Nutrient transport suggests an evolutionary basis for charged archaeal surface layer proteins

Area of Science:

• Microbiology
• Biophysics
• Biochemistry

Background:

• Surface layers (S-layers) are protein lattices forming the outer cell envelope of archaea and bacteria.
• S-layer proteins (SLPs) form nanoporous crystalline sheets and often contain charged amino acids.
• The function of S-layers and the role of charged SLPs in cellular metabolism remain largely unknown.

Purpose of the Study:

• To provide a rationale for charged S-layer proteins within the context of S-layer structural evolution.
• To investigate the influence of S-layer nanopores on solute diffusion and cellular metabolism.
• To elucidate the mechanism behind the ability of ammonia-oxidizing archaea (AOA) to thrive in low-ammonium environments.

Main Methods:

• Utilized ammonia-oxidizing archaea (AOA) as a model system for S-layer geometry.
• Employed a 2D electrodiffusion reaction computational framework to simulate solute diffusion and consumption.
• Modeled the diffusion and consumption of the charged solute ammonium (NH4+).

Main Results:

• Nanoporous S-layers significantly elevate the concentration of NH4+ in the pseudo-periplasmic space.
• The characteristic length scales of S-layers play a crucial role in this concentration effect.
• Simulations revealed that charged SLPs can enhance NH4+ availability for AOA.

Conclusions:

• The study suggests an evolutionary and mechanistic basis for the charge of S-layer proteins.
• Charged S-layers facilitate ammonia oxidation in AOA by concentrating nanomolar NH4+.
• Findings have broad implications for understanding ecologically distinct microbial populations and their metabolic strategies.