Early Evolutionary Selection of NAD Biosynthesis Pathway in Bacteria

Area of Science:

• Biochemistry
• Microbiology
• Systems Biology

Background:

• Bacteria synthesize nicotinamide adenine dinucleotide (NAD) via two distinct pathways from nicotinamide (Nam).
• A short, two-step pathway involves nicotinamide mononucleotide (NMN) formation.
• A longer, four-step pathway includes deamidation and reamidation steps, appearing energetically unfavorable due to ATP cleavage.

Purpose of the Study:

• To investigate the energetic and stability trade-offs between the two NAD synthesis pathways in bacteria.
• To understand the prevalence of the seemingly less efficient pathway in bacteria, yeast, and plants.
• To determine if organisms select one pathway exclusively or utilize both.

Main Methods:

• Comparative analysis of chemical stability of pathway intermediates.
• Bioinformatic analysis of over 6000 bacterial genomes to assess pathway prevalence.
• Mathematical modeling of NAD pathway dynamics.

Main Results:

• The chemical stability of deamidated intermediates in the longer pathway can compensate for increased energy expenditure, particularly at elevated temperatures.
• Bioinformatic analyses reveal that bacteria predominantly utilize one pathway, indicating an early evolutionary selection.
• Mathematical modeling supports the hypothesis that possessing both pathways offers no significant advantage.

Conclusions:

• The prevalence of the longer NAD synthesis pathway is likely due to the enhanced chemical stability of its intermediates, balancing the energetic cost.
• Evolutionary selection favored the exclusive use of one pathway over the other in bacteria.
• Understanding these metabolic strategies provides insights into microbial biochemistry and evolution.