Mass spectrometry characterization of light chain fragmentation sites in cardiac AL amyloidosis: insights into the timing of proteolysis

J Biol Chem. 2020 Dec 4;295(49):16572-16584. doi: 10.1074/jbc.RA120.013461. Epub 2020 Sep 20.

Abstract

Amyloid fibrils are polymeric structures originating from aggregation of misfolded proteins. In vivo, proteolysis may modulate amyloidogenesis and fibril stability. In light chain (AL) amyloidosis, fragmented light chains (LCs) are abundant components of amyloid deposits; however, site and timing of proteolysis are debated. Identification of the N and C termini of LC fragments is instrumental to understanding involved processes and enzymes. We investigated the N and C terminome of the LC proteoforms in fibrils extracted from the hearts of two AL cardiomyopathy patients, using a proteomic approach based on derivatization of N- and C-terminal residues, followed by mapping of fragmentation sites on the structures of native and fibrillar relevant LCs. We provide the first high-specificity map of proteolytic cleavages in natural AL amyloid. Proteolysis occurs both on the LC variable and constant domains, generating a complex fragmentation pattern. The structural analysis indicates extensive remodeling by multiple proteases, largely taking place on poorly folded regions of the fibril surfaces. This study adds novel important knowledge on amyloid LC processing: although our data do not exclude that proteolysis of native LC dimers may destabilize their structure and favor fibril formation, the data show that LC deposition largely precedes the proteolytic events documentable in mature AL fibrils.

Keywords: amyloid; amyloid fibrils; cardiomyopathy; fibril; mass spectrometry (MS); protein aggregation; protein conformation; protein structure; proteolysis; proteomics; structural biology.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Amyloid / chemistry*
  • Amyloid / metabolism
  • Chromatography, High Pressure Liquid
  • Electrophoresis, Gel, Two-Dimensional
  • Humans
  • Immunoglobulin Light Chains / chemistry
  • Immunoglobulin Light Chains / metabolism
  • Immunoglobulin Light-chain Amyloidosis / metabolism
  • Immunoglobulin Light-chain Amyloidosis / pathology*
  • Myocardium / metabolism*
  • Peptides / analysis
  • Protein Structure, Secondary
  • Protein Structure, Tertiary
  • Proteolysis
  • Tandem Mass Spectrometry

Substances

  • Amyloid
  • Immunoglobulin Light Chains
  • Peptides

Associated data

  • PDB/6MG4
  • PDB/5MUH