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An unusual papain cleavage of a human IgG1 (lambda) myeloma protein (Mot)
Abstract:
An IgGl (lambda) protein which showed a unique susceptibility towards papain digestion was isolated from the serum of a patient (Mot) with multiple myeloma. The Fab fragments of this protein were degraded rapidly into smaller peptides via an Fb fragment [Gall & D'Eustachio (1972), Biochemistry 11, 4621-4628], which corresponded to the constant domains (Cl-Chl). Structural analysis of the isolated Fab fragment, which consisted of the intact L-chain, a 17,000 and a 5000 mol. wt peptide fragment, indicated that the initial cleavage site was located in the vicinity of the second hypervariable region of the Fd fragment. Examination of the partial amino acid sequences of the Mot H-chain suggested that the variable region of the H-chain may be a hitherto unknown hybrid of subgroups I and III. This particular structure seems to have made the Fab fragment highly susceptible to papain. In the course of the present study, we also found in the papain digests of several human IgG proteins an 'intermediate' 5S fragment, which had previously been reported exclusively for the papain digest of rabbit IgG.
Insights
Researchers identified a unique immunoglobulin G (IgG) protein from a multiple myeloma patient that rapidly degraded after papain digestion. This susceptibility was linked to an unusual hybrid variable region in the heavy chain.
Area of Science:
- Immunology
- Protein Chemistry
- Molecular Biology
Background:
- Immunoglobulin G (IgG) proteins are crucial for the adaptive immune system.
- Papain digestion is a standard method for fragmenting IgG antibodies.
- Multiple myeloma is a cancer of plasma cells, often associated with abnormal protein production.
Purpose of the Study:
- To investigate the unique papain digestion susceptibility of an isolated IgG (lambda) protein from a multiple myeloma patient (Mot).
- To structurally analyze the Fab fragments and identify the cleavage sites.
- To determine the molecular basis for the observed susceptibility.
Main Methods:
- Isolation and purification of IgG (lambda) protein from patient serum.
- Papain digestion of the isolated IgG protein.
- Structural analysis of Fab fragments, including molecular weight determination.
- Partial amino acid sequencing of the heavy (H) chain.
Main Results:
- The isolated IgG (lambda) protein exhibited rapid degradation of Fab fragments upon papain digestion.
- Cleavage occurred near the second hypervariable region of the Fd fragment.
- The heavy chain's variable region appeared to be a novel hybrid of subgroups I and III.
- An intermediate 5S fragment, typically seen in rabbit IgG digests, was also observed in human IgG digests.
Conclusions:
- The unique hybrid variable region structure of the Mot IgG H-chain likely confers increased susceptibility to papain digestion.
- The findings suggest potential structural variations in human IgG that can influence enzymatic cleavage.
- The presence of the 5S fragment in human IgG digests broadens its occurrence beyond rabbit IgG.