  Most known proteins in nature consist of multiple domains. Interactions
between domains may lead to unexpected folding and misfolding phenomena. This
study of human {\gamma}D-crystallin, a two-domain protein in the eye lens,
revealed one such surprise: conformational catalysis of misfolding via
intermolecular domain interface ''stealing''. An intermolecular interface
between the more stable domains outcompetes the native intramolecular domain
interface. Loss of the native interface in turn promotes misfolding and
subsequent aggregation, especially in cataract-related {\gamma}D-crystallin
variants. This phenomenon is likely a contributing factor in the development of
cataract disease, the leading worldwide cause of blindness. However, interface
stealing likely occurs in many proteins composed of two or more interacting
domains.
