Stability and aggregation propensity do not fully account for the association of various germline variable domain gene segments with light chain amyloidosis

Abstract

Variable domain (VL) gene segments exhibit variable tendencies to be associated with light chain amyloidosis (AL). While few of them are very frequent in AL and give rise to most of the amyloidogenic light chains compiled at the sequence databases, other are rarely found among the AL cases. To analyze to which extent these tendencies depend on folding stability and aggregation propensity of the germline VL protein, we characterized VL proteins encoded by four AL-associated germline gene segments and one not associated to AL. We found that the AL-associated germline rVL proteins differ widely in conformational stability and propensity to in vitro amyloid aggregation. While in vitro the amyloid formation kinetics of these proteins correlate well with their folding stabilities, the folding stability does not clearly correlate with their germline's frequencies in AL. We conclude that the association of the VL genes segments to amyloidosis is not determined solely by the folding stability and aggregation propensity of the germline VL protein. Other factors, such as the frequencies of destabilizing mutations and susceptibility to proteolysis, must play a role in determining the light chain amyloidogenicity.

A Substantial Structural Conversion of the Native Monomer Leads to in‐Register Parallel Amyloid Fibril Formation in Light‐Chain Amyloidosis

“…In addition, recent electron‐microscopy studies revealed that fibril cores can be built up according to the same diverse principles as globular protein cores, including, in the same fibril, through hydrophobic, charge, and polar interactions, as illustrated by the recent structure of the tau filament, in which all three types are observed in a single fibril fold. Still, the molecular interactions alone might not be sufficient to account for the important role of the aggregation process in the disease, because it has been shown that the role of the V L genes in amyloidosis is not only determined by the V L protein stability and aggregation propensity, but that the frequencies of destabilizing mutations and susceptibility to proteolysis equally represent determinants for amyloidogenicity . Although we show this arrangement for polymorph A here, the similar regions found in β‐strand secondary structure for polymorph B (Figure A) strongly suggest that polymorph B, for which no 13 C: 15 N mixed preparations showing a single polymorph could be obtained, also adopts a similar fold.…”

The CDR1 and Other Regions of Immunoglobulin Light Chains are Hot Spots for Amyloid Aggregation

“…It has been shown that this protein efficiently forms fibrils under near physiological conditions of temperature, pH and ionic strength 17,53 . In addition, it was recently demonstrated that 6aJL2 and its point mutant 6aJL2-R25G are the proteins most prone to aggregation among a group of six rV L proteins encoded by the germ line of five V L gene segments that are associated to amyloid deposition 24 . It should be noted that 6aJL2 has the germline sequence of subgroup λ6, the family of light chains that shows the strongest association with amyloid deposition 18–21,24 .…”

“…In addition, it was recently demonstrated that 6aJL2 and its point mutant 6aJL2-R25G are the proteins most prone to aggregation among a group of six rV L proteins encoded by the germ line of five V L gene segments that are associated to amyloid deposition 24 . It should be noted that 6aJL2 has the germline sequence of subgroup λ6, the family of light chains that shows the strongest association with amyloid deposition 18–21,24 . Hence, sequence elements contained in the segment Ile30-Gln37 are obvious candidates for the driver of the amyloid aggregation of 6aJL2.…”

“…With only one clinically proven exception 23 , all monoclonal λ6 light chains identified so far has been shown to be involved in amyloid deposition 22 . Moreover, we have shown that 6aJL2 can form amyloid-like fibrils in physiological relevant conditions of pH, temperature, and ionic strength 24 . These findings suggest that as yet unidentified amyloidogenic sequences encoded in the germline IGLV6-57 could be part of the structural factors that make λ6 light chains highly prone to aggregate as amyloid fibrils 17,24,25 .…”

“…Moreover, we have shown that 6aJL2 can form amyloid-like fibrils in physiological relevant conditions of pH, temperature, and ionic strength 24 . These findings suggest that as yet unidentified amyloidogenic sequences encoded in the germline IGLV6-57 could be part of the structural factors that make λ6 light chains highly prone to aggregate as amyloid fibrils 17,24,25 . Being a protein with germline sequence, 6aJL2 is an ideal model to study the contribution of germline-encoded fibrilogenic sequences to the propensity of the λ6 light chains to aggregate as amyloid.…”