Catalyzes the attachment of proline to tRNA(Pro) in a two-step reaction: proline is first activated by ATP to form Pro-AMP and then transferred to the acceptor end of tRNA(Pro). Can inadvertently accommodate and process cysteine. ATP + L-proline + tRNA(Pro) = AMP + diphosphate + L-prolyl-tRNA(Pro) Homodimer. The dimer is functionally asymmetric: only one of the two active sites at a time is able to form prolyl-adenylate, and only one tRNA molecule binds per dimer. Interacts with LeuRS, which enhances tRNA(Pro) aminoacylation. Consists of three domains: the N-terminal catalytic domain, the anticodon-binding domain and the C-terminal extension. The C-terminal extension binds a zinc ion, which probably plays a non-essential structural role in stabilizing the fold of C-terminal domain. Belongs to the class-II aminoacyl-tRNA synthetase family. ProS type 3 subfamily.