AMINO-ACID SEQUENCE OF THE VH REGION OF HUMAN MYELOMA CRYO-IMMUNOGLOBULIN IGG HIL

We have determined the complete amino acid sequence of the variable region of the heavy chain (VH) from a human myeloma cryoimmunoglobulin, IgGl Hil. The N-terminal sequence was determined by automatic procedures after specific removal of the a-amino terminal pyroglutamic acid by calf liver pyroglutamate aminopeptidase. This deblocking procedure was applied to whole heavy chain and to a heavy chain fragment (positions 1-99) derived by acid treatment of Fab Hil. CNBr fragments spanning residues 35-81 and 84-256 provided two additional starting points for automatic sequencing. The results of these automatic runs gave the sequence from residues 35 to 70 and from 84 to 117. Characterization and sequencing of tryptic peptides were used to complete the C-terminal end sequence of one CNBr fragment (positions 35-81) and to find the sequence of a gap between the two CNBr fragments. The sequence toward the C-terminal end of variable region and the beginning of the constant region was determined on a tryptic peptide spanning residues 99-125. This peptide was sequenced to its C terminus by automatic liquid-phase procedures in the presence of polybrene. In addition, tryptic peptides covering the whole extent of the variable region were isolated and characterized to provide further support to the automatic sequence data. The proposed sequence of the variable region indicates that it may be assigned to subgroup VHIII. The VL sequence of IgG Hil has been reported [J. A. Lopez de Castro et al. (1978) Biochemistry 17, 1718-1723]. A study of the three-dimensional structure of the Fab fragment from this protein by X-ray diffraction is in progress. © 1979, American Chemical Society. All rights reserved.