ApaH decaps Np₄N-capped RNAs in two alternative orientations.

Area of Science:

• Molecular Biology
• Enzymology
• Structural Biology

Background:

• Dinucleoside tetraphosphates (Np4Ns), or alarmones, function as precursors for Np4 caps on bacterial transcripts.
• These caps influence RNA longevity and bacterial adaptation to stress.
• ApaH is the primary enzyme in proteobacteria responsible for hydrolyzing Np4Ns and removing Np4 caps from RNA.

Purpose of the Study:

• To elucidate the catalytic mechanism of Escherichia coli ApaH, a symmetric Np4N hydrolase.
• To investigate the enzyme's interaction with various Np4Ns and Np4-capped RNAs.
• To understand the implications of substrate recognition for enzyme activity and drug design.

Main Methods:

• Biochemical assays to study enzyme kinetics and substrate hydrolysis.
• Structural studies to determine the enzyme-substrate complex.
• Analysis of ApaH's interaction with different Np4Ns and Np4-capped mRNAs and sRNAs.

Main Results:

• Escherichia coli ApaH exhibits a unique substrate recognition mechanism, accommodating substrates in two orientations with a slight preference.
• The enzyme efficiently decaps various Np4-capped messenger RNAs (mRNAs) and small RNAs (sRNAs).
• ApaH's activity significantly impacts the lifetimes of Np4-capped RNAs.

Conclusions:

• ApaH's dual substrate orientation recognition is key to its broad substrate specificity.
• The enzyme's decapping activity plays a crucial role in regulating RNA turnover in bacteria.
• Understanding substrate orientation is vital for designing effective enzyme-inhibiting drugs, as alternative orientations may evade inhibition.