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Mutations in specific structural regions of immunoglobulin light chains are associated with free light chain levels in patients with AL amyloidosis.

Poshusta TL, Sikkink LA, Leung N, Clark RJ, Dispenzieri A, Ramirez-Alvarado M - PLoS ONE (2009)

Bottom Line: Among patients with AL, the levels of circulating immunoglobulin free light chain varies greatly, but even patients with very low levels can have very advanced amyloid deposition.Our results show that in specific secondary structure elements, there are significant differences in the number of non-conservative mutations between normal and AL sequences.AL sequences from patients with different levels of secreted light chain have distinct differences in the location of non-conservative mutations, suggesting that for patients with very low levels of light chains and advanced amyloid deposition, the location of non-conservative mutations rather than the amount of free light chain in circulation may determine the amyloidogenic propensity of light chains.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Molecular Biology, College of Medicine, Mayo Clinic, Rochester, Minnesota, United States of America.

ABSTRACT

Background: The amyloidoses are protein misfolding diseases characterized by the deposition of amyloid that leads to cell death and tissue degeneration. In immunoglobulin light chain amyloidosis (AL), each patient has a unique monoclonal immunoglobulin light chain (LC) that forms amyloid deposits. Somatic mutations in AL LCs make these proteins less thermodynamically stable than their non-amyloidogenic counterparts, leading to misfolding and ultimately the formation of amyloid fibrils. We hypothesize that location rather than number of non-conservative mutations determines the amyloidogenicity of light chains.

Methodology/principal findings: We performed sequence alignments on the variable domain of 50 kappa and 91 lambda AL light chains and calculated the number of non-conservative mutations over total number of patients for each secondary structure element in order to identify regions that accumulate non-conservative mutations. Among patients with AL, the levels of circulating immunoglobulin free light chain varies greatly, but even patients with very low levels can have very advanced amyloid deposition.

Conclusions: Our results show that in specific secondary structure elements, there are significant differences in the number of non-conservative mutations between normal and AL sequences. AL sequences from patients with different levels of secreted light chain have distinct differences in the location of non-conservative mutations, suggesting that for patients with very low levels of light chains and advanced amyloid deposition, the location of non-conservative mutations rather than the amount of free light chain in circulation may determine the amyloidogenic propensity of light chains.

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VL structure.A) Topological Diagram of the protein structure for AF490909 adapted from Schiffer, et al [28]. The two β-sheets of the domains have been separated. Residues that point towards the core are circled. CDR segments are highlighted in yellow. The β-strands have been encased within the arrows and are connected to their respective loops. B) Structural model of a VL (1BRE.pdb) showing CDR regions in pink, β-hairpin between strands D and E in blue and dimer interface in green ribbons.
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pone-0005169-g001: VL structure.A) Topological Diagram of the protein structure for AF490909 adapted from Schiffer, et al [28]. The two β-sheets of the domains have been separated. Residues that point towards the core are circled. CDR segments are highlighted in yellow. The β-strands have been encased within the arrows and are connected to their respective loops. B) Structural model of a VL (1BRE.pdb) showing CDR regions in pink, β-hairpin between strands D and E in blue and dimer interface in green ribbons.

Mentions: The overall structure of the VL is an immunoglobulin fold with 9 β-strands (A, B, C, C′, C″, D, E, F, and G) packed tightly against each other in two antiparallel β sheets joined together by a disulfide bridge. The N- and C- termini strands (A and G, respectively) are parallel [4]. The topology is a form of a Greek key β-barrel. The CDRs form three loops between amino acids 24–34, 50–56 and 89–95 that contain the amino acids that will recognize the antigen (Figure 1). Immunoglobulin quaternary structure consists of two heterodimers formed by the LC and the immunoglobulin heavy chain (HC) interacting together via disulfide bonds. The LC VL domain interacts with the HC variable domain through β-strands C, C′, F and G. The source of sequence variability in LCs comes from combinatorial pairing of the V genes (40 κ and 33 λ) and the J genes (corresponding to strand G or FR4), making it possible to generate about 3000 different LC sequences. In addition, further sequence variation appears from somatic mutations to improve the affinity of the antibody for the antigen.


