title: Ca2+ and βγ-crystallins: An affair that did not last?
abstract: BACKGROUND
  During the last three decades, lens β- and γ-crystallins have found a huge number of kin from numerous taxonomical sources. Most of these proteins from invertebrates and microbes have been demonstrated or predicted to bind Ca2+ involving a distinct double-clamp motif, which is largely degenerated in lens homologues.
  
  
  METHODS
  The various aspects of transformation of βγ-crystallins from a quintessential Ca2+-binding protein into a primarily structural molecule have been reviewed.
  
  
  CONCLUSIONS
  In lens members of βγ-crystallins, the residues involved in Ca2+ binding have diverged considerably from the classical consensus with consequent reduction in their Ca2+-binding properties. This evolutionary change is congenial to their new role as robust constituents of lens. The exact functions of the residual affinity for Ca2+ are yet to be established.
  
  
  CONCLUSIONS
  This review highlights the significance of reduction in Ca2+-binding ability of the βγ-crystallins for lens physiology and why this residual affinity may be functionally important. This article is part of a Special Issue entitled Crystallin Biochemistry in Health and Disease.
authors.affiliation: CSIR-Centre for Cellular and Molecular Biology (CCMB), Uppal Road, Hyderabad 500 007, India.
authors.forename: Amita
authors.initials: A
authors.lastname: Mishra
authors.affiliation: CSIR-Centre for Cellular and Molecular Biology (CCMB), Uppal Road, Hyderabad 500 007, India.
authors.forename: Bal
authors.initials: B
authors.lastname: Krishnan
authors.affiliation: CSIR-Centre for Cellular and Molecular Biology (CCMB), Uppal Road, Hyderabad 500 007, India.
authors.forename: Rajeev
authors.initials: R
authors.lastname: Raman
authors.affiliation: CSIR-Centre for Cellular and Molecular Biology (CCMB), Uppal Road, Hyderabad 500 007, India. Electronic address: yogendra@ccmb.res.in.
authors.forename: Yogendra
authors.initials: Y
authors.lastname: Sharma
mesh_terms: D000818:Animals; D001665:Binding Sites / Q000235:genetics; D002118:Calcium / Q000378:metabolism*; D019143:Evolution, Molecular; D005136:Eye Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007908:Lens, Crystalline / Q000378:metabolism*; D008957:Models, Genetic; D011485:Protein Binding / Q000235:genetics; D038204:beta-Crystallins / Q000502:physiology*; D038222:gamma-Crystallins / Q000502:physiology*
chemical_list: D005136:Eye Proteins; D038204:beta-Crystallins; D038222:gamma-Crystallins; D002118:Calcium
keywords: Ca(2+)-binding; Lens; Lens transparency; β- and γ-crystallins; βγ-Crystallin domain