The structures and building blocks of the native protein G B1 domain and the engineered protein. The sources used in engineering protein are also shown. Building block-I (BB-I) is shown in red and building blocks-II (BB-II) is highlighted in green. The unassigned and unused residues are in yellow. (A) The two building blocks of the native protein G B1 domain. Building block-I (BB-I, residues 2–36) consists of a β-hairpin and an α-helix. Building block-II (BB-II, residues 37–56) is a β-hairpin. (B) The two building blocks of the engineered protein (protein G-like; eng-2gb1). Similar to BB-I in nat-2gb1, BB-I of eng-2gb1 also consists of a β-hairpin and an α-helix, whereas BB-II is a β-hairpin. (C) The structure of the Protein L B1 Domain, the source protein used for the engineered protein. The fragment used for engineering eng-2gb1 is highlighted in red. (D) The structure of diisopropylfluorophosphatase, the source protein of BB-II in eng-2gb1. The fragment used in engineering eng-2gb1 is denoted in green.