Molecular and phylogenetic characterization of syntaxin genes from parasitic protozoa.
Vesicular transport is an integral process in eukaryotic cells and the syntaxins, a member of the SNARE protein superfamily, are a critical piece of the vesicular transport machinery. We have obtained syntaxin homologues from diverse protozoan parasites (including Entamoeba, Giardia, Trichomonas and Trypanosoma), determined the paralogue affinity of the homologues by molecular phylogenetics and compared functionally critical amino acid sites identified in other syntaxins. Surprisingly, three sequences deviate at the signature glutamine residue position, conserved in all previously identified syntaxin homologues. It is known that, despite conserved structure and function of both the syntaxins and the proteins of the regulatory SM superfamily, the various syntaxin paralogues bind their respective SM partners at different regions of the syntaxin molecule. These sites of interactions have been identified down to the individual residues. The pattern of conservation at these residues, in our evolutionarily diverse sampling of syntaxin paralogues, is therefore used to gain further insight into the interaction of these proteins. Phylogenetic analysis confirms and extends previous conclusions that the syntaxin families are present in diverse eukaryotes and that the syntaxin sub-families diverged early in eukaryotic evolution. This result is expanded with the inclusion of new homologues for previously sampled taxa, newly sampled taxa, and newly sampled syntaxin sub-families. Because of their integral role in membrane trafficking, the syntaxin genes represent a valuable potential molecular marker for the experimental study of the endomembrane system of disease-causing protists.
Dacks
Joel B
JB
Program in Evolutionary Biology, Department of Biochemistry and Molecular Biology, Dalhousie University, 5850 College Street, Halifax, NS, Canada B3H 1X5. joeld@nhm.ac.uk
Doolittle
W Ford
WF
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D016054:DNA, Protozoan / Q000235:genetics; D004748:Entamoeba histolytica / Q000235:genetics; D056890:Eukaryota / Q000235:genetics*; D019143:Evolution, Molecular; D017125:Genes, Protozoan; D016829:Giardia lamblia / Q000235:genetics; D007438:Introns; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics*; D008969:Molecular Sequence Data; D010802:Phylogeny; D017433:Protein Structure, Secondary; D015800:Protozoan Proteins / Q000737:chemistry / Q000235:genetics*; D050765:Qa-SNARE Proteins; D017386:Sequence Homology, Amino Acid; D014246:Trichomonas vaginalis / Q000235:genetics; D014346:Trypanosoma brucei brucei / Q000235:genetics
D016054:DNA, Protozoan; D008565:Membrane Proteins; D015800:Protozoan Proteins; D050765:Qa-SNARE Proteins