This family of proteins are likely to act as amidoligase enzymes [1] Protein in this family are found in conserved gene neighborhoods encoding a glutamine amidotransferase-like thiol peptidase (in proteobacteria) or an Aig2 family cyclotransferase protein (in firmicutes) [1].

1: Unraveling the biochemistry and provenance of pupylation: a prokaryotic analog of ubiquitination. Iyer LM, Burroughs AM, Aravind L; Biol Direct. 2008;3:45. PMID:18980670