Isolation and chemical characterization of the human B29 and mb-1 proteins of the B cell antigen receptor complex

Mol Immunol. 1994 Apr;31(6):419-27. doi: 10.1016/0161-5890(94)90061-2.


A disulfide-linked heterodimeric antigen from human B leukemia cells was detected by radioimmunoprecipitation and Western blot analysis using a monoclonal antibody (mAb). The mAb was generated against a cell membrane antigen preparation from human B prolymphocytic leukemia cells and found to define an extracellular epitope of the smaller component (beta chain) of a heterodimeric antigen on human B leukemia cells. The antigen from BALL-1, a human B leukemia cell line, and fresh (uncultured) B prolymphocytic leukemia cells was found to consist of a 44-49 kDa (alpha chain) and a 36-40 kDa (beta chain) component. An additional minor component of 34 kDa was detected in the reduced antigen from BALL-1. For chemical identification of the antigen, we isolated the antigen from a Triton X-100 lysate of BALL-1 by immunoaffinity chromatography using the mAb. Determination of the amino-terminal amino acid sequences of the alpha and beta chains unequivocally identified them as the human mb-1 and B29 proteins, respectively. The sequence analyses indicate the molecular heterogeneity of the mb-1 protein and also perhaps the heterogeneity of the B29 protein. We detected three forms of the mb-1 protein which share an identical amino-terminal amino acid sequence and probably two forms of the B29 protein which share an identical amino-terminal sequence. Our sequence data allowed us to establish the authentic amino-terminal amino acid sequence of the human B29 protein which is different from those proposed by others based on cDNA sequence analyses. Comparison of the amino-terminal sequences of the human mb-1 and B29 proteins with those of the mouse mb-1 and B29 proteins showed that the majority of the conserved amino acids in the mb-1 proteins are hydrophobic amino acids. Such conservation of hydrophobic amino acids is not observed in the amino termini of the human and mouse B29 proteins. A beta-tubulin-like protein was found to be co-purified with the mb-1-B29 antigen in the present study. In addition, we found that there is a strong amino acid sequence homology between the microtubule-binding domains of certain human microtubule-associated proteins and an intracellular segment of the human mb-1 protein.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Antigens / chemistry
  • Antigens, CD*
  • B-Lymphocytes / immunology*
  • Blotting, Western
  • CD79 Antigens
  • Disulfides / chemistry
  • Epitopes
  • Humans
  • Leukemia, B-Cell
  • Macromolecular Substances
  • Membrane Glycoproteins / chemistry*
  • Molecular Sequence Data
  • Phosphoproteins / chemistry*
  • Precipitin Tests
  • Receptors, Antigen, B-Cell / chemistry*
  • Sequence Analysis
  • Sequence Homology, Amino Acid
  • Signal Transduction
  • Tubulin / isolation & purification
  • Tumor Cells, Cultured


  • Antigens
  • Antigens, CD
  • CD79 Antigens
  • CD79A protein, human
  • CD79B protein, human
  • Disulfides
  • Epitopes
  • Macromolecular Substances
  • Membrane Glycoproteins
  • Phosphoproteins
  • Receptors, Antigen, B-Cell
  • Tubulin