Multiple signals direct the assembly and function of a type 1 secretion system.

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Type 1 secretion systems (T1SS) are crucial protein transport pathways in Gram-negative bacteria.
• T1SS mediate the secretion of diverse substrates, including proteases, lipases, and hemophores.
• These systems comprise an inner membrane ABC protein, a periplasmic adaptor, and an outer membrane TolC channel.

Purpose of the Study:

• To investigate the non-C-terminal regions of the hemophore HasA involved in T1SS-mediated secretion.
• To elucidate the mechanism by which HasA interacts with the T1SS ABC protein (HasD).
• To understand how substrate interaction with T1SS regulates complex assembly and disassembly.

Main Methods:

• Site-directed mutagenesis of the HasA protein.
• Bacterial secretion assays.
• Analysis of protein-substrate interactions and T1SS complex assembly/disassembly.

Main Results:

• Identified numerous, distributed, linear regions in HasA, in addition to the C-terminal signal, that are essential for efficient secretion.
• Demonstrated that these regions, along with the C-terminal signal, stabilize the T1SS complex during secretion.
• Showed that the C-terminal signal of HasA triggers ATP hydrolysis by the ABC protein (HasD), leading to complex disassembly.

Conclusions:

• T1SS secretion involves a multistep interaction between the substrate and the ABC protein, stabilizing the secretion machinery.
• The C-terminal signal acts as a trigger for complex disassembly after substrate presentation.
• This mechanism ensures tight coupling between protein synthesis and secretion in bacteria.