title: Hydroimidazolone modification of the conserved Arg12 in small heat shock proteins: studies on the structure and chaperone function using mutant mimics.
abstract: Methylglyoxal (MGO) is an α-dicarbonyl compound present ubiquitously in the human body. MGO reacts with arginine residues in proteins and forms adducts such as hydroimidazolone and argpyrimidine in vivo. Previously, we showed that MGO-mediated modification of αA-crystallin increased its chaperone function. We identified MGO-modified arginine residues in αA-crystallin and found that replacing such arginine residues with alanine residues mimicked the effects of MGO on the chaperone function. Arginine 12 (R12) is a conserved amino acid residue in Hsp27 as well as αA- and αB-crystallin. When treated with MGO at or near physiological concentrations (2-10 µM), R12 was modified to hydroimidazolone in all three small heat shock proteins. In this study, we determined the effect of arginine substitution with alanine at position 12 (R12A to mimic MGO modification) on the structure and chaperone function of these proteins. Among the three proteins, the R12A mutation improved the chaperone function of only αA-crystallin. This enhancement in the chaperone function was accompanied by subtle changes in the tertiary structure, which increased the thermodynamic stability of αA-crystallin. This mutation induced the exposure of additional client protein binding sites on αA-crystallin. Altogether, our data suggest that MGO-modification of the conserved R12 in αA-crystallin to hydroimidazolone may play an important role in reducing protein aggregation in the lens during aging and cataract formation.
authors.affiliation: Department of Ophthalmology and Visual Sciences, Case Western Reserve University, Cleveland, Ohio, United States of America. ram.nagaraj@case.edu
authors.forename: Ram H
authors.initials: RH
authors.lastname: Nagaraj
authors.forename: Alok Kumar
authors.initials: AK
authors.lastname: Panda
authors.forename: Shilpa
authors.initials: S
authors.lastname: Shanthakumar
authors.forename: Puttur
authors.initials: P
authors.lastname: Santhoshkumar
authors.forename: NagaRekha
authors.initials: N
authors.lastname: Pasupuleti
authors.forename: Benlian
authors.initials: B
authors.lastname: Wang
authors.forename: Ashis
authors.initials: A
authors.lastname: Biswas
mesh_terms: D000595:Amino Acid Sequence; D001120:Arginine / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites / Q000235:genetics; D002942:Circular Dichroism; D004591:Electrophoresis, Polyacrylamide Gel; D055551:HSP27 Heat-Shock Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D007093:Imidazoles / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D018832:Molecular Chaperones / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009154:Mutation; D011485:Protein Binding / Q000187:drug effects; D017433:Protein Structure, Secondary / Q000187:drug effects; D017434:Protein Structure, Tertiary / Q000187:drug effects; D011765:Pyruvaldehyde / Q000494:pharmacology; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013050:Spectrometry, Fluorescence; D013816:Thermodynamics; D038202:alpha-Crystallin A Chain / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D038203:alpha-Crystallin B Chain / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D055551:HSP27 Heat-Shock Proteins; D007093:Imidazoles; D018832:Molecular Chaperones; D011994:Recombinant Proteins; D038202:alpha-Crystallin A Chain; D038203:alpha-Crystallin B Chain; C117197:imidazolone; D011765:Pyruvaldehyde; D001120:Arginine