The β-strand D of transthyretin trapped in two discrete conformations

• Published in: Biochimica et biophysica acta 2004-07, Vol.1700 (1), p.93-104
• Main Authors: Hörnberg, Andreas, Olofsson, Anders, Eneqvist, Therese, Lundgren, Erik, Sauer-Eriksson, A.Elisabeth
• Format: Article
• Language: English
• Subjects: Amyloid; Crystallography; Crystallography, X-Ray; Dimerization; Familial amyloidotic polyneuropathy; Humans; Hydrogen Bonding; Hydrogen-Ion Concentration; Models, Molecular; Molecular; Mutation; Mutation - genetics; Prealbumin; Prealbumin - chemistry; Prealbumin - genetics; Prealbumin - metabolism; Protein Conformation; Protein Denaturation; Transthyretin; Variant Ala108Tyr/Leu110Glu; X-Ray; X-ray structure
• ISSN: 1570-9639; 0006-3002; 1878-2434; 1878-1454
• DOI: 10.1016/j.bbapap.2004.04.004

Conformational changes in native and variant forms of the human plasma protein transthyretin (TTR) induce several types of amyloid diseases. Biochemical and structural studies have mapped the initiation site of amyloid formation onto residues at the outer C and D β-strands and their connecting loop. In this study, we characterise an engineered variant of transthyretin, Ala108Tyr/Leu110Glu, which is kinetically and thermodynamically more stable than wild-type transthyretin, and as a consequence less amyloidogenic. Crystal structures of the mutant were determined in two space groups, P2 12 12 and C2, from crystals grown in the same crystallisation set-up. The structures are identical with the exception for residues Leu55–Leu58, situated at β-strand D and the following DE loop. In particular, residues Leu55–His56 display large shifts in the C2 structure. There the direct hydrogen bonding between β-strands D and A has been disrupted and is absent, whereas the β-strand D is present in the P2 12 12 structure. This difference shows that from a mixture of metastable TTR molecules, only the molecules with an intact β-strand D are selected for crystal growth in space group P2 12 12. The packing of TTR molecules in the C2 crystal form and in the previously determined amyloid TTR (ATTR) Leu55Pro crystal structure is close-to-identical. This packing arrangement is therefore not unique in amyloidogenic mutants of TTR.