Phosphoproteins of the chicken eggshell calcified layer

Proteomics. 2007 Jan;7(1):106-15

Phosphoproteins of the chicken eggshell calcified layer

Karlheinz Mann, Dr. *, Jesper V. Olsen, Boris Maek, Florian Gnad, Matthias Mann
Max-Planck-Institute for Biochemistry, Department of Proteomics and Signal Transduction, Martinsried, Germany
email: Karlheinz Mann (mann@biochem.mpg.de)

*Correspondence to Karlheinz Mann, Max-Planck-Institut für Biochemie, Abteilung Proteomics und Signaltransduktion, Am Klopferspitz 18, D-82152 Martinsried, Germany Fax: +49-89-8578-2219

The chicken eggshell matrix is a complex mixture of proteins and proteoglycans. It also contains phosphoproteins that are thought to affect mineralization of the matrix. Several of the matrix phosphoproteins, such as the major component osteopontin, have already been identified as phosphoproteins in other tissues, but the phosphorylation status of the eggshell matrix forms was unknown. The phosphopeptides, obtained after cleavage of the matrix proteins with several different cleavage methods, were enriched by anion-exchange chromatography and reversible binding to titanium oxide and identified by LC-MSn or pseudo-MSn analysis following neutral loss scanning. Altogether we identified 39 phosphorylated matrix proteins, 22 of which were not known to be phosphorylated before. Eight of the proteins were identified as eggshell matrix components for the first time. Together these proteins contained more than 150 different phosphorylation sites, 103 of which were determined with high confidence. Among the major phosphorylated proteins of the chicken eggshell matrix were osteopontin and the eggshell-specific proteins ovocleidin-17, ovocleidin-116, and ovocalyxin-32.

Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2120/2006/pro200600635_s.pdf