This is the N-terminal domain found in ORF 2 (open reading frame 2), a protein encoded just downstream of asp (A. sobria serine protease). The ORF 2 N-terminal domain is essential for proper ASP folding. This domain is intrinsically disordered but forms some degree of secondary structure upon binding ASP [1, 2].

1: Structural Basis for Action of the External Chaperone for a Propeptide-deficient Serine Protease from Aeromonas sobria. Kobayashi H, Yoshida T, Miyakawa T, Tashiro M, Okamoto K, Yamanaka H, Tanokura M, Tsuge H; J Biol Chem. 2015;290:11130-11143. PMID:25784551

2: Involvement of the Arg566 residue of Aeromonas sobria serine protease in substrate specificity. Kobayashi H, Otsubo T, Teraoka F, Ikeda K, Seike S, Takahashi E, Okamoto K, Yoshida T, Tsuge H, Yamanaka H; PLoS One. 2017;12:e0186392. PMID:29023605