title: Acetylation of αA-crystallin in the human lens: effects on structure and chaperone function.
abstract: α-Crystallin is a major protein in the human lens that is perceived to help to maintain the transparency of the lens through its chaperone function. In this study, we demonstrate that many lens proteins including αA-crystallin are acetylated in vivo. We found that K70 and K99 in αA-crystallin and, K92 and K166 in αB-crystallin are acetylated in the human lens. To determine the effect of acetylation on the chaperone function and structural changes, αA-crystallin was acetylated using acetic anhydride. The resulting protein showed strong immunoreactivity against a N(ε)-acetyllysine antibody, which was directly related to the degree of acetylation. When compared to the unmodified protein, the chaperone function of the in vitro acetylated αA-crystallin was higher against three of the four different client proteins tested. Because a lysine (residue 70; K70) in αA-crystallin is acetylated in vivo, we generated a protein with an acetylation mimic, replacing Lys70 with glutamine (K70Q). The K70Q mutant protein showed increased chaperone function against three client proteins compared to the Wt protein but decreased chaperone function against γ-crystallin. The acetylated protein displayed higher surface hydrophobicity and tryptophan fluorescence, had altered secondary and tertiary structures and displayed decreased thermodynamic stability. Together, our data suggest that acetylation of αA-crystallin occurs in the human lens and that it affects the chaperone function of the protein.
authors: Department of Ophthalmology and Visual Sciences, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA. ram.nagaraj@case.edu
authors: Ram H
authors: RH
authors: Nagaraj
authors: Rooban B
authors: RB
authors: Nahomi
authors: Shilpa
authors: S
authors: Shanthakumar
authors: Mikhail
authors: M
authors: Linetsky
authors: Smitha
authors: S
authors: Padmanabha
authors: Nagarekha
authors: N
authors: Pasupuleti
authors: Benlian
authors: B
authors: Wang
authors: Puttur
authors: P
authors: Santhoshkumar
authors: Alok Kumar
authors: AK
authors: Panda
authors: Ashis
authors: A
authors: Biswas
mesh_terms: D000089:Acetic Anhydrides / Q000378:metabolism; D000107:Acetylation; D003459:Crystallins; D005973:Glutamine / Q000378:metabolism; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D007908:Lens, Crystalline / Q000737:chemistry* / Q000378:metabolism*; D008239:Lysine / Q000378:metabolism; D008875:Middle Aged; D018832:Molecular Chaperones / Q000737:chemistry* / Q000378:metabolism*; D050505:Mutant Proteins / Q000737:chemistry / Q000378:metabolism; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D013050:Spectrometry, Fluorescence / Q000379:methods; D013329:Structure-Activity Relationship; D013816:Thermodynamics; D014364:Tryptophan / Q000378:metabolism; D038202:alpha-Crystallin A Chain / Q000737:chemistry* / Q000378:metabolism*; D038203:alpha-Crystallin B Chain / Q000737:chemistry / Q000378:metabolism
chemical_list: D000089:Acetic Anhydrides; D003459:Crystallins; D018832:Molecular Chaperones; D050505:Mutant Proteins; D038202:alpha-Crystallin A Chain; D038203:alpha-Crystallin B Chain; D005973:Glutamine; C031800:acetic anhydride; D014364:Tryptophan; D008239:Lysine