Occurrence of heavy chain of 7S IgM half-molecule whose NH2-terminal sequence is identical with that of kappa light chain sequence in patients with Waldenstrom macroglobulinemia.
We report a rare case of a half molecule 7S IgM (HM 7SIgM) consisting of a unique mu heavy chain and kappa light chain found in blood and urine samples from a patient with primary Waldenstrom macroglobulinemia. A 64kDa abnormal immunoglobulin was detected in serum and urine by immunoblot method, and purified by a two-dimensional SDS-PAGE after separation from IgG and albumin fractions on gel filtration. NH2-terminal amino acid sequence analysis of the heavy chain revealed that residues 1-20 were identical to those of the NH2-terminal region of kappa light chain derived from the same patient. This sequence was then followed by a sequence that could not be identified by a computer homology search on the protein database. Using polypeptide segments obtained from the unique mu chain by digestion with endopeptidase, we identified a sequence spanning from residue 127 in the variable region of the known mu chain to residue 19 in the known CH1 domain and a sequence spanning from residues 67-82 in the heavy chain variable region class II. From these results, we concluded that the 64 kDa protein was an abnormal half molecule 7S IgM consisting of a kappa light chain and a unique mu heavy chain of 35 kDa polypeptide in which the NH2-terminal 20 amino acids were replaced by 20 amino acids derived from the sequence of kappa light chain in the NH2-terminal region.
Imoto
M
M
Department Central Clinical Laboratory, Kinki University Hospital, Osakasayama, Osaka, Japan.
Ishikawa
K
K
Yamamoto
K
K
Sinohara
H
H
Irimajiri
K
K
Kubo
N
N
Sakurabayashi
I
I
Horiuchi
A
A
Akiyama
T
T
Ohba
Y
Y
Furuta
I
I
D000595:Amino Acid Sequence; D006801:Humans; D007122:Immunoelectrophoresis; D007143:Immunoglobulin Heavy Chains / Q000737:chemistry*; D007147:Immunoglobulin Light Chains / Q000737:chemistry*; D007075:Immunoglobulin M / Q000737:chemistry*; D007145:Immunoglobulin kappa-Chains / Q000737:chemistry*; D008297:Male; D008875:Middle Aged; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010206:Papain / Q000378:metabolism; D016415:Sequence Alignment; D008258:Waldenstrom Macroglobulinemia / Q000378:metabolism*
D007143:Immunoglobulin Heavy Chains; D007147:Immunoglobulin Light Chains; D007075:Immunoglobulin M; D007145:Immunoglobulin kappa-Chains; D010206:Papain