Carbonic Anhydrase Subunits Form a Matrix-exposed Domain Attached to the Membrane Arm of Mitochondrial Complex I in Plants

Abstract

Complex I of Arabidopsis includes five structurally related subunits representing ␥-type carbonic anhydrases termed CA1, CA2, CA3, CAL1, and CAL2. The position of these subunits within complex I was investigated. Direct analysis of isolated subcomplexes of complex I by liquid chromatography linked to tandem mass spectrometry allowed the assignment of the CA subunits to the membrane arm of complex I. Carbonate extraction experiments revealed that CA2 is an integral membrane protein that is protected upon protease treatment of isolated mitoplasts, indicating a location on the matrix-exposed side of the complex. A structural characterization by single particle electron microscopy of complex I from the green alga Polytomella and a previous analysis from Arabidopsis indicate a plant-specific spherical extra-domain of about 60 Å in diameter, which is attached to the central part of the membrane arm of complex I on its matrix face. This spherical domain is proposed to contain a heterotrimer of three CA subunits, which are anchored with their C termini to the hydrophobic arm of complex I. Functional implications of the complex I-integrated CA subunits are discussed.

The mitochondrial respiratory chain of the secondary green alga Euglena gracilis shares many additional subunits with parasitic Trypanosomatidae

“…However, in the present study, no evidence for the presence of CIII or CIV subunits could be obtained in the band corresponding to CI in E. gracilis. Compared with CI in fungi and mammals, CI in green plants (Cardol et al, 2004;Sunderhaus et al, 2006), amoeba, and presumably other eukaryotes (Gawryluk and Gray, 2010) comprises additional subunits belonging to the carbonic anhydrase (CAG) protein family. Two CAG proteins have also been specifically identified in CI of E. gracilis.…”

The Cytoplasmic Carbonic Anhydrases βCA2 and βCA4 Are Required for Optimal Plant Growth at Low CO2

“…The active unit of the bCA is a dimer where the active site is located at the interface of the two monomers (Kimber and Pai, 2000). In contrast, gCAs are trimers that have their active site zinc ion situated at the interface of two subunits coordinated by His residues from both subunits (Kisker et al, 1996;Iverson et al, 2000).In Arabidopsis (Arabidopsis thaliana), there are three gCA proteins and two g-like proteins that interact to form an extra structure of complex I of the mitochondrial electron transport chain (Perales et al, 2004;Sunderhaus et al, 2006). Although not active in vitro, gCA has been shown to bind inorganic carbon (Martin et al, 2009), affect complex I levels, plant growth, and gas-exchange rates when deleted (Perales et al, 2004;Soto et al, 2015), and cause plant sterility when ectopically overexpressed ).…”

“…In Arabidopsis (Arabidopsis thaliana), there are three gCA proteins and two g-like proteins that interact to form an extra structure of complex I of the mitochondrial electron transport chain (Perales et al, 2004;Sunderhaus et al, 2006). Although not active in vitro, gCA has been shown to bind inorganic carbon (Martin et al, 2009), affect complex I levels, plant growth, and gas-exchange rates when deleted (Perales et al, 2004;Soto et al, 2015), and cause plant sterility when ectopically overexpressed ).…”

Respiratory-deficient mutants of the unicellular green alga Chlamydomonas: A review

“…Legends of figures attached to the central part of membrane arm [13]. In Chlamydomonas mutants, two subcomplexes of 700 kDa and 250 kDa have been identified [47].…”

“…Single particle electron microscopy analyzes of complex I from Polytomella (a chloroplast-less and close relative of Chlamydomonas), A. thaliana, Zea mays and Solanum tuberosum indicate that these γ-CA subunits could constitute a spherical domain attached to the central part of the membrane arm of complex I, and exposed to the matrix (Fig. 1A) [10][11][12][13].…”