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Novel syntaxin gene sequences from Giardia, Trypanosoma and algae: implications for the ancient evolution of the eukaryotic endomembrane system

Program in Evolutionary Biology, Canadian Institute for Advanced Research, Department of Biochemistry and Molecular Biology, Dalhousie University, Halifax, N.S., B3H 4H7, Canada.

View larger version (47K): [in a new window]   Fig. 1. Global unrooted phylogeny of syntaxin paralogs. This figure illustrates the basic resolution of syntaxin paralogs into five families of varying support and placement of new syntaxin sequences provided by this study (shown in bold). Support values for critical nodes are shown in the inset table with ProtML RELL values/Quartet Puzzling values/Puzzleboot values. For clarity and because internal relationships of the sub-families are more rigorously tested in later analyses, internal nodes for the clades are simply denoted with an asterisk if the ProtML RELL support is greater than 50%. The dashed line linking the fungal endosomal syntaxins to the metazoan and plants ones denotes that all endosomal syntaxins were monophyletic in consensus trees, but did not appear so in the single best tree. Coloured boxes denote the different syntaxin paralog families, with syntaxin PM homologs in red, endosomal homologs in purple, TLG2/syntaxin 16 homologs in blue, syntaxin 6 in green and syntaxin 5 in yellow.

View larger version (49K): [in a new window]   Fig. 2. Unrooted syntaxin PM phylogeny. This data set of 24 taxa and 112 positions shows the two independent evolutionary diversifications of syntaxin paralogs involved in Golgi to plasma membrane transport. The syntaxins derived from the animal diversification are enclosed in the pink box, while the ones in the higher land plant diversification are contained in the orange box. Values for ProtML RELL, Quartet Puzzling and Puzzleboot are shown at all nodes supported over 50% by at least one method. Bracket A shows the separation of syntaxin 1 homologs, while bracket B shows the separation of syntaxins 1, 2 and 3 from syntaxin 4 sequences. New syntaxin sequences provided by this study are shown in bold.

View larger version (40K): [in a new window]   Fig. 3. Unrooted phylogeny of syntaxins 5, 16 and endosomal syntaxins. This phylogeny illustrates the robust reconstruction of the syntaxin 5 family as well as the moderate support for the syntaxin 16 family based on analysis of 18 taxa and 123 positions. The dashed line indicates taxa that were united in the consensus of the methods, but not in the single optimal topology. Support values for nodes with better than 50% support by at least one method are shown (ProtML RELL, Quartet Puzzling and Puzzleboot). The different families are enclosed in boxes according to the colours in Fig. 1. New syntaxin sequences provided by this study are shown in bold.

View larger version (55K): [in a new window]   Fig. 4. Aligned functional regions for syntaxins. This figure illustrates representative syntaxin homologs from evolutionarily diverse eukaryotes aligned in regions containing identified functional residues. (A) Region of the SNARE motif including the epimorphin region, which corresponds to positions 205-246 of R. norvegicus Syn1A. Aa shows the universally conserved Gln residue characteristic of syntaxins. Ab shows the identified Ile 236 residue from syntaxin 1A shown to be important for nSec1—syntaxin 1A complex formation. Ac and Ad underline the identified residues involved in Ca2+ channel interactions with syn1. (B) Botulism toxin binding region from syntaxin PM homologs, which corresponds to positions 162-170 of R. norvegicus Syn1A. Ba and Bb show the two residues also identified to be important for nSec1—syntaxin complex formation.