BACTERIAL ANION-EXCHANGE - REDUCTIONIST AND INTEGRATIVE APPROACHES TOMEMBRANE BIOLOGY

Studies of two different bacterial anion exchange proteins (antiporter s) led us to conclude that both reductionist and integrative approache s contribute to progress in understanding membrane biology. We have us ed a reductionist perspective in applying cysteine scanning mutagenesi s to probe individual amino acid positions of UhpT (uptake of hexose p hosphate transporter), the carrier responsible for transport of glucos e 6-phosphate by Escherichia coli. This work has established experimen tal criteria that should allow one to identify and localize the transl ocation pathway in such membrane proteins. An integrative view is exem plified by work with OxlT (oxalate transporter), the carrier used by a n anaerobe Oxalobacter formigenes to catalyze the antiport of divalent oxalate and monovalent formate. The activity of OxlT is functionally coordinated with that of a cytosolic oxalyl decarboxylase; together, t hese vectorial and scalar activities constitute a metabolic proton pum p, allowing O. formigenes to display decarboxylative phosphorylation. The role played by OxlT argues that membrane carriers can assume unant icipated emergent properties when their biochemical functions are prop erly articulated in relation to other aspects of cell function.