Destabilization of Ca2+-free gelsolin may not be responsible for proteolysis in Familial Amyloidosis of Finnish Type

Mutations at position 187 in secreted gelsolin enable aberrant proteolysis at the 172-173 and 243-244 amide bonds, affording the 71-residue amyloidoge nic peptide deposited in Familial Amyloidosis of Finnish Type (FAF), Thermo dynamic comparisons of two different domain 2 constructs were carried out t o study possible effects of the mutations on proteolytic susceptibility. In the construct we consider to be most representative of domain 2 in the con text of the full-length protein (134-266), the D187N FAF variant is slightl y destabilized relative to wild type (WT) under the conditions of urea dena turation, but exhibits a T-m identical to WT. The D187Y variant is less sta ble to intermediate urea concentrations and exhibits a T-m that is estimate d to be approximate to5 degreesC lower than WT (pH 7.4, Ca2+-free). Althoug h the thermodynamic data indicate that the FAF mutations may slightly desta bilize domain 2, these changes are probably not sufficient to shift the nat ive to denatured state equilibrium enough to enable the proteolysis leading to FAF, Biophysical data indicate that these two FAF variants may have dif ferent native state structures and possibly different pathways of amyloidos is.