In vivo modification of the C-terminal lysine of human lens alphaB-crystallin.
Both the structural and chaperone-like properties of lens alpha-crystallins have been implicated in maintaining lens transparency. Modifications of lens alpha-crystallins may lead to formation of cataract by affecting the close-packing of the crystallins or by reducing the chaperone-like activity of the alpha-crystallins. A previously unreported modified alphaB-crystallin, whose molecular weight is 72 u greater than unmodified alphaB-crystallin, has been isolated from human lenses by size exclusion chromatography, reversed phase HPLC and ion exchange HPLC. Approximately one nanomole of this modified alphaB-crystallin was obtained from each of five human eye lenses. Molecular weight determinations of peptides produced by digestion with trypsin or endoproteinase Asp-N showed that the modification is in the C-terminal region of alphaB-crystallin. The fragmentation pattern of peptides from the C-terminal region, analysed by tandem mass spectrometry, located the modification of the epsilon-amino group of the C-terminal lysine. The elemental composition of this modification, determined from its exact mass, is C3H4O2. Because this modification decreases the net charge of alphaB-crystallin by one unit, and because the C-terminus has been implicated in the chaperone activity attributed to alphaB-crystallin, this modification at Lys 175 may have a significant role in cataractogenesis.
Lin
P
P
Department of Chemistry, University of Nebraska, Lincoln, Nebraska, 68588-0304, USA.
Smith
D L
DL
Smith
J B
JB
D000328:Adult; D000368:Aged; D002386:Cataract / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D002852:Chromatography, Ion Exchange; D003459:Crystallins / Q000032:analysis / Q000737:chemistry*; D006801:Humans; D007908:Lens, Crystalline / Q000378:metabolism*; D013058:Mass Spectrometry; D008875:Middle Aged; D018832:Molecular Chaperones; D008970:Molecular Weight
D003459:Crystallins; D018832:Molecular Chaperones