M2 internship – CO2 concentration mechanism in diatoms

Atypical Carbonic Anhydrase in the CO2 concentration mechanism of the diatom
Thalassiosira pseudonana

Supervisors: Hélène Launay (), Brigitte Gontero (), BIP2

Diatoms are members of a divergent branch of micro-algae with a complex evolutionary history. They possess complex CO2 concentration mechanisms (CCM) that are highly efficient to transport inorganic carbon into their 4-membranes chloroplast. We have identified and structurally characterise a Carbonic Anhydrase (CA) of a new class (ι-CA), that has an important role in the CCM of the diatom Thalassiosira pseudonana, and that is localised in the chloroplast boundary. Since our initial publication, other ι-CAs have been identified from prokaryotes, cyanobacteria and micro-algae. They possess unusual properties for CA:

  • They are not metal-dependent, or have unusual metal co-factor (such as Mn for T. pseudonana ι-CA).
  • They have unusual domain repetition (four domains repetition for T. pseudonana ι-CA).
  • They have unusual structural organisation with complex arrangement (drone-like structure for T. pseudonana ι-CA).

We propose a 6 months internship on the study of T. pseudonana ι-CA. The student will pursue our enzymatic characterisation of the enzyme with activity assay (CO2 ↔ HCO3 reversible conversions and esterase activity) on different constructions of the proteins (already available) with and without metal co-factor. Besides, the effect of the metal ion on some physiological properties (growth rates, photosynthetic parameters in relation to ι-CA expression) of T. pseudonana will be studied. In parallel, photosynthetic efficiency under a range of growth conditions (high or low [CO2], high or low light) will be determined.

1. Jensen, E. L. et al. Structural contour map of the iota carbonic anhydrase from the diatom Thalassiosira pseudonana using a multiprong approach. International Journal of Molecular Sciences 22, 8723 (2021).
2. Jensen, E. L., Clement, R., Kosta, A., Maberly, S. C. & Gontero, B. A new widespread subclass of carbonic anhydrase in marine  phytoplankton. ISME J 13, 2094–2106 (2019).
3. Jensen, E., Clément, R., Maberly, S. C. & Gontero, B. Regulation of the Calvin-Benson-Bassham cycle in the enigmatic diatoms: biochemical and evolutionary variations on an original theme. Philos. Trans. R. Soc. Lond., B, Biol. Sci. 372, (2017).
4. Clement, R., Dimnet, L., Maberly, S. C. & Gontero, B. The nature of the CO2 -concentrating mechanisms in a marine diatom, Thalassiosira pseudonana. New Phytol. 209, 1417–1427 (2016).

Contacts: Hélène LAUNAY, Brigitte GONTERO

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