Molecular basis for ATPase-powered substrate translocation by the Lon AAA+ protease

Area of Science:

• Molecular Biology
• Structural Biology
• Biochemistry

Background:

• The Lon AAA+ protease (LonA) is a crucial enzyme that utilizes ATP hydrolysis to power protein degradation.
• Understanding the mechanical forces and conformational changes LonA employs for substrate translocation is key to elucidating its function.

Purpose of the Study:

• To determine the structural basis of substrate translocation in LonA.
• To visualize the mechanism by which LonA engages and translocates substrates into its proteolytic chamber.

Main Methods:

• Cryo-electron microscopy (cryo-EM) was used to determine the structure of Meiothermus taiwanensis LonA (MtaLonA).
• The structure was resolved at 3.6 Å resolution in a substrate-engaged state.

Main Results:

• The cryo-EM structure revealed substrate interactions mediated by dual pore loops within the ATPase domains.
• A spiral staircase arrangement of four protomers in distinct nucleotide-bound states (ATP/ADP) was observed.
• A closed AAA+ ring is maintained by two ADP-bound protomers, facilitating a rotary translocation mechanism.

Conclusions:

• LonA employs a processive rotary translocation mechanism.
• Substrate binding induces LonA-specific, nucleotide-dependent allosteric coordination among its ATPase domains.
• This mechanism is essential for driving substrate movement into the proteolytic chamber.