H-capacitor and ATP production in obligate alkaliphilic : insights into cytochrome and H transport mechanisms.

Alkaliphilic strains likely utilize a limited number of free H, producing ATP through an H-based electrochemical membrane potential more efficiently than neutralophiles do. One possible mechanism responsible for this involves a structure that accumulates H through a hydrogen-bonding network formed by water molecules and the acidic, amido-, and hydroxyl- groups of amino acids located at the N-terminal site of membrane-bound cytochromes , which are specifically found in obligate alkaliphiles. The segment of cytochromes facilitates the formation of an H-capacitor at the outer membrane surface. The H-capacitor would produce an additional unbalanced vertical force to drive FF-ATP synthase via H concentrations and electrical charges across the membrane. Accumulated H ions are transferred from cytochrome to the H influx gate of the -subunit of FF-ATP synthase. However, the relative abundance of protonable basic amino acids at this site is low, suggesting that H transfer occurs via a membrane-bound protein containing the DUF2759 domain. This protein exposes basic amino acids that outnumber the deprotonatable acidic amino acids, effectively recruiting H from cytochrome near the H influx gate of FF-ATP synthase. The disparity in abundance between acidic and basic amino acids within the H carrier segment may play a crucial role in determining H transfer efficiency. In alkaliphiles, significant gaps in H release or acceptance exist between the outer membrane and the intracellular side of FF-ATP synthase. This indicates that the hydrophilic segments involved in H transfer are specifically designed to enhance the performance of FF-ATP synthase. This hypothetical mechanism for the effective transportation of accumulated H to the N-terminal region of the cytochrome amino acid sequence is essential for ATP production in obligate alkaliphilic . The unique bioenergetic configuration of these alkaliphiles is evident in their high maximum ATP production rates. Maximizing the activity of FF-ATP synthase can be achieved through efficient H transport and a high transmembrane electrical potential (ΔΨ), particularly in environments where H availability is limited.