This domain is found at the C-terminal domain of the insulin-like growth factor II (IGF-2, also see Pfam:PF00049) in vertebrates and seems to represent the E-peptide [1,2].

1: Insulin-like growth factors. LeRoith D, Roberts CT Jr; Ann N Y Acad Sci 1993;692:1-9. PMID:8215015

2: Antibodies directed against the E region of pro-insulin-like growth factor-II used to evaluate non-islet cell tumor-induced hypoglycemia. van Doorn J, Hoogerbrugge CM, Koster JG, Bloemen RJ, Hoekman K, Mudde AH, van Buul-Offers SC; Clin Chem 2002;48:1739-1750. PMID:12324491