Can flavoprotein monooxygenases functionalize long-chain n-alkanes?

Area of Science:

• Biochemistry
• Enzymology
• Industrial Biotechnology

Background:

• Long-chain n-alkane functionalization is crucial for industrial and environmental applications but is challenging due to the stability of C-H bonds.
• Biocatalysis offers selective and eco-friendly alternatives, with enzymes like AlkB, LadA, and AlmA being investigated.
• LadA and AlmA are soluble, metal-free flavin-dependent enzymes, making them attractive targets for bioengineering.

Purpose of the Study:

• To reproduce and optimize the n-alkane monooxygenase activity of the flavoprotein LadA.
• To evaluate the activity of an optimized LadA variant and four novel homologs.
• To clarify the biochemical role of LadA and AlmA in long-chain n-alkane metabolism.

Main Methods:

• In vitro assays were performed to test the hydroxylation activity of LadA, its optimized variant, and four homologs.
• Protein superfamily analysis was conducted to understand LadA's potential functions.
• Literature review of experimental evidence for LadA and AlmA was performed.

Main Results:

• No detectable long-chain n-alkane hydroxylation activity was observed for LadA, its optimized variant, or the tested homologs under in vitro conditions.
• Analysis suggests LadA might be involved in long-chain alkane metabolism, but its role in initial oxo-functionalization remains unconfirmed.
• Previous studies on AlmA reported similar inconclusive results regarding its monooxygenase activity.

Conclusions:

• The findings challenge the established understanding of flavoprotein monooxygenases, specifically LadA and AlmA, as direct long-chain n-alkane monooxygenases.
• The precise biochemical role of these enzymes in alkane metabolism requires further investigation.
• This study highlights the need for continued research to elucidate the function of flavoproteins in alkane functionalization.