Involved in the biosynthesis of carbapenam-3-carboxylate, a beta-lactam antibiotic of the carbapenem class. Catalyzes the ATP-dependent formation of (3S,5S)-carbapenam-3-carboxylate from (2S,5S)-5-carboxymethylproline. (2S,5S)-5-carboxymethylproline + ATP = (3S,5S)-carbapenam-3-caboxylate + AMP + diphosphate + H(+) kcat is 0.28 sec(-1). Optimum pH is 8.5. Antibiotic biosynthesis; carbapenem biosynthesis. Homotetramer.