A third of the yeast mitochondrial proteome is dual localized: a question of evolution.

There are a growing number of examples of identical or almost identical proteins, which are localized to two (or more) separate compartments, a phenomenon that is termed protein dual localization, dual distribution or dual targeting. We previously divided a reference set of known yeast mitochondrial proteins into two groups, suggested to be dual localized or exclusive mitochondrial proteins. Here we examined this evaluation by screening 320 mitochondrial gene products for dual targeting, using the α-complementation assay. The analysis of the results of this experimentally independent screen supports our previous evaluation that dual localized mitochondrial proteins constitute a subgroup of mitochondrial proteins with distinctive properties. These proteins are characterized by a lower probability of mitochondrial localization (MitoProtII score), a lower net charge and are enriched for proteins with a weaker mitochondrial targeting sequence. Conversely, mRNAs of exclusive mitochondrial proteins are enriched in polysomes associated with mitochondria. Based on the discovery of more than 60 new gene products that are now assumed to be dual targeted, we have updated an annotation list of dual-targeted proteins. We currently estimate that more than a third of the mitochondrial proteome is dual targeted, and suggest that this abundant dual targeting presents an evolutionary advantage.

Dual targeted mitochondrial proteins are characterized by lower MTS parameters and total net charge.

BACKGROUND: In eukaryotic cells, identical proteins can be located in different subcellular compartments (termed dual-targeted proteins). METHODOLOGY/PRINCIPAL FINDINGS: We divided a reference set of mitochondrial proteins (published single gene studies) into two groups: i) Dual targeted mitochondrial proteins and ii) Exclusive mitochondrial proteins. Mitochondrial proteins were considered dual-targeted if they were also found or predicted to be localized to the cytosol, the nucleus, the endoplasmic reticulum (ER) or the peroxisome. We found that dual localized mitochondrial proteins have i) A weaker mitochondrial targeting sequence (MitoProtII score, hydrophobic moment and number of basic residues) and ii) a lower whole-protein net charge, when compared to exclusive mitochondrial proteins. We have also generated an annotation list of dual-targeted proteins within the predicted yeast mitochondrial proteome. This considerably large group of dual-localized proteins comprises approximately one quarter of the predicted mitochondrial proteome. We supported this prediction by experimental verification of a subgroup of the predicted dual targeted proteins. CONCLUSIONS/SIGNIFICANCE: Taken together, these results establish dual targeting as a widely abundant phenomenon that should affect our concepts of gene expression and protein function. Possible relationships between the MTS/mature sequence traits and protein dual targeting are discussed.

Spin Transition in a Manganese(III) Porphyrin Cation Radical, Its Transformation to a Dichloromanganese(IV) Porphyrin, and Chlorination of Hydrocarbons by the Latter.

Chemical oxidation of (TMP)Mn(III)(Cl) (TMP = the tetramesitylporphyrinato dianion) by Fe(ClO(4))(3) leads to the porphyrin-oxidized product (TMP(*)(+))Mn(III)(ClO(4))(2). Magnetic measurements and EPR spectroscopy show that the total spin of the complex changes from S = (5)/(2) at high temperature to S = (3)/(2) at low temperature. Ligand exchange of the perchlorato ligands in (TMP(*)(+))Mn(III)(ClO(4))(2) by chloride anions is accompanied by a change of the oxidation site from porphyrin to metal, resulting in (TMP)Mn(IV)(Cl)(2). This high-valent-metal complex can effect chlorine atom transfer to olefins, as well as to dimedone and chlorodimedone, natural substrates of chloroperoxidases.