ANALYSIS OF X-RAY-DIFFRACTION PATTERNS FROM AMYLOID OF BIOPSIED VITREOUS-HUMOR AND KIDNEY OF TRANSTHYRETIN (TTR) MET30 FAMILIAL AMYLOIDOTICPOLYNEUROPATHY (FAP) PATIENTS - AXIALLY ARRAYED TTR MONOMERS CONSTITUTE THE PROTOFILAMENT

Familial amyloidotic polyneuropathy (FAP) is characterized by deposits of amyloid fibers in which the major protein component is transthyret in (TTR). Nearly fifty mutations have been reported for the TTR in her editary FAP. Protein crystallography of mutant TTRs has shown that the molecular structures of the variant molecules are similar to those fo und in the wild type. On this basis, the FAP fibers were initially pro posed to consist of native-like TTR tetramers. In the current paper, w e used x-ray fiber diffraction to study the structure of FAP fibers fr om biopsy samples of vitreous humor and kidney. The reflections of the vitreous sample showed a cross-beta diffraction pattern. All the meri dional reflections were indexed by a one-dimensional, 29 Angstrom-peri od lattice, and the equatorial reflections were indexed by an apparent one-dimensional 67 Angstrom-period lattice. The x-ray intensity distr ibution indicated that the unit structure, which is similar to a TTR m onomer, is composed of a pair of beta-sheets consisting of four hydrog en-bonded beta-chains per sheer, with the beta-chains oriented approxi mately normal to the fiber axis. The axial disposition of these units, with a 29 Angstrom-period, constitutes the protofilament; and a tetra meric lateral assembly of the protofilaments containing the core domai n of the similar to 20 Angstrom-wide beta-sheet structure constitutes the FAP amyloid fiber. An inter-fiber separation of 75 Angstrom in the se concentrated samples accounts or the apparent one-dimensional latti ce perpendicular to the fiber axis. In the delipidated kidney FAP samp le, the diffraction pattern indicated a pair of beta-sheets, suggestin g that the protofilament structure in kidney is similar to that in vit reous humor. In the non-delipidated sample the successive sharp reflec tions indexed to a one-dimensional, 48.9 Angstrom-lattice, and the ele ctron density projection showed a density elevation at the center of a lipid bilayer. This suggests that lipid may be associated with the mo nomeric TTR in the kidney FAP protofilament.