Gamma carbonic anhydrases in plant mitochondria

Abstract

Three genes from Arabidopsis thaliana with high sequence similarity to gamma carbonic anhydrase (gammaCA), a Zn containing enzyme from Methanosarcina thermophila (CAM), were identified and characterized. Evolutionary and structural analyses predict that these genes code for active forms of gammaCA. Phylogenetic analyses reveal that these Arabidopsis gene products cluster together with CAM and related sequences from alpha and gamma proteobacteria, organisms proposed as the mitochondrial endosymbiont ancestor. Indeed, in vitro and in vivo experiments indicate that these gene products are transported into the mitochondria as occurs with several mitochondrial protein genes transferred, during evolution, from the endosymbiotic bacteria to the host genome. Moreover, putative CAM orthologous genes are detected in other plants and green algae and were predicted to be imported to mitochondria. Structural modeling and sequence analysis performed in more than a hundred homologous sequences show a high conservation of functionally important active site residues. Thus, the three histidine residues involved in Zn coordination (His 81, 117 and 122), Arg 59, Asp 61, Gin 75, and Asp 76 of CAM are conserved and properly arranged in the active site cavity of the models. Two other functionally important residues (Glu 62 and Glu 84 of CAM) are lacking, but alternative amino acids that might serve to their roles are postulated. Accordingly, we propose that photosynthetic eukaryotic organisms (green algae and plants) contain gammaCAs and that these enzymes codified by nuclear genes are imported into mitochondria to accomplish their biological function.

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

“…3 Based on sequence comparisons, these subunits were initially proposed to be called "ferripyochelin-binding proteins." However, later it became clear that these identifications were based on a falsely annotated data base entry (12). Instead, significant sequence identity was discovered to the prototype ␥-carbonic anhydrase of the Archaebacterium Methanosarcina thermophila (12).…”

“…However, later it became clear that these identifications were based on a falsely annotated data base entry (12). Instead, significant sequence identity was discovered to the prototype ␥-carbonic anhydrase of the Archaebacterium Methanosarcina thermophila (12). Computer modeling using the crystal structure of the archaebacterial ␥-carbonic anhydrase revealed that at least three of the five plant-specific complex I subunits of Arabidopsis have a conserved active site (12).…”

“…Instead, significant sequence identity was discovered to the prototype ␥-carbonic anhydrase of the Archaebacterium Methanosarcina thermophila (12). Computer modeling using the crystal structure of the archaebacterial ␥-carbonic anhydrase revealed that at least three of the five plant-specific complex I subunits of Arabidopsis have a conserved active site (12). They are called carbonic anhydrase 1 (CA1) (At1g19580), CA2 (At1g47260), and CA3 (At5g66510) in Arabidopsis.…”

Reduction of Plastid-Localized Carbonic Anhydrase Activity Results in Reduced Arabidopsis Seedling Survivorship

“…Most recently, EST and gene expression analyses based on the full genome have shown that three of eight a-type sequences are expressed in Arabidopsis, whereas all six of the b-type sequences are represented in the EST database (Fabre et al, 2007). In addition, Parisi et al (2004) identified a family of three g-type sequences in Arabidopsis that are all expressed.…”

Carbonic anhydrases in fungi

“…Similar to S. macrospora, A. thaliana encodes multiple CA isoenzymes that are localized to the cytoplasm, plasma membrane and mitochondria, as well as to chloroplasts (Fabre et al, 2007;Parisi et al, 2004). The major CA of A. thaliana was shown to be the chloroplast-localized AtbCA1 (Ferreira et al, 2008).…”