prl mutations in the Escherichia coli secG gene

Area of Science:

• Microbiology
• Molecular Biology
• Protein Transport

Background:

• SecG is an integral membrane protein essential for the efficiency of the Escherichia coli preprotein translocase.
• SecG function involves cycles of topology inversion, coupled with SecA insertion-deinsertion cycles.
• Previous studies identified sec alleles of secG causing secretion defects.

Purpose of the Study:

• To identify novel functions of SecG in protein export.
• To investigate the role of SecG in signal sequence recognition and membrane protein topology.

Main Methods:

• Screening of mutagenized secG libraries.
• Selection of prl alleles of secG as suppressors of a malE signal sequence mutation.
• Analysis of prlH suppressor mutations and their effects on protein export.

Main Results:

• Isolated prl alleles of secG, termed prlH mutations, affecting distinct codons from known sec mutations.
• Demonstrated that prlH suppressors can correct various signal sequence mutations and facilitate export of proteins lacking signal sequences.
• Showed that some prlH alleles are as potent as strong prlG alleles of SecE.
• Observed that prlH alleles can promote export of alkaline phosphatase fused to predicted cytoplasmic domains of UhpT.

Conclusions:

• SecG plays a significant role in signal sequence recognition.
• SecG may also be involved in determining the topology of integral membrane proteins.
• The findings expand the understanding of the preprotein translocase machinery and SecG's multifaceted role.