Putative RuBisCO Activase CfxQ in the Toxic Alga Heterosigma akashiwo

Kun-Lin Lee, Senior, Biochemistry

Amanda Hoyt, Recent Graduate, Biochemistry

Mentor: Rose Ann Cattolico, Department of Biology

CO2 entry in the Calvin Cycle of many autotrophic organisms is driven by the enzyme Ribulose 1,5-Bisphosphate Carboxylase/Oxygenase (RuBisCO). The activity of RuBisCO is catalyzed by an ATP dependent enzyme, RuBisCO Activase. Analysis of the chloroplast-encoded cfxQ in the Raphidophyte Heterosigma akashiwo shows sequence homology to bacterial RuBisCO activases. In addition, previous studies revealed that CfxQ enhances the performance of RuBisCO in bacterial systems. We hypothesize that Heterosigma CfxQ is a RuBisCO Activase.

The cfxQ gene is being studied at three different levels: genomic, transcriptional, and proteomic. At the genomic level, though present in almost 2,500 copies per cell, the presence of single nucleotide polymorphisms (SNPs) has been documented to occur when geographically distinct algal populations were analyzed. Five variants of the cfxQ gene have been identified among nineteen Heterosigma strains that have been sequenced. The nucleotide changes that have been observed cause both synonymous and non-synonymous amino acid alterations in the resulting proteins. At the transcriptional level, RNA isolation and quantitative PCR techniques are being developed to probe the relationship between the expression of cfxQ and the RuBisCO operon over the synchronized growth cycle of Heterosigma. At the proteomic level, we wish to analyze the biochemistry of CfxQ (e.g. ATPase activity; RuBisCO Activase activity.) To achieve this goal, we are presently over-expressing the cfxQ gene in Topo T7 bacterial vector.