title: Gamma crystallins of the human eye lens.
abstract: BACKGROUND
  Protein crystallins co me in three types (α, β and γ) and are found predominantly in the eye, and particularly in the lens, where they are packed into a compact, plastic, elastic, and transparent globule of proper refractive power range that aids in focusing incoming light on to the retina. Of these, the γ-crystallins are found largely in the nuclear region of the lens at very high concentrations (>400 mg/ml). The connection between their structure and inter-molecular interactions and lens transparency is an issue of particular interest.
  
  
  METHODS
  We review the origin and phylogeny of the gamma crystallins, their special structure involving the use of Greek key supersecondary structural motif, and how they aid in offering the appropriate refractive index gradient, intermolecular short range attractive interactions (aiding in packing them into a transparent ball), the role that several of the constituent amino acid residues play in this process, the thermodynamic and kinetic stability and how even single point mutations can upset this delicate balance and lead to intermolecular aggregation, forming light-scattering particles which compromise transparency. We cite several examples of this, and illustrate this by cloning, expressing, isolating and comparing the properties of the mutant protein S39C of human γS-crystallin (associated with congenital cataract-microcornea), with those of the wild type molecule. In addition, we note that human γ-crystallins are also present in other parts of the eye (e.g., retina), where their functions are yet to be understood.
  
  
  CONCLUSIONS
  There are several 'crucial' residues in and around the Greek key motifs which are essential to maintain the compact architecture of the crystallin molecules. We find that a mutation that replaces even one of these residues can lead to reduction in solubility, formation of light-scattering particles and loss of transparency in the molecular assembly.
  
  
  CONCLUSIONS
  Such a molecular understanding of the process helps us construct the continuum of genotype-molecular structural phenotype-clinical (pathological) phenotype. This article is part of a Special Issue entitled Crystallin Biochemistry in Health and Disease.
authors.affiliation: Ophthalmic Molecular Genetics Section, National Eye Institute, Building 5635FL, Room 1S24, 5625 Fishers Lane, Rockville, MD 20852, United States. Electronic address: pullaraovv@gmail.com.
authors.forename: Venkata Pulla Rao
authors.initials: VP
authors.lastname: Vendra
authors.affiliation: Prof. Brien Holden Eye Research Centre, Hyderabad Eye Research Foundation, L. V. Prasad Eye Institute, Hyderabad 500034 Telangana, India. Electronic address: ismailkhan.hcu@gmail.com.
authors.forename: Ismail
authors.initials: I
authors.lastname: Khan
authors.affiliation: Plot 32, LIC Colony, W Marredpally, Secunderabad 500026, Telangana, India. Electronic address: sushilchandani@gmail.com.
authors.forename: Sushil
authors.initials: S
authors.lastname: Chandani
authors.affiliation: Department of Animal Science, Bharathidasan University, Tiruchirappalli 620 024, Tamil Nadu, India. Electronic address: anbu.blessings@gmail.com.
authors.forename: Anbukkarasi
authors.initials: A
authors.lastname: Muniyandi
authors.affiliation: Prof. Brien Holden Eye Research Centre, Hyderabad Eye Research Foundation, L. V. Prasad Eye Institute, Hyderabad 500034 Telangana, India. Electronic address: dbala@lvpei.org.
authors.forename: Dorairajan
authors.initials: D
authors.lastname: Balasubramanian
mesh_terms: D000595:Amino Acid Sequence; D005136:Eye Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007908:Lens, Crystalline / Q000737:chemistry* / Q000378:metabolism* / Q000473:pathology; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D013329:Structure-Activity Relationship; D038222:gamma-Crystallins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D005136:Eye Proteins; D038222:gamma-Crystallins
keywords: Cataractogenic mutations; Congenital cataract; Greek key motif; Human gamma crystallins; Structure–function correlation