Energy Transduction and Protein Interactions at Extreme pH

Studies of organisms that grow under extreme conditions provide important information about the evolution of metabolic mechanisms and structure-function relationships in proteins under extreme conditions. Through a research program with collaborators at the Centre Nationale de la Recherche Scientifique, Marseille, we are endeavoring to characterize mechanisms of energy transduction in the extremophile, Thiobacillus ferrooxidans. This obligate autotroph derives most of its energy from the oxidation of ferrous iron to ferric iron and grows optimally at pH 2 and, consequently, is employed by the mining energy to extract low levels of commercially important elements (uranium, gold, copper) from the slag heaps of primary mining operations.

Bonnefoy and her colleagues at the CNRS have developed a procedure for mobilizing genetic elements from this extremophile into E. coli where protein products can obtained and purified at normal pH's. Furthermore, they have identified an operon which encodes a putative pathway of ferrous iron oxidation which includes a set of outer membrane and periplasmic cytochomes c, a periplasmic copper protein and a cytochrome oxidase presumed to be located on the inner membrane. We are currently producing these components from cloned genes expressed in E. coli in an attempt to reconstitute the pathway and characterize the interactions between components and the mechanisms of the transfer of electrons from ferrous iron outside the cell (at pH 2), through the periplasm (at pH 3) to the cytochrome oxidase and oxygen. We believe the study of the structures and interactions of these components at extreme acidic pH's will provide not only important general ideas concerning protein structure, function and interactions but also some concepts about what molecular evolutionary changes have occurred which permits survival and function under extreme conditions.