Preferential attachment in the evolution of metabolic networks

Area of Science:

• Systems biology
• Network science
• Biochemistry

Background:

• Biological networks often display scale-free properties.
• Scale-free networks can grow via preferential attachment, favoring connections to highly connected nodes.
• This implies older nodes typically possess higher average connectivity than newer ones.

Purpose of the Study:

• Investigate preferential attachment within the metabolic network of Escherichia coli.
• Determine if metabolic network evolution follows principles seen in other scale-free networks.

Main Methods:

• Analyzed enzyme connectivities in the E. coli metabolic network.
• Compared connectivity of E. coli enzymes with their representatives across diverse species (eukaryotes, bacteria, archaea).
• Examined enzyme connectivity in relation to horizontal gene transfer candidates.

Main Results:

• E. coli enzymes with eukaryotic representatives showed higher average connectivity.
• Enzymes unique to prokaryotes, particularly betagamma-proteobacteria, had lower-than-expected connectivity.
• Enzymes suspected of horizontal gene transfer exhibited significantly higher average connectivity.
• New connections preferentially formed with highly connected enzymes, supporting preferential attachment.

Conclusions:

• Evidence suggests preferential attachment in the E. coli metabolic network.
• Preferential growth may stem from gene duplication, where novel enzymes retain ancestral compound involvement.
• High connectivity of horizontal gene transfer candidates indicates their integration into the network's core.
• E. coli likely adapts its metabolic network by incorporating central enzymes via horizontal gene transfer for environmental suitability.