Abstract
BackgroundProteins of the major intrinsic protein (MIP) family, or aquaporins, have been detected in almost all organisms. These proteins are important in cells and organisms because they allow for passive transmembrane transport of water and other small, uncharged polar molecules.ResultsWe compared the predicted amino acid sequences of 20 MIPs from several algae species of the phylum Heterokontophyta (Kingdom Chromista) with the sequences of MIPs from other organisms. Multiple sequence alignments revealed motifs that were homologous to functionally important NPA motifs and the so-called ar/R-selective filter of glyceroporins and aquaporins. The MIP sequences of the studied chromists fell into several clusters that belonged to different groups of MIPs from a wide variety of organisms from different Kingdoms. Two of these proteins belong to Plasma membrane intrinsic proteins (PIPs), four of them belong to GlpF-like intrinsic proteins (GIPs), and one of them belongs to a specific MIPE subfamily from green algae. Three proteins belong to the unclassified MIPs, two of which are of bacterial origin. Eight of the studied MIPs contain an NPM-motif in place of the second conserved NPA-motif typical of the majority of MIPs. The MIPs of heterokonts within all detected clusters can differ from other MIPs in the same cluster regarding the structure of the ar/R-selective filter and other generally conserved motifs.ConclusionsWe proposed placing nine MIPs from heterokonts into a new group, which we have named the LIPs (large intrinsic proteins). The possible substrate specificities of the studied MIPs are discussed.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-173) contains supplementary material, which is available to authorized users.
Highlights
Proteins of the major intrinsic protein (MIP) family, or aquaporins, have been detected in almost all organisms
We show that MIPs from heterokonts belong to different subfamilies, and nine of them merge into a new Large intrinsic protein (LIP) subfamily, which is closely related with the Small basic intrinsic protein (SIP) subfamily [32] and the MIPC subfamily [33]
Search for homologues in the MIP data base (MIPdb) We used the MIPdb to find homologues of the 20 MIPs from heterokonts. This database contains 8429 MIPs belonging to 11 groups: 577 Aquaporin of eukaryotes (AQPe), 1150 Aquaporin of prokaryotes (AQPp), 363 Aquaglyceroporin of eukaryotes (GLAe), 1827 Aquaglyceroporin of prokaryotes (GLAp), 1052 Glycerol uptake facilitator of prokaryotes (GLPp), 192 Nodulin 26-like intrinsic protein (NIP), 661 Plasma membrane intrinsic protein (PIP), 42 SIPs, and 375 Tonoplast intrinsic protein (TIP), as well as 1053 predicted MIPs
Summary
Proteins of the major intrinsic protein (MIP) family, or aquaporins, have been detected in almost all organisms. These proteins are important in cells and organisms because they allow for passive transmembrane transport of water and other small, uncharged polar molecules. The major intrinsic proteins (MIPs) [1], or aquaporins [2], allow for the passive transmembrane transport of water and other small, uncharged polar molecules [3]. The topology of MIPs resembles a sandwich, consisting of six transmembrane α-helical strands (denoted H1 through H6). These strands are connected to each other by five loops (denoted LA through LE). The LB and LE loops analysis for a majority of MIPs which are considered in the present study
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