This disclosure features fusion proteins comprising a base protein linked to or incorporated in a CH2 scaffold of IgG. The CH2 scaffold can derive from the macaque CH2 domain of IgG. The fusion proteins can effectively bind a single or multiple targets, and can be engineered to regulate effector functions as desired. The fusion proteins can have an increased serum half-life, solubility, stability, protease resistance, and/or expression as compared to the scaffolds alone and/or as compared to the base protein alone. This disclosure also features fusion proteins comprising a base protein, a CH2 scaffold and a discrete polyethylene glycol (dPEG) linked to the scaffold via a serine, tyrosine, cysteine, lysine, or a glycosylation site of the scaffold. This disclosure additionally features scaffolds linked to a discrete polyethylene glycol (dPEG) via a serine, tyrosine, cysteine, or lysine of the scaffolds or a glycosylation site of the scaffold.
