Escherichia coli represents one of the most widely used hosts for recombinant protein production, but its limited capacity for producing extracellular proteins is often cited as a drawback. NJ7G_0991 is an extracellular protein of the haloarchaeon Natrinema sp. J7-2 and comprises a signal peptide, a putative LolA-like domain, and a C-terminal domain of unknown function. Here, we found that the full-length (0991) and the C-terminal domain-deletion variant (0991 Delta C) of NJ7G_0991, but not its signal peptide-deletion variant (0991 Delta S), were efficiently released into the culture supernatant of E. coli without extensive cell lysis as determined by beta-galactosidase activity assay. After lysozyme treatment, E. coli cells producing 0991 or 0991 Delta C, but not 0991 Delta S, were converted from rod-shaped forms to spheres, suggesting that the secretion of 0991 or 0991 Delta C into the periplasm leads to an increase of outer membrane permeability of E. coli. A pelB signal peptide was fused to the N-terminus of the LolA-like domain, and the resulting variant PelB-0991 Delta C could be released into the culture supernatant of E. coli more efficiently than 0991 Delta C. By using PelB-0991 Delta C as a co-expression partner, the extracellular production level of a recombinant thermostable subtilase WF146 could be enhanced by up to 14-fold, and the extracellular concentration of an active site variant of WF146 (WF146-SA) reached up to 129 mg/l. To the best of our knowledge, this is the first report on archaeal protein-based co-expression system for extracellular production of recombinant proteins in E. coli.