Glucan phosphatases (GPs) regulate starch degradation by dephosphorylating the starch granule.  Historically, GPs have been defined as proteins containing a dual specificity phosphatase (DSP) domain and a carbohydrate binding module (CBM).  To date there are two published GPs:  Starch-Excess-4 (SEX4) and Like-SEX4-1 (LSF1).  Our lab recently determined the structure of SEX4.  These data identified a previously unknown domain in the C-terminus of GPs, the so-called CT-domain.  The discovery of this domain allowed us to identify a third member of the GP family, LSF2.  SEX4 and LSF2 possess different specificities:  SEX4 dephosphorylates starch preferentially at the C6 position of glucose, while LSF2 acts on the C3 position.  We are using the findings from the Arabidopsis GPs to study the homologues in the green alga C.reinhardtii.  In addition to regulating starch degradation, starch phosphorylation is important for its physicochemical properties for industrial uses.  We are in the initial stages of the functional characterization of the algae GPs, and crystallization trials are ongoing.  In vitro assays have shown that purified C. reinhardtii GPs have the ability to bind and dephosphorylate starch.  Characterization of algae GPs will further elucidate the molecular mechanisms in starch degradation and provide the knowledge necessary to engineer starch phosphorylation.

Functional characterization of glucan phosphatases in green algae<i>
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246th National Meeting (2013)

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