NMR was used to obtain spectroscopic evidence supporting a two domain model for zoocin A in which an N-terminal catalytic domain is linked by a threonine-proline rich linker to a target recognition domain responsible for recognizing the cell wall of bacteria susceptible to the bacteriolytic action of the enzyme. When cloned and separately expressed, each domain retains the folding found in the whole enzyme. Additionally, spectroscopy suggests that the target recognition domain has a conformation typical of a soluble globular protein, while the catalytic domain aggregates at low millimolar concentrations. (C) 2004 Elsevier Inc. All rights reserved.