We recently demonstrated that the conger eel galectins, Congerin I and II, have evolved under significant selective pressure, with the emergence of a new strand-swap structure between subunits in Congerin I. To understand the structure-thermostability relationship of Congerins, and seek clues to the mechanism of their evolution, we improved the thermostability of Congerin II by rational design and in vitro evolutionary protein engineering. A resulting Tyr16/Thr88 double mutant exhibited structural features and thermostability similar to the naturally thermostable isoform, Congerin I. Thus, ...