title: C-Terminal truncation affects subunit exchange of human alphaA-crystallin with alphaB-crystallin.
abstract: In human lenses, C-terminal cleavage of alphaA-crystallin at residues 172,168, and 162 have been reported. The effect of C-terminal truncation of alphaA-crystallin on subunit exchange and heterooligomer formation with alphaB-crystallin and homooligomer formation with native alphaA-crystallin is not known. We have conducted fluorescence resonance energy transfer studies which have shown that the rates of subunit exchange of alphaA(1-172 )and alphaA(1-168 )with alphaB-wt were two-fold lower than for alphaA-wt interacting with alphaB-wt. The subunit exchange rate between alphaA(1-162) and alphaB-wt was six-fold lower. These data suggest that cleavage of the C-terminal residues could significantly affect heterooligomerization. On the other hand, the subunit exchange rates between alphaA-wt and the truncated alphaA-crystallins were either unchanged or only slightly decreased, which suggest that homooligomerization may not be significantly influenced by C-terminal truncation. The main conclusion from this study is that cleavage of C-terminal residues of alphaA-crystallin including the nine residues of the flexible tail is expected to significantly affect the formation of heteroaggregates. Reconstitution experiments showed that the presence of an intact C-terminus is essential for the formation of fully integrated heteroaggregates with equal proportion of alphaA and alphaB subunits.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Biomedical Research Center I B405C-Slot 516, Little Rock, AR 72205, USA.
authors.forename: Latha S
authors.initials: LS
authors.lastname: Kallur
authors.forename: Atya
authors.initials: A
authors.lastname: Aziz
authors.forename: Edathara C
authors.initials: EC
authors.lastname: Abraham
mesh_terms: D002851:Chromatography, High Pressure Liquid; D004591:Electrophoresis, Polyacrylamide Gel; D005453:Fluorescence; D031541:Fluorescence Resonance Energy Transfer; D006801:Humans; D007700:Kinetics; D008970:Molecular Weight; D050505:Mutant Proteins / Q000378:metabolism*; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D021122:Protein Subunits / Q000378:metabolism*; D013997:Time Factors; D038202:alpha-Crystallin A Chain / Q000737:chemistry* / Q000378:metabolism*; D038203:alpha-Crystallin B Chain / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D050505:Mutant Proteins; D021122:Protein Subunits; D038202:alpha-Crystallin A Chain; D038203:alpha-Crystallin B Chain