Mutations in specific structural regions of immunoglobulin light chains are associated with free light chain levels in patients with AL amyloidosis.

Poshusta TL, Sikkink LA, Leung N, Clark RJ, Dispenzieri A, Ramirez-Alvarado M - PLoS ONE (2009)

VL structure.A) Topological Diagram of the protein structure for AF490909 adapted from Schiffer, et al [28]. The two β-sheets of the domains have been separated. Residues that point towards the core are circled. CDR segments are highlighted in yellow. The β-strands have been encased within the arrows and are connected to their respective loops. B) Structural model of a VL (1BRE.pdb) showing CDR regions in pink, β-hairpin between strands D and E in blue and dimer interface in green ribbons.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2664898&req=5

pone-0005169-g001: VL structure.A) Topological Diagram of the protein structure for AF490909 adapted from Schiffer, et al [28]. The two β-sheets of the domains have been separated. Residues that point towards the core are circled. CDR segments are highlighted in yellow. The β-strands have been encased within the arrows and are connected to their respective loops. B) Structural model of a VL (1BRE.pdb) showing CDR regions in pink, β-hairpin between strands D and E in blue and dimer interface in green ribbons.
Mentions: The overall structure of the VL is an immunoglobulin fold with 9 β-strands (A, B, C, C′, C″, D, E, F, and G) packed tightly against each other in two antiparallel β sheets joined together by a disulfide bridge. The N- and C- termini strands (A and G, respectively) are parallel [4]. The topology is a form of a Greek key β-barrel. The CDRs form three loops between amino acids 24–34, 50–56 and 89–95 that contain the amino acids that will recognize the antigen (Figure 1). Immunoglobulin quaternary structure consists of two heterodimers formed by the LC and the immunoglobulin heavy chain (HC) interacting together via disulfide bonds. The LC VL domain interacts with the HC variable domain through β-strands C, C′, F and G. The source of sequence variability in LCs comes from combinatorial pairing of the V genes (40 κ and 33 λ) and the J genes (corresponding to strand G or FR4), making it possible to generate about 3000 different LC sequences. In addition, further sequence variation appears from somatic mutations to improve the affinity of the antibody for the antigen.

Bottom Line: Among patients with AL, the levels of circulating immunoglobulin free light chain varies greatly, but even patients with very low levels can have very advanced amyloid deposition.Our results show that in specific secondary structure elements, there are significant differences in the number of non-conservative mutations between normal and AL sequences.AL sequences from patients with different levels of secreted light chain have distinct differences in the location of non-conservative mutations, suggesting that for patients with very low levels of light chains and advanced amyloid deposition, the location of non-conservative mutations rather than the amount of free light chain in circulation may determine the amyloidogenic propensity of light chains.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Molecular Biology, College of Medicine, Mayo Clinic, Rochester, Minnesota, United States of America.

ABSTRACT

Background: The amyloidoses are protein misfolding diseases characterized by the deposition of amyloid that leads to cell death and tissue degeneration. In immunoglobulin light chain amyloidosis (AL), each patient has a unique monoclonal immunoglobulin light chain (LC) that forms amyloid deposits. Somatic mutations in AL LCs make these proteins less thermodynamically stable than their non-amyloidogenic counterparts, leading to misfolding and ultimately the formation of amyloid fibrils. We hypothesize that location rather than number of non-conservative mutations determines the amyloidogenicity of light chains.

Methodology/principal findings: We performed sequence alignments on the variable domain of 50 kappa and 91 lambda AL light chains and calculated the number of non-conservative mutations over total number of patients for each secondary structure element in order to identify regions that accumulate non-conservative mutations. Among patients with AL, the levels of circulating immunoglobulin free light chain varies greatly, but even patients with very low levels can have very advanced amyloid deposition.

Conclusions: Our results show that in specific secondary structure elements, there are significant differences in the number of non-conservative mutations between normal and AL sequences. AL sequences from patients with different levels of secreted light chain have distinct differences in the location of non-conservative mutations, suggesting that for patients with very low levels of light chains and advanced amyloid deposition, the location of non-conservative mutations rather than the amount of free light chain in circulation may determine the amyloidogenic propensity of light chains.

Show MeSH
Related in: MedlinePlus