Tertiary structure of an amyloid immunoglobulin light chain protein: A proposed model for amyloid fibril formation

Norbert Schormann, Jill R. Murrell, Juris J. Liepnieks, Merrill D. Benson

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Abstract

An immunoglobulin light chain protein was isolated from the urine of an individual (BRE) with systemic amyloidosis. Complete amino acid sequence of the variable region of the light chain (V(L)) protein established it as a κ I, which when compared with other κ I amyloid associated proteins had unique residues, including Ile-34, Leu-40, and Tyr-71. To study the tertiary structure, BRE V(L) was expressed in Escherichia colt by using a PCR product amplified from the patient BRE's bone marrow DNA. The PCR product was ligated into pCZ11, a thermal-inducible replication vector. Recombinant BRE V(L) was isolated, purified to homogeneity, and crystallized by using ammonium sulfate as the precipitant. Two crystal forms were obtained. In crystal form I the BRE V(L) κ domain crystallizes as a dimer with unit cell constants isomorphous to previously published κ protein structures. Comparison with a nonamyloid V(L) κ domain from patient REI, identified significant differences in position of residues in the hypervariable segments plus variations in framework region (FR) segments 40-46 (FR2) and 66-67 (FR3). In addition, positional differences can be seen along the two types of local diads, corresponding to the monomer-monomer and dimer-dimer interfaces. From the packing diagram, a model for the amyloid light chain (AL) fibril is proposed based on a pseudohexagonal spiral structure with a rise of approximately the width of two dimers per 360° turn. This spiral structure could be consistent with the dimensions of amyloid fibrils as determined by electron microscopy.

Original languageEnglish (US)
Pages (from-to)9490-9494
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Volume92
Issue number21
DOIs
StatePublished - Oct 10 1995

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Keywords

  • amyloid light chain amyloidosis
  • x-ray crystallography

ASJC Scopus subject areas

  • Genetics
  • General

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