Radical SAM Enzymes Involved in Tetrapyrrole Biosynthesis and Insertion

Area of Science:

• Biochemistry
• Enzymology
• Microbiology

Background:

• Radical SAM enzymes are essential catalysts in anaerobic biosynthesis pathways for vital molecules like heme and bacteriochlorophyll.
• Several radical SAM enzymes, including CgdH, HemW, AhbC, AhbD, NirJ, and BchE, play distinct roles in tetrapyrrole metabolism across different microbial domains.

Purpose of the Study:

• To review the roles and mechanisms of radical SAM enzymes in anaerobic tetrapyrrole biosynthesis.
• To highlight the structural and functional diversity of these enzymes in heme and bacteriochlorophyll production.

Main Methods:

• Literature review and analysis of published studies on radical SAM enzymes in tetrapyrrole biosynthesis.
• Examination of solved crystal structures and biochemical characterizations of key enzymes.

Main Results:

• Coproporphyrinogen III dehydrogenase (CgdH) and BchE are examples of radical SAM enzymes with characterized structures and functions in heme and bacteriochlorophyll synthesis, respectively.
• Enzymes like AhbC, AhbD, and NirJ are involved in alternative heme biosynthesis routes, demonstrating pathway variations.

Conclusions:

• Radical SAM enzymes are indispensable for anaerobic tetrapyrrole biosynthesis, exhibiting diverse substrate specificities and catalytic mechanisms.
• Further research, particularly overcoming challenges in enzyme-substrate cocrystallization, is needed to fully elucidate the mechanisms of these enzymes.