title: Deoxycholate induced tetramer of αA-crystallin and sites of phosphorylation: fluorescence correlation spectroscopy and femtosecond solvation dynamics.
abstract: Structure and dynamics of acrylodan labeled αA-crystallin tetramer formed in the presence of a bile salt (sodium deoxycholate, NaDC) has been studied using fluorescence correlation spectroscopy (FCS) and femtosecond up-conversion techniques. Using FCS it is shown that, the diffusion constant (D(t)) of the αA-crystallin oligomer (mass ~800 kDa) increases from ~35 μm(2) s(-1) to ~68 μm(2) s(-1). This corresponds to a decrease in hydrodynamic radius (r(h)) from ~6.9 nm to ~3.3 nm. This corresponds to about 10-fold decrease in molecular mass to ~80 kDa and suggests formation of a tetramer (since mass of αA-crystallin monomer is ~20 kDa). The steady state emission maximum and average solvation time (<τ(s)>) of acrylodan labeled at cysteine 131 position of αA-crystallin is markedly affected on addition of NaDC, while the tryptophan (trp-9) becomes more exposed. This suggests that NaDC binds near the cys-131 and makes the terminal region of αA-crystallin exposed. This may explain the enhanced auto-phosphorylation activity of αA-crystallin near the terminus of the 173 amino acid protein (e.g., at the threonine 13, serine 45, or serine 169 and 172) and suggests that phosphorylation at ser-122 (close to cys-131) is relatively less important.
authors.affiliation: Dr. B. C. Guha Centre for Genetic Engineering and Biotechnology and Department of Biotechnology, University of Calcutta, Ballygunge Circular Road, Kolkata-700019, India.
authors.forename: Aritra
authors.initials: A
authors.lastname: Chowdhury
authors.forename: Supratik
authors.initials: S
authors.lastname: Sen Mojumdar
authors.forename: Aparajita
authors.initials: A
authors.lastname: Choudhury
authors.forename: Rajat
authors.initials: R
authors.lastname: Banerjee
authors.forename: Kali Pada
authors.initials: KP
authors.lastname: Das
authors.forename: Dibyendu Kumar
authors.initials: DK
authors.lastname: Sasmal
authors.forename: Kankan
authors.initials: K
authors.lastname: Bhattacharyya
mesh_terms: D001665:Binding Sites; D003840:Deoxycholic Acid / Q000737:chemistry*; D010766:Phosphorylation; D012995:Solubility; D013050:Spectrometry, Fluorescence; D013816:Thermodynamics; D013997:Time Factors; D038202:alpha-Crystallin A Chain / Q000737:chemistry*
chemical_list: D038202:alpha-Crystallin A Chain; D003840:Deoxycholic Acid