Purification and N‐terminal amino acid sequence of the human T lymphocyte CD2 (T11) surface antigen

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Abstract
CD2 (the sheep erythrocyte receptor) is a surface antigen of human T lymphocytes. A role for CD2 in T cell function has been implicated from the observation that antibodies against CD2 are capable of transmitting both positive and negative signals for cell growth. Biochemically, the molecule has been identified as a broad band on sodium dodecyl sulfate (SDS)‐polyacrylamide gels of about 50–58 kDa. This communication demonstrates that CD2 contains N‐linked carbohydrate as endo‐β‐N‐acetylglucosaminidase F digestion reduced its apparent mol. mass to a compact band of 40 kDa. CD2 was purified from the T leukemia cell line J6 by immunoaffinity chromatography and preparative SDS‐polyacrylamide gel electrophoresis (PAGE). Four bands of 52, 54, 56 and 58 kDa could be distinguished in the immunoaffinity‐purified protein which formed a broad zone on SDS‐PAGE extending from about 45 to 58 kDa. Preparative SDS‐PAGE yielded a product suitable for determining the N‐terminal amino acid sequence. Assignments were made for the first 26 (excluding the 23rd) residues and the sequence identified a novel polypeptide.