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Profiling of the CD4 Receptor Complex Proteins

G. I. Krotov1*, M. P. Krutikova1, V. G. Zgoda2, and A. V. Filatov1

1National Research Center Institute of Immunology, Federal Biomedical Agency of Russia, Kashirskoe Shosse 24/2, 115478 Moscow, Russia; fax: (499) 617-7765; E-mail: grkrotov@rambler.ru

2Orekhovich Institute of Biomedical Chemistry, Russian Academy of Medical Sciences, Pogodinskaya ul. 10, 119121 Moscow, Russia; fax: (495) 246-1641; E-mail: vic@ibmn.msk.ru

* To whom correspondence should be addressed.

Received May 23, 2007; Revision received July 3, 2007
Intermolecular complexes produced by the CD4 molecule were studied. To preserve the integrity of weak protein-protein interactions of the CD4 antigen, cells were lysed in a mild nonionic detergent Brij97. Protein constituents of the complex were identified by our previously proposed fluorescence immunoprecipitation assay with subsequent mass spectrometry. In total, 26 proteins associated with CD4 were identified on CEM cells. The CD4 complex included the following major components: tyrosine phosphatase CD45, transferrin receptor CD71, tyrosine kinase Lck, and a lymphocyte phosphatase-associated phosphoprotein LPAP. The CD4 complex also contained some components of cytoskeleton and heat shock proteins. The association between CD4, CD71, and CD45 molecules was confirmed by immunoblotting. The CD4 complexes were not detected on the U937 myeloid cells lacking Lck and LPAP. We attempted to quantitatively characterize the CD4 complex composition.
KEY WORDS: protein complexes, nonionic detergents, immunoprecipitation, mass spectrometry, CD4

DOI: 10.1134/S0006297907110077