SecM facilitates translocase function of SecA by localizing its biosynthesis.

Area of Science:

• Molecular Biology
• Cell Biology
• Protein Biochemistry

Background:

• The SecM protein in Escherichia coli is known to arrest its own translation.
• This arrest mechanism is crucial for regulating the expression of SecA, a key protein export factor.
• The interaction of SecM with the ribosomal exit tunnel and its release upon cotranslational export are established processes.

Purpose of the Study:

• To investigate a previously unrecognized role of SecM in facilitating SecA activities.
• To determine how SecM's interaction with the translocon influences SecA functionality.
• To elucidate the impact of SecM's structural integrity and localization on SecA's functional conformation.

Main Methods:

• Systematic analysis of SecA-protein export relationships in Escherichia coli cells with varying SecA levels.
• Assessment of SecA functionality under conditions where SecM is absent, mutated, or lacks its signal sequence.
• Investigating the correlation between SecM's cotranslational targeting and SecA's functional state.

Main Results:

• SecA function was significantly impaired when SecM was absent upstream of the secM-secA message.
• Mutations in SecM's arrest sequence or the absence of its signal sequence also led to reduced SecA functionality.
• These findings indicate that the cotranslational targeting of nascent SecM to the translocon is vital for SecA's functional maturation.

Conclusions:

• SecM plays a critical, previously unappreciated role in promoting SecA functionality beyond regulating its expression.
• Cotranslational targeting of SecM to the membrane-associated translocon facilitates the proper folding and activation of SecA.
• This proximity-dependent mechanism ensures that the multiconformation ATPase SecA adopts a ready-to-function state.