Recombinant Photorhabdus luminescens subsp. laumondii tRNA dimethylallyltransferase (miaA)

Introduction to Recombinant Photorhabdus luminescens subsp. laumondii tRNA Dimethylallyltransferase (MiaA)

Recombinant Photorhabdus luminescens subsp. laumondii tRNA dimethylallyltransferase, commonly referred to as MiaA, is an enzyme that catalyzes a crucial step in tRNA modification within the bacterium Photorhabdus luminescens subsp. laumondii . Photorhabdus luminescens is an entomopathogenic bacterium known for its symbiotic relationship with nematodes, which together infect and kill insect larvae . MiaA plays a vital role in modifying tRNA by catalyzing the transfer of a dimethylallyl moiety to adenosine at position 37 (A37) on the tRNA molecule . This modification is essential for maintaining the structural integrity and functional efficiency of tRNA, thereby influencing protein synthesis and various cellular processes .

Function and Significance of MiaA

The primary function of MiaA is to catalyze the first step in a two-step tRNA modification process . Specifically, MiaA is responsible for the addition of an isopentenyl group to tRNA . This modification is critical for:

• Regulation of RpoS Expression: The miaA mutation affects RpoS expression, with miaA mutants displaying a defect in β-galactosidase activity and reduced RpoS protein levels . RpoS is a global regulator involved in stress response and stationary phase adaptation in bacteria.

• Maintenance of Symbiotic Relationships: Photorhabdus luminescens maintains symbiotic relationships with nematodes, requiring the production of secondary metabolites . The global post-transcriptional regulator, Hfq, affects this relationship .

• tRNA Stability and Decoding Accuracy: MiaA-mediated modifications contribute to the structural stability of tRNA and ensure accurate decoding during protein synthesis.

MiaA in Escherichia coli

In Escherichia coli, MiaA catalyzes the synthesis of isopentenyladenosine (i6A) at position 37 of tRNAs that read codons starting with uridine . The miaA gene is essential for cell viability in E. coli, particularly under stress conditions . Mutants lacking MiaA exhibit pleiotropic phenotypes, including reduced growth rate and increased sensitivity to environmental stresses .

Biochemical Characterization

MiaA belongs to the family of tRNA isopentenyltransferases, which catalyze the transfer of a dimethylallyl group from dimethylallyl pyrophosphate (DMAPP) to tRNA . The Salmonella typhimurium MiaE protein, which is involved in tRNA modification, has been characterized as a monooxygenase that converts ms2i6A to ms2io6A at position 37 within the tRNA substrate .

Impact on Bacterial Pathogenesis and Symbiosis

The activity of MiaA is crucial for the pathogenesis of Photorhabdus luminescens and its symbiotic relationship with nematodes . Disruption of MiaA function can lead to:

• Reduced Production of Secondary Metabolites: The bacterium's ability to produce secondary metabolites, which are essential for nematode development and replication, is compromised .

• Impaired Insecticidal Activity: The symbiotic relationship between Photorhabdus luminescens and nematodes is critical for infecting and killing insect larvae; disruption of this symbiosis reduces insecticidal activity .