Mechanism of Na+/H+ antiporting

Na+/H+ antiporters are central to cellular salt and pH homeostasis. The structure of Escherichia coli NhaA was recently determined, but its mechanisms of transport and pH regulation remain elusive. We performed molecular dynamics simulations of NhaA that, with existing experimental data, enabled us to propose an atomically detailed model of antiporter function. Three conserved aspartates are key to our proposed mechanism: Asp164 (D164) is the Na+-binding site, D163 controls the alternating accessibility of this binding site to the cytoplasm or periplasm, and D133 is crucial for pH regulation. Consistent with experimental stoichiometry, two protons are required to transport a single Na+ ion: D163 protonates to reveal the Na+-binding site to the periplasm, and subsequent protonation of D164 releases Na+. Additional mutagenesis experiments further validated the model.     

DNA diagnostics--molecular techniques and automation

Molecular biology has revolutionized the understanding of many aspects of human disease. Ongoing developments in DNA diagnostics--the analysis of disease at the nucleic acid level--will soon provide automated, rapid, and inexpensive analyses for DNA or RNA sequences associated with genetic, malignant, and infectious diseases. DNA diagnostics will also facilitate the identification of disease-associated genes at birth, thus creating new opportunities for preventive medicine.