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

authors

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

keywords

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

document type

abstract

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.

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