From microbial to lens βγ-crystallins: Presence of a universal calcium-binding motif in βγ-crystallin superfamily

Crystallins which form the major protein components of the eye lens are responsible for its transparency. βγ-crystallin superfamily has a well-characterized protein fold which is present in several members in prokaryotes and eukaryotes. Apart from two members from eukaryote, Spherulin 3a and Ciona crystallin, a majority of them possess the two or more βγ-crystallin domains. The βγ domain consists of two Greek key motifs arranged as four antiparallel β-strands. Since a very long time, calcium connection with lens crystallins has been a debatable issue. Here in this article, we summarize the recent advances about how this domain evolved from bacteria to chordates to perform specialized functions. Emphasis is put on summarizing the calcium-binding properties of the members from prokaryotes and eukaryotes, and the definition of a universal motif of calciumbinding in the proteins of this superfamily.