Formylation-independent eubacterial protein initiation

起始剂甲硫氨酰-tRNA用于起始古细菌和真核生物细胞质中的蛋白质合成。 相比之下，真细菌和某些真核细胞器（如线粒体和叶绿体）中的蛋白质合成可以使用引发剂甲酰基-甲硫氨酰基-tRNA（fMet-tRNAfMet）启动。 甲酰化对起始剂甲硫氨酰-tRNA（Met-tRNAfMet）具有特异性，并由甲硫氨酰-tRNA甲酰基转移酶（MTF）催化。早期的体外和体内研究导致人们普遍认为Met-tRNAfMet的降解是所有真细菌中蛋白质合成起始的关键步骤。 这一观点得到了以下发现的支持，即在大肠杆菌中破坏MTF基因。coli，S. pneumoniae和B. B.枯草芽孢杆菌严重地减少了细胞生长，并且MTF基因存在于迄今为止测序的所有真细菌基因组中。 然而，这种真细菌蛋白质起始的教条不再有效，因为一些细菌已经显示出独立于细菌的蛋白质合成。我的实验室是第一个证明真细菌，铜绿假单胞菌，有能力使用Met-tRNAfMet启动蛋白质合成。 随后，证明了Met-tRNAfMet的酶解对于S中的蛋白质起始也不是必需的。aureus，H.流感病毒和酿酒酵母线粒体在一定的生长条件下。 因此，与E. coli，S. pneumoniae和B. B.枯草杆菌、铜绿假单胞菌、S. aureus和H.流感病毒可以用fMet-tRNAfMet或Met-tRNAfMet进行起始。 然而，允许在这些细菌中利用Met-tRNAfMet的蛋白质起始的机制尚不清楚。 此外，为什么一些细菌具有用fMet-tRNAfMet和Met-tRNAfMet启动蛋白质合成的能力，而另一些细菌仅用fMet-tRNAfMet启动蛋白质合成的能力尚不清楚。 我们研究的主要目标是（1）理解为什么有些细菌有能力在不依赖β-内酰胺酶的情况下启动蛋白质合成，而其他细菌则依赖β-内酰胺酶，以及（2）鉴定其他不依赖β-内酰胺酶启动蛋白质的真细菌。

The initiator methionyl-tRNA is used to initiate protein synthesis in archaebacteria and the cytoplasm of eukaryotes.  In contrast, protein synthesis in eubacteria and in certain eukaryotic organelles, such as mitochondria and chloroplasts, can be initiated using the initiator formyl-methionyl-tRNA (fMet-tRNAfMet).  Formylation is specific for the initiator methionyl-tRNA (Met-tRNAfMet) and is catalyzed by methionyl-tRNA formyltransferase (MTF). Early studies in vitro and in vivo led to the general belief that formylation of the Met-tRNAfMet is a key step in initiation of protein synthesis in all eubacteria.  This view was reinforced by the findings that disruption of the MTF gene in E. coli, S. pneumoniae and B. subtilis severely curtailed cell growth and the MTF gene is present in all eubacterial genomes sequenced to date.  However, this dogma of eubacterial protein initiation is no longer valid, since some bacteria have been shown to initiate protein synthesis independently of formylation. My laboratory was the first to demonstrate that a eubacteria, Pseudomonas aeruginosa, has the capacity to use Met-tRNAfMet to initiate protein synthesis.  Subsequently, it was demonstrated that formylation of Met-tRNAfMet was not necessary either for protein initiation in S. aureus, H. influenzae and Saccharomyces cerevisiae mitochondria under certain growth conditions.  Thus, unlike E. coli, S. pneumoniae and B. subtilis, which are dependent on fMet-tRNAfMet for protein initiation, P. aeruginosa, S. aureus, and H. influenzae can perform initiation with either fMet-tRNAfMet or Met-tRNAfMet.  The mechanism, however, that allows utilization of Met-tRNAfMet in protein initiation in these bacteria is not understood.  Furthermore, why some bacteria have the ability to initiate protein synthesis with both fMet-tRNAfMet and Met-tRNAfMet and others with only fMet-tRNAfMet is not understood.  The main goals of our research are to (1) understand why some bacteria have the ability to initiate protein synthesis without formylation while others rely on formylation, and (2) identify other eubacteria that are not dependent on formylation for protein initiation.