Characterization of thePreprotein and Amino Acid TransporterGene Family in Arabidopsis

Abstract

Seventeen loci encode proteins of the preprotein and amino acid transporter family in Arabidopsis (Arabidopsis thaliana). Some of these genes have arisen from recent duplications and are not in annotated duplicated regions of the Arabidopsis genome. In comparison to a number of other eukaryotic organisms, this family of proteins has greatly expanded in plants, with 24 loci in rice (Oryza sativa). Most of the Arabidopsis and rice genes are orthologous, indicating expansion of this family before monocot and dicot divergence. In vitro protein uptake assays, in vivo green fluorescent protein tagging, and immunological analyses of selected proteins determined either mitochondrial or plastidic localization for 10 and six proteins, respectively. The protein encoded by At5g24650 is targeted to both mitochondria and chloroplasts and, to our knowledge, is the first membrane protein reported to be targeted to mitochondria and chloroplasts. Three genes encoded translocase of the inner mitochondrial membrane (TIM)17-like proteins, three TIM23-like proteins, and three outer envelope protein16-like proteins in Arabidopsis. The identity of Arabidopsis TIM22-like proteins is most likely a protein encoded by At3g10110/At1g18320, based on phylogenetic analysis, subcellular localization, and complementation of a yeast (Saccharomyces cerevisiae) mutant and coexpression analysis. The lack of a preprotein and amino acid transporter domain in some proteins, localization in mitochondria, plastids, or both, variation in gene structure, and the differences in expression profiles indicate that the function of this family has diverged in plants beyond roles in protein translocation.

The direct route: a simplified pathway for protein import into the mitochondrion of trypanosomes

“…A single inner membrane translocase The Tim17-Tim22-Tim23 family of proteins (PFAM: PF02466) [22] are a set of highly-conserved proteins found in animals, plants, fungi and protists that range from Plasmodium to Trichomonas [2,23,24]. In all cases, the protein has four predicted transmembrane domains with specific amino acid signature motifs [23].…”

A Study of New Arabidopsis Chloroplast RNA Editing Mutants Reveals General Features of Editing Factors and Their Target Sites

“…After bombardment, the cells were placed in the dark at 228C for 24 h. Observation of transient GFP and RFP expression was performed using an Olympus BX61 fluorescence microscope with excitation wavelengths of 460/480 nm (GFP) and 535/555 nm (RFP) and emission wavelengths of 495 to 540 nm (GFP) and 570 to 625 nm (RFP). Subsequent images were captured using Cell imaging software as previously described Murcha et al, 2007).…”

The reducible complexity of a mitochondrial molecular machine

“…Bacteria have several amino acid and peptide transporters that could have served as a primitive protein transport channel, and previous sequence analyses have made the case that the mitochondrial protein transport channel Tim23 was derived from LivH-type amino acid transporters (13,27). Here we show that ␣-proteobacteria also have proteins related in sequence to the other 2 ubiquitous components of the TIM23 complex, Tim44 and Tim14.…”

“…The TIM23 complex is specifically responsible for protein transport across the mitochondrial inner membrane. This protein transport machine has been studied in yeast, in plants, and in humans, and is composed of a conserved set of protein subunits that associate together to form the molecular machine (13)(14)(15). Three of the subunits are both found in enough representative groups to suggest they are present in all eukaryotic organisms, and are essential for cell viability in yeast: (i) the Tim23 subunit, a simple transmembrane protein that forms the channel through which protein substrates pass into the mitochondrial matrix; (ii) Tim44, found on the inner face of the mitochondrial membrane where it interacts with both Tim23 and Hsp70, thereby docking the protein import motor to the Tim23 channel; and (iii) the Tim14/ Pam18 subunit that interacts with several proteins in the TIM23 complex and directly stimulates the ATPase activity of Hsp70, thereby activating the motor to drive protein transport (10,(16)(17)(18).…”

“…Protein transport into mitochondria requires the action of the 4 membrane-embedded molecular machines: the TOM, TIM22, TIM23, and SAM complexes (10)(11)(12)(13), each composed of up to 8 distinct protein subunits. However, bacteria do not import proteins across their outer and inner membranes, and the TOM and TIM23 complexes that provide this protein import function to mitochondria do not have counterparts in bacteria.…”