Gelsolin-related amyloidosis. Identification of the amyloid protein in Finnish hereditary amyloidosis as a fragment of variant gelsolin.

Abstract

The Finnish type of familial amyloidosis is a systemic disease characterized by progressive cranial neuropathy, corneal lattice dystrophy, and distal sensimotor neuropathy. Amyloid fibrils were isolated from the kidney and heart of a patient with Finnish amyloidosis. After solubilization, the amyloid proteins were fractionated by gel filtration and purified by reverse-phase HPLC. Complete amino acid sequence analyses show that the two amyloid components obtained are fragments of gelsolin, an actin-modulating protein occurring in plasma and the cytoskeleton. The larger component represents residues 173-243 and the minor component residues 173-225, respectively, of mature gelsolin. When compared with the predicted primary structure of human gelsolin a single amino acid substitution is present in amyloid: at position 15 of the amyloid proteins an asparagine is found instead of an aspartic acid residue at the corresponding position (187)

Ca 2+ binding by domain 2 plays a critical role in the activation and stabilization of gelsolin

“…In this heritable disease, Asp-187, which is part of the G2 Ca-coordination sphere, is mutated to Asn or Tyr (20). The mutant proteins are unable to bind Ca 2ϩ at this site and can be predicted to have three abnormalities with regard to Cadependent activation.…”

“…The second, to the activated state, occurs at Ϸ10 M to 1 mM Ca 2ϩ (17)(18)(19). A single mutation within the type 2 metal ion-binding site in G2-of Asp-187 to Asn or Tyr-is the cause of familial amyloidosis Finnish-type (FAF), characterized by the extracellular deposition of a 71-residue fragment of gelsolin (20). It has been proposed that this mutation destabilizes gelsolin through loss of Ca coordination at the type 2 site in G2 (10), making it susceptible to cleavage by furin in the acidic trans-Golgi compartment (21).…”

“…It has been proposed that this mutation destabilizes gelsolin through loss of Ca coordination at the type 2 site in G2 (10), making it susceptible to cleavage by furin in the acidic trans-Golgi compartment (21). The resulting 68-kDa fragment is further cleaved by membrane-associated type I matrix metalloproteases located proximal to the extracellular matrix (22) into 8-and 5-kDa fragments, Ala-173-Met-243 and Ala-173-Arg-225, respectively, which form the deposits (20,23). Aggregation assays demonstrate that wild-type gelsolin Ala-173-Met-243 is as amyloidogenic as the corresponding fragment containing the Asp187Asn mutation and is more amyloidogenic than the one containing the Asp187Tyr mutation.…”

Amyloidogenesis of Natively Unfolded Proteins

“…The mutations (D187N/Y) causing gelsolin amyloidosis disrupts Ca 2+ binding within domain 2 which makes it susceptible to aberrant cleavage by furin yielding a secreted 68 kDa fragment referred to as C68 [319,320]. The C68 fragment is further cleaved in at least two positions by metalloprotease(s) producing 8 (residues A173-M243) and 5 kDa (residues A173-R225) gelsolin fragments which compose the amyloid deposits in patients [321,322]. Far-UV CD analysis of the amyloidogenic A173-M243 fragment of the D187N gelsolin revealed that this protein being substantially unfolded possesses structural features typical of the pre-molten globule [323].…”

Apolipoprotein AI mutation Arg-60 causes autosomal dominant amyloidosis.

“…In the rare Finnish type of FAP, a variant of gelsolin (3) has been identified; and in FAP of the Iowa type, a variant of apolipoprotein AI (apoAI) (4,5), the major apolipoprotein of high density lipoprotein (HDL) (6), has been reported. The apoAl Iowa variant protein, with arginine substituted for glycine at position 26, has also been found postmortem in a single patient with non-neuropathic hereditary systemic amyloidosis (7).…”