title: Quantitative proteomic analysis reveals evolutionary divergence and species-specific peptides in the Alexandrium tamarense complex (Dinophyceae).
abstract: The Alexandrium tamarense/catenella/fundyense complex is the major causative agent responsible for harmful algal blooms and paralytic shellfish poisoning around the world. However, taxonomy of the A. tamarense complex is contentious and the evolutionary relationships within the complex are unclear. This study compared protein profiles of the A. tamarense complex collected from different geographic regions using the two dimensional fluorescence difference gel electrophoresis (2-D DIGE) approach, and identified species-specific peptides using MALDI-TOF/TOF mass spectrometry. The results showed that three Alexandrium morphotypes presented significantly different protein expression patterns with about 30-40% shared proteins. However, ecotypes from different geographic regions within a species exhibited the same expression patterns, although a few proteins were altered in abundance. Several proteins, i.e. ribulose-1,5-bisphosphate carboxylase oxygenase form II, plastid protein NAP50, methionine S-adenosyltransferase, and peridinin-chlorophyll a-binding protein, were identified and presented different shift patterns in isoelectric point and/or molecular weight in the 2-D DIGE gels, indicating that amino acid mutation and/or posttranslational modification of these proteins had occurred. The species-specific peptide mass fingerprint and amino acid sequence of ribulose-1,5-bisphosphate carboxylase oxygenase were characterized in the A. tamarense complex, and amino acid substitution occurred among them. This study indicated that evolutionary divergence had occurred at the proteomic level in the A. tamarense complex, and that the species-specific peptides could be used as potential biomarkers to distinguish the three morphotypes.
  
  
  CONCLUSIONS
  Scientific question: The Alexandrium tamarense/catenella/fundyense complex is the major causative agent responsible for harmful algal blooms and paralytic shellfish poisoning around the world. However, taxonomy of the A. tamarense complex is contentious and the evolutionary relationships within the complex are unclear, which has seriously impeded our understanding of Alexandrium-causing HABs and, consequently, the monitoring, mitigation and prevention. Technical significance: This study, for the first time, compared the global protein expression patterns of eight ecotypes from the A. tamarense complex and identified species-specific peptides using a quantitative proteomic approach combining 2-D DIGE and MALDI-TOF/TOF MS.
  
  
  CONCLUSIONS
  This study demonstrated that the evolutionary divergence had occurred in the A. tamarense complex at the proteomic level, and the complex should be classified into three species, i.e. A. tamarense, A. catenella, and A. fundyense. Moreover, the species-specific peptide mass fingerprints could be used as potential biomarkers to distinguish the three morphotypes.
authors.affiliation: State Key Laboratory of Marine Environmental Science/College of the Environment and Ecology, Xiamen University, Xiamen 361005, China.
authors.forename: Cheng
authors.initials: C
authors.lastname: Li
authors.forename: Yong
authors.initials: Y
authors.lastname: Zhang
authors.forename: Zhang-Xian
authors.initials: ZX
authors.lastname: Xie
authors.forename: Zhi-Ping
authors.initials: ZP
authors.lastname: He
authors.forename: Lin
authors.initials: L
authors.lastname: Lin
authors.forename: Da-Zhi
authors.initials: DZ
authors.lastname: Wang
mesh_terms: D000595:Amino Acid Sequence; D005075:Biological Evolution; D015415:Biomarkers / Q000378:metabolism; D002338:Carotenoids / Q000235:genetics; D004141:Dinoflagellida / Q000145:classification / Q000235:genetics*; D015180:Electrophoresis, Gel, Two-Dimensional; D057097:Harmful Algal Bloom; D007526:Isoelectric Point; D008387:Marine Toxins / Q000235:genetics; D008716:Methionine Adenosyltransferase / Q000235:genetics; D008970:Molecular Weight; D040901:Proteomics / Q000379:methods; D015800:Protozoan Proteins / Q000235:genetics*; D012273:Ribulose-Bisphosphate Carboxylase / Q000235:genetics*; D057096:Shellfish Poisoning / Q000235:genetics; D013045:Species Specificity; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D015415:Biomarkers; D008387:Marine Toxins; D015800:Protozoan Proteins; C073227:peridinin chlorophyll-a protein, Dinophyceae; D002338:Carotenoids; D008716:Methionine Adenosyltransferase; D012273:Ribulose-Bisphosphate Carboxylase