RESUMO
The obligate intracellular parasitic bacteria rickettsiae are more closely related to mitochondria than any other microbes investigated to date. A rickettsial putative peptidase (RPP) was found to resemble the alpha and beta subunits of mitochondrial processing peptidase (MPP), which cleaves the transport signal sequences of mitochondrial preproteins. RPP showed completely conserved zinc-binding and catalytic residues compared with beta-MPP but barely contained any of the glycine-rich loop region characteristic of alpha-MPP. When the biochemical activity of RPP purified from a recombinant source was analyzed, RPP specifically hydrolyzed basic peptides and presequence peptides with frequent cleavage at their MPP-processing sites. Moreover, RPP appeared to activate yeast beta-MPP so that it processed preproteins with shorter presequences. Thus, RPP behaves as a bifunctional protein that could act as a basic peptide peptidase and a somewhat regulatory protein for other protein activities in rickettsiae. These are the first biological and enzymological studies to report that a protein from a parasitic microorganism can cleave the signal sequences of proteins targeted to mitochondria.
Assuntos
Proteínas de Bactérias/metabolismo , Mitocôndrias/metabolismo , Proteínas Mitocondriais/metabolismo , Rickettsia prowazekii/metabolismo , Sequência de Aminoácidos , Proteínas de Bactérias/química , Proteínas de Bactérias/genética , Cinética , Metaloendopeptidases/química , Metaloendopeptidases/genética , Metaloendopeptidases/metabolismo , Proteínas Mitocondriais/genética , Dados de Sequência Molecular , Peptídeos/química , Peptídeos/metabolismo , Filogenia , Sinais Direcionadores de Proteínas , Estrutura Secundária de Proteína , Estrutura Terciária de Proteína , Transporte Proteico , Proteínas Recombinantes de Fusão/genética , Proteínas Recombinantes de Fusão/metabolismo , Rickettsia prowazekii/genética , Alinhamento de Sequência , Peptidase de Processamento MitocondrialRESUMO
We report here the isolation of 44 genes that are upregulated after serum starvation and/or contact inhibition. These genes have been termed TIGA, after Transcript Induced by Growth Arrest. We found that there are two kinds of G0 phases caused by serum starvation, namely, the shallow G0 (or G0/G1) and the deep G0 phases. The shallow G0 is induced by only a few hours of serum starvation, while deep G0 is generated after 3 days of serum starvation. We propose that mammalian cells enter deep G0 through a G0 gate, which is only opened on the third day of serum starvation. TIGA1, one of the uncharacterized TIGA genes, encodes a homolog of cyanate permease of bacteria and localizes in mitochondria. This suggests that Tiga1 is involved in the inorganic ion transport and metabolism needed to maintain the deep G0 phase. Ectopic expression of TIGA1 inhibited not only tumor cell proliferation but also anchorage-independent growth of cancer cell lines. A microsatellite marker, ENDL-1, allowed us to detect loss of heterozygosity around the TIGA1 gene region (5q21-22). Further analysis of the TIGA genes we have identified here may help us to better understand the mechanisms that regulate the G0 phase.
