Structural Contour Map of the Iota Carbonic Anhydrase from the Diatom Thalassiosira pseudonana Using a Multiprong Approach


  • Jensen Erik
  • Receveur-Brechot Véronique
  • Hachemane Mohand
  • Wils Laura
  • Barbier Pascale
  • Parsiegla Goetz
  • Gontero Brigitte
  • Launay Hélène


  • Analytical ultracentrifugation
  • CO2 concentrating mechanism
  • Diffusion-ordered NMR spectroscopy
  • Electrospray ionization mass spectrometry
  • Homotetramer
  • Manganese
  • Metalloprotein
  • Photosynthesis
  • Small-angle X-ray scattering

document type



Carbonic anhydrases (CAs) are a family of ubiquitous enzymes that catalyze the interconversion of CO2 and HCO3−. The “iota” class (ι-CA) was first found in the marine diatom Thalassiosira pseudonana (tpι-CA) and is widespread among photosynthetic microalgae and prokaryotes. The ι-CA has a domain COG4875 (or COG4337) that can be repeated from one to several times and resembles a calcium–calmodulin protein kinase II association domain (CaMKII-AD). The crystal structure of this domain in the ι-CA from a cyanobacterium and a chlorarachniophyte has been recently determined. However, the three-dimensional organization of the four domain-containing tpι-CA is unknown. Using biophysical techniques and 3-D modeling, we show that the homotetrameric tpι-CA in solution has a flat “drone-like” shape with a core formed by the association of the first two domains of each monomer, and four protruding arms formed by domains 3 and 4. We also observe that the short linker between domains 3 and 4 in each monomer confers high flexibility, allowing for different conformations to be adopted. We propose the possible 3-D structure of a truncated tpι-CA containing fewer domain repeats using experimental data and discuss the implications of this atypical shape on the activity and metal coordination of the ι-CA.

more information