2Moscow Region Clinics Institute, ul. Shchepkina 61/2, 129110 Moscow, Russia
3Institute of Biological Instrumentation, Russian Academy of Sciences, 142292 Pushchino, Moscow Region, Russia
4Institute of Roentgenology and Radiology, Federal Ministry of Health, Leningradskoe Shosse 70/7, 197701 St. Petersburg, Russia
* To whom correspondence should be addressed.
Received April 2, 2004; Revision received May 24, 2004
Myeloma nephropathy is a disorder characterized by deposition of monoclonal immunoglobulin light chains in the kidneys. The chains deposited form either amyloid fibrils or granular (amorphous) aggregates. Distinct molecular mechanisms leading to the formation of different aggregate types in kidney of patients with multiple myeloma are poorly understood. Here we describe the self-association kinetics of human monoclonal immunoglobulin light chains lambda (GRY) isolated from urine of a patient with multiple myeloma. Under physiological conditions, the isolated light chain exists predominantly in a form of covalent dimer with apparent molecular mass of 50.1 kD. Spectral probe binding, analytical gel filtration, Western blot analysis, and electron microscopy indicate that GRY dimer aggregation occurs via two different pathways producing either amyloid fibrils or amorphous aggregates depending on microenvironment. Incubation of GRY (25 µM) for 4-14 days at 37°C in phosphate buffered saline (PBS), pH 7.0, or in PBS containing urea (0.8 M), pH 6.5, leads to amyloid fibril formation. Under electron microscopy, the fibrils show unbranched thread-like structures, ~ 60-80 × 1000 Å in size, which can bind thioflavin T and Congo Red. GRY maintained in acetate buffer, pH 3.5, forms granular aggregates. The structure of GRY oligomers formed during the early stage of amyloid fibril formation (1-4 days) has been examined by means of protein cross-linking with homobifunctional reagents. These oligomers are predominantly trimers and tetramers.
KEY WORDS: immunoglobulin light chains, amyloidosis, protein aggregation, multiple myeloma