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Protein Science, Vol 1, Issue 5 601-608, Copyright © 1992 by Cold Spring Harbor Laboratory Press
ARTICLE |
J. B. SMITH, Y. SUN, D. L. SMITH and B. GREEN
Department of Medicinal Chemistry and Pharmacognosy, Purdue University, West Lafayette, Indiana 47907
A combination of mass spectrometric techniques has been used to investigate the amino acid sequence and posttranslational modificatios of {alpha}B-crystallin isolated from bovine lenses by gel filtration chromatography and reversed-phase high performance liquid chromatography. Chromatographic fractions were analyzed by electrospray ionization mass spectrometry to determine the homogeneity and molecular weights of proteins in the fractions. The {alpha}B-crystallin primary gene product, its mono-and diphosphorylated forms, its N- and C-terminal truncated forms, as well as other lens proteins unrelated to the {alpha}B-crystallins were identified by their molecular weights. Detailed information about the sites of phosphorylation, as well as evidence supporting reassignment of Asn to Asp at position 80, was obtained by analyzing proteolytic digests of these proteins by fast atom bombardment mass spectrometry. Results of this investigation indicate that {alpha}B-crystallin is phosphorylated in vivo at Ser 45, Ser 59, and either Ser 19 or 21. From the specificity of phosphorylation of {alpha}-crystallins, it appears that there may be two different kinases responsible for their phosphorylation.
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