Dihydrodipicolinate synthase (DHDPS) is an oligomeric enzyme that catalyses the rate-limiting and first committed step in the lysine biosynthesis pathway of bacteria and plants. In plants and Gram-negative bacteria, DHDPS is allosterically inhibited by lysine, the downstream product of the pathway. However, plant DHDPS enzymes demonstrate significantly tighter allosteric inhibition by lysine than their bacterial counterparts. To accommodate the allosteric site for binding lysine, DHDPS needs to form a dimeric structure. However, there have been three different quaternary architectures reported for DHDPS, namely (i) ‘head-to-head’ tetrameric forms common to most eubacterial species, (ii) tight dimers observed in some bacterial species including S. aureus, and (iii) ‘back-to-back’ tetrameric forms canonical to plant species. Hitherto, DHDPS has not yet been characterised from cyanobacteria, which are recognised as the closest prokaryotic evolutionary ancestors to plants. We therefore hypothesise that DHDPS from the cyanobacterial species, Prochlorococcus marinus (Pm) will adopt quaternary structure and allosteric regulatory features that are canonical to plant DHDPS enzymes, namely (i) formation of ‘back-to-back’ homotetramers and (ii) tight allosteric inhibition by lysine. We have thus cloned, expressed and purified Pm-DHDPS, and are currently characterising the quaternary structure and enzyme kinetic properties of the recombinant enzyme in solution using an array of biophysical techniques. This project will offer insight into the molecular evolution in quaternary structure and allosteric regulation of an important bacterial and plant enzyme.