore domains (P) as well as P71, D75, D501 and K504 are marked. b An extract of the multiple sequence alignment of all eight HKT members present in Oryza sativa. Conservation of the residues P71, D75, D501 and K504 forming the coordination site is indicated. ConSurf grades were calculated on the basis of a multiple sequence alignment of 20 experimentally characterized HKT sequences, and are shown below the sequence alignment. The grades range from 1 (variable) to 9 (conserved) [29]. D75 and K504 are 100% conserved (ConSurf grade 9). P71 is in 90% of HKT sequences conserved (ConSurf grade 8), and contains in 5% of the sequences a lysine or serine. At position 501 a negative charge is somewhat conserved as aspartic in 60% of the sequences (ConSurf grade 4) or glutamic acid (in 15% of the sequences). In the remaining 25% of the sequences, this position holds an asparagine (10%), proline (5%), lysine (5%), or tryptophan (5%). Amino acid sequences used for this analysis are the following: AtHKT1 (Q84TI7), EcHKT1;1 (Q9LLM4), EcHKT1;2 (Q9FVK0), HvHKT2;1 (Q4VWZ3), McHKT1;1 (Q84UZ6), OsHKT1;1 (Q7XPF8), OsHKT1;3 (Q6H501), OsHKT1;4 (Q7XPF7), OsHKT1;5 (Q0JNB6), OsHKT2;1 (Q0D9S3), OsHKT2;2 (Q93XI5), OsHKT2;3 (Q8L481), OsHKT2;4 (Q8L4K5), PhaHKT2;1 (AB234305), PutHKT2;1 (C7B119), SlHKT1;1 (CCJ09641), SlHKT1;2 (CCJ09642), TaHKT1;4 (A0N0D7), TaHKT1;5 (A6XCE1), TaHKT2;1 (Q41515)

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