Certain types of human light chains have the propensity to deposit pathologically as amyloid fibrils as evidenced by the preferential association of monoclonal lambda 6 proteins with AL amyloidosis. However, the molecular features that render such proteins amyloidogenic have not been elucidated. Based upon the demonstrated relationship between the thermodynamic stability of light chains and their propensity to aggregate in vitro, we have initiated studies where the thermodynamic properties and fibrillogenic potential of two recombinant (r) V lambda 6 molecules were compared. The first protein was generated from cDNA cloned from marrow-derived plasma cells from a patient (Wil) who had AL amyloidosis and renal amyloid deposits; the second was from a patient (Jto) with multiple myeloma in whom the lambda 6 protein was deposited not as amyloid but in the form of renal tubular casts. The thermodynamic stabilities of rV lambda 6Wil and -Jto were determined from chaotropic and thermal denaturation studies. Based upon the Delta GH2O, Delta H, Delta G25 degrees C, Tm, and Cm values, the rV lambda 6Wil was less stable than its nonamyloidogenic counterpart, rV lambda 6Jto. Measurement of fibril formation using a novel in vitro fibril forming assay demonstrated that although both rV lambda 6 proteins formed fibrils in vitro, Wil had a shorter lag time and exhibited faster kinetics under physiologic conditions. Comparative amino acid sequence analyses of these two components and other lambda 6 amyloid-associated light chains revealed that the Jto protein had certain primary structural features that we posit contributed to its increased stability and thus rendered this protein nonamyloidogenic. Our studies provide the first evidence that stabilizing interactions within the V L domain can influence the kinetics of light chain fibrillogenicity.

The endoplasmic reticulum is a major compartment of protein biogenesis in the cell, dedicated to production of secretory, membrane and organelle proteins. The secretome has distinct structural and post-translational characteristics, since folding in the ER occurs in an environment that is distinct in terms of its ionic composition, dynamics and requirements for quality contol. The folding machinery in the ER therefore includes chaperones and folding enzymes that introduce, monitor and react to disulfide bonds, glycans, and fluctuations of luminal calcium. We describe the major chaperone networks in the lumen and discuss how they have distinct modes of operation that enable cells to accomplish highly efficient production of the secretome.

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