title: Evolutionary remodeling of βγ-crystallins for domain stability at cost of Ca2+ binding.
abstract: The topologically similar βγ-crystallins that are prevalent in all kingdoms of life have evolved for high innate domain stability to perform their specialized functions. The evolution of stability and its control in βγ-crystallins that possess either a canonical (mostly from microorganisms) or degenerate (principally found in vertebrate homologues) Ca2+-binding motif is not known. Using equilibrium unfolding of βγ-crystallin domains (26 wild-type domains and their mutants) in apo- and holo-forms, we demonstrate the presence of a stability gradient across these members, which is attained by the choice of residues in the (N/D)(N/D)XX(S/T)S Ca2+-binding motif. The occurrence of a polar, hydrophobic, or Ser residue at the 1st, 3rd, or 5th position of the motif is likely linked to a higher domain stability. Partial conversion of a microbe-type domain (with a canonical Ca2+-binding motif) to a vertebrate-type domain (with a degenerate Ca2+-binding motif) by mutating serine to arginine/lysine disables the Ca2+-binding but significantly augments its stability. Conversely, stability is compromised when arginine (in a vertebrate-type disabled domain) is replaced by serine (as a microbe type). Our results suggest that such conversions were acquired as a strategy for desired stability in vertebrate members at the cost of Ca2+-binding. In a physiological context, we demonstrate that a mutation such as an arginine to serine (R77S) mutation in this motif of γ-crystallin (partial conversion to microbe-type), implicated in cataracts, decreases the domain stability. Thus, this motif acts as a "central tuning knob" for innate as well as Ca2+-induced gain in stability, incorporating a stability gradient across βγ-crystallin members critical for their specialized functions.
authors.affiliation: Centre for Cellular and Molecular Biology, Council of Scientific and Industrial Research, Uppal Road, Hyderabad-500007, India.
authors.forename: Shashi Kumar
authors.initials: SK
authors.lastname: Suman
authors.affiliation: Centre for Cellular and Molecular Biology, Council of Scientific and Industrial Research, Uppal Road, Hyderabad-500007, India.
authors.forename: Amita
authors.initials: A
authors.lastname: Mishra
authors.affiliation: Centre for Cellular and Molecular Biology, Council of Scientific and Industrial Research, Uppal Road, Hyderabad-500007, India.
authors.forename: Daddali
authors.initials: D
authors.lastname: Ravindra
authors.affiliation: Centre for Cellular and Molecular Biology, Council of Scientific and Industrial Research, Uppal Road, Hyderabad-500007, India.
authors.forename: Lahari
authors.initials: L
authors.lastname: Yeramala
authors.affiliation: Centre for Cellular and Molecular Biology, Council of Scientific and Industrial Research, Uppal Road, Hyderabad-500007, India. Electronic address: yogendra@ccmb.res.in.
authors.forename: Yogendra
authors.initials: Y
authors.lastname: Sharma
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001120:Arginine / Q000737:chemistry; D002118:Calcium / Q000737:chemistry*; D002417:Cattle; D003013:Clostridium / Q000378:metabolism; D005417:Flavobacterium / Q000378:metabolism; D017020:Methanosarcina / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D042182:Rhodospirillum centenum / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D012694:Serine / Q000737:chemistry; D013816:Thermodynamics; D014734:Vibrio cholerae / Q000378:metabolism; D038204:beta-Crystallins / Q000737:chemistry* / Q000235:genetics; D038222:gamma-Crystallins / Q000737:chemistry* / Q000235:genetics
chemical_list: D038204:beta-Crystallins; D038222:gamma-Crystallins; D012694:Serine; D001120:Arginine; D002118:Calcium