Hereditary Lysozyme Amyloidosis Variant p.Leu102Ser Associates with Unique Phenotype.

Lysozyme amyloidosis (ALys) is a rare form of hereditary amyloidosis that typically manifests with renal impairment, gastrointestinal (GI) symptoms, and sicca syndrome, whereas cardiac involvement is exceedingly rare and neuropathy has not been reported. Here, we describe a 40-year-old man with renal impairment, cardiac and GI symptoms, and peripheral neuropathy. Renal biopsy specimen analysis revealed amyloidosis with extensive involvement of glomeruli, vessels, and medulla. Amyloid was also detected in the GI tract. Echocardiographic and electrocardiographic findings were consistent with cardiac involvement. Proteomic analysis of Congo red-positive renal and GI amyloid deposits detected abundant lysozyme C protein. DNA sequencing of the lysozyme gene in the patient and his mother detected a heterozygous c.305T>C alteration in exon 3, which causes a leucine to serine substitution at codon 102 (Human Genome Variation Society nomenclature: p.Leu102Ser; legacy designation: L84S). We also detected the mutant peptide in the proband's renal and GI amyloid deposits. PolyPhen analysis predicted that the mutation damages the encoded protein. Molecular dynamics simulations suggested that the pathogenesis of ALys p.Leu102Ser is mediated by shifting the position of the central ß-hairpin coordinated with an antiparallel motion of the C-terminal helix, which may alter the native-state structural ensemble of the molecule, leading to aggregation-prone intermediates.

Amyloidogenic lysozymes accumulate in the endoplasmic reticulum accompanied by the augmentation of ER stress signals.

BACKGROUND: Naturally occurring single mutants, I56T, F57I, W64R and D67H of lysozyme in human, have been known to form abnormal protein aggregates (amyloid fibrils) and to accumulate in several organs, including the liver, spleen and kidney, resulting in familial systemic amyloidosis. These human pathogenic lysozyme variants are considered to raise subtle conformational changes compared to the wild type. METHODS: Here we examined the effects of the aberrant mutant lysozymes I56T, F57I, W64R and D67H, each of which possesses a point mutation in its molecule, on a cultured human cell line, HEK293, in which the genes were individually integrated and overexpressed. RESULTS: Western blot analyses showed lesser amounts of these variant proteins in the medium compared to the wild type, but they were abundant in the cell pellets, indicating that the modified lysozyme proteins were scarcely secreted into the medium but were retained in the cells. Immunocytochemistry revealed that these proteins resided in restricted regions which were stained by an endoplasmic reticulum (ER) marker. Moreover, the overexpression of the mutant lysozymes were accompanied by marked increases in XBP-1s and GRP78/BiP, which are downstream agents of the IRE1α signaling pathway responding to the unfolded protein response (UPR) upon ER stress. RNAi for the mutant lysozymes' expression greatly suppressed the increases of these agents. CONCLUSIONS AND GENERAL SIGNIFICANCE: Our results suggest that the accumulation of pathogenic lysozymes in the ER caused ER stress and the UPR response mainly via the IRE1α pathway.

A non-natural variant of human lysozyme (I59T) mimics the in vitro behaviour of the I56T variant that is responsible for a form of familial amyloidosis.

We report here the detailed characterisation of a non-naturally occurring variant of human lysozyme, I59T, which possesses a destabilising point mutation at the interface of the alpha- and beta-domains. Although more stable in its native structure than the naturally occurring variants that give rise to a familial form of systemic amyloidosis, I59T possesses many attributes that are similar to these disease-associated species. In particular, under physiologically relevant conditions, I59T populates transiently an intermediate in which a region of the structure unfolds cooperatively; this loss of global cooperativity has been suggested to be a critical feature underlying the amyloidogenic nature of the disease-associated lysozyme variants. In the present study, we have utilised this variant to provide direct evidence for the generic nature of the conformational transition that precedes the ready formation of the fibrils responsible for lysozyme-associated amyloid disease. This non-natural variant can be expressed at higher levels than the natural amyloidogenic variants, enabling, for example, singly isotopically labelled protein to be generated much more easily for detailed structural studies by multidimensional NMR spectroscopy. Moreover, we demonstrate that the I59T variant can readily form fibrils in vitro, similar in nature to those of the amyloidogenic I56T variant, under significantly milder conditions than are needed for the wild-type protein.

Hereditary lysozyme amyloidosis: spontaneous hepatic rupture (15 years apart) in mother and daughter. role of emergency liver transplantation.

Hepatic rupture is a rare condition, and treatment options are very limited. We report a case of hepatic rupture secondary to hereditary lysozyme amyloidosis that was successfully treated by liver transplantation. The mother of this patient had presented in an identical fashion 15 years earlier in the pretransplant era and died very rapidly.

Reduced global cooperativity is a common feature underlying the amyloidogenicity of pathogenic lysozyme mutations.

One of the 20 or so human amyloid diseases is associated with the deposition in vital organs of full-length mutational variants of the antibacterial protein lysozyme. Here, we report experimental data that permit a detailed comparison to be made of the behaviour of two of these amyloidogenic variants, I56T and D67H, under identical conditions. Hydrogen/deuterium exchange experiments monitored by NMR and mass spectrometry reveal that, despite their different locations and the different effects of the two mutations on the structure of the native state of lysozyme, both mutations cause a cooperative destabilisation of a remarkably similar segment of the structure, comprising in both cases the beta-domain and the adjacent C-helix. As a result, both variant proteins populate transiently a closely similar, partially unstructured intermediate in which the beta-domain and the adjacent C-helix are substantially and simultaneously unfolded, whereas the three remaining alpha-helices that form the core of the alpha-domain still have their native-like structure. We show, in addition, that the binding of a camel antibody fragment, cAb-HuL6, which was raised against wild-type lysozyme, restores to both variant proteins the stability and cooperativity characteristic of the wild-type protein; as a consequence, it inhibits the formation of amyloid fibrils by both variants. These results indicate that the reduction in global cooperativity, and the associated ability to populate transiently a specific, partly unfolded intermediate state under physiologically relevant conditions, is a common feature underlying the behaviour of these two pathogenic mutations. The formation of intermolecular interactions between lysozyme molecules that are in this partially unfolded state is therefore likely to be the fundamental trigger of the aggregation process that ultimately leads to the formation and deposition in tissue of amyloid fibrils.

Simulations of human lysozyme: probing the conformations triggering amyloidosis.

A natural mutant of human lysozyme, D67H, causes hereditary systemic nonneuropathic amyloidosis, which can be fatal. In this disease, insoluble beta-stranded fibrils (amyloids) are found in tissues stemming from the aggregation of partially folded intermediates of the mutant. In this study, we specifically compare the conformation and properties of the structures adopted from the induced unfolding, at elevated temperature, using molecular dynamics. To increase the sampling of the unfolding conformational landscape, three 5 ns trajectories are performed for each of the wild-type and mutant D67H proteins resulting in a total of 30 ns simulation. Our results show that the mutant unfolds slightly faster than the wild-type with both wild-type and mutant proteins losing most of their native secondary structure within the first 2 ns. They both develop random transient beta-strands across the whole polypeptide chain. Clustering analysis of all the conformations shows that a high population of the mutant protein conformations have a distorted beta-domain. This is consistent with experimental results suggesting that this region is pivotal in the formation of conformations prone to act as "seeds" for amyloid fiber formation.