Journal Article

Hydroimidazolone Modification of the Conserved Arg12 in Small Heat Shock Proteins: Studies on the Structure and Chaperone Function Using Mutant Mimics

Panda, Alok Kumar, Santhoshkumar, Puttur, Shanthakumar, Shilpa, Nagaraj, Ram H., Wang, Benlian, Pasupuleti, NagaRekha, Biswas, Ashis

2012

Overview

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.

• Publisher: Public Library of Science,Public Library of Science (PLoS)
• Subject: Adducts / Age / Aging / Alanine / alpha-Crystallin A Chain - chemistry / alpha-Crystallin A Chain - genetics / alpha-Crystallin A Chain - metabolism / alpha-Crystallin B Chain - chemistry / alpha-Crystallin B Chain - genetics / alpha-Crystallin B Chain - metabolism / Alzheimer's disease / Amino Acid Sequence / Amino acids / Arginine / Arginine - chemistry / Arginine - genetics / Arginine - metabolism / Binding sites / Binding Sites - genetics / Biochemistry / Biology / Biopolymers / Cataracts / Circular Dichroism / Crystal structure / Crystallin / Crystallinity / Electrophoresis, Polyacrylamide Gel / Heat shock proteins / HSP27 Heat-Shock Proteins - chemistry / HSP27 Heat-Shock Proteins - genetics / HSP27 Heat-Shock Proteins - metabolism / Hsp27 protein / Imidazoles - chemistry / Imidazoles - metabolism / Kinetics / Medicine / Molecular Chaperones - chemistry / Molecular Chaperones - genetics / Molecular Chaperones - metabolism / Molecular Sequence Data / Molecular Structure / Mutation / Physiological aspects / Protein binding / Protein Binding - drug effects / Protein interaction / Protein structure / Protein Structure, Secondary - drug effects / Protein Structure, Tertiary - drug effects / Proteins / Pyruvaldehyde / Pyruvaldehyde - pharmacology / Recombinant Proteins - chemistry / Recombinant Proteins - metabolism / Residues / Sequence Homology, Amino Acid / Small heat shock proteins / Spectrometry, Fluorescence / Structural stability / Structure-function relationships / Tertiary structure / Thermodynamics