The fibrillogenic L178H variant of apolipoprotein A-I forms helical fibrils

Abstract

A number of amyloidogenic variants of apoA-I have been discovered but most have not been analyzed. Previously, we showed that the G26R mutation of apoA-I leads to increased β-strand structure, increased N-terminal protease susceptibility, and increased fibril formation after several days of incubation. In vivo, this and other variants mutated in the N-terminal domain (residues 26 to ∼90) lead to renal and hepatic accumulation. In contrast, several mutations identified within residues 170 to 178 lead to cardiac, laryngeal, and cutaneous protein deposition. Here, we describe the structural changes in the fibrillogenic variant L178H. Like G26R, the initial structure of the protein exhibits altered tertiary conformation relative to wild-type protein along with decreased stability and an altered lipid binding profile. However, in contrast to G26R, L178H undergoes an increase in helical structure upon incubation at 37°C with a half time (t1/2) of about 12 days. Upon prolonged incubation, the L178H mutant forms fibrils of a diameter of 10 nm that ranges in length from 30 to 120 nm. These results show that apoA-I, known for its dynamic properties, has the ability to form multiple fibrillar conformations, which may play a role in the tissue-specific deposition of the individual variants.

Dual Role of an N-terminal Amyloidogenic Mutation in Apolipoprotein A-I

“…We also found that the amyloid fibrils of the 1-83 fragments exhibit strong toxicity to HEK293 cells as with amyloid ␤ fibrils (40). To our knowledge, the finding that the 1-83 fragment of apoA-I forms amyloid fibrils at physiological neutral pH is quite novel because the previous observations indicated that the fibril formation of apoA-I in vitro requires the acidic condition (16,41,42), methionine oxidation (19), or amyloidogenic mutations (23,43).…”

“…In fact, our recent hydrogen-deuterium exchange and mass spectroscopy measurements of apoA-I Iowa demonstrated that the G26R mutation induces widespread structural reorganization of residues in the central region of the apoA-I molecule despite a small change in the net helical contents (47). Similarly to the G26R mutation, the fibrillogenic L178H mutation, which is also located within the N-terminal helix bundle, was shown to exhibit a decreased protein stability and an altered lipid binding profile (43). In addition, oxidation of the methionine residues of apoA-I causes the destabilization of the tertiary and quaternary structure of the protein, leading to the formation of amyloid fibrils (19).…”

Dual Actions of Apolipoprotein A-I on Glucose-Stimulated Insulin Secretion and Insulin-Independent Peripheral Tissue Glucose Uptake Lead to Increased Heart and Skeletal Muscle Glucose Disposal

“…Expression and Purification of Recombinant Human ApoA-I Human apoA-I containing a His tag at the N terminus was expressed in bacteria and purified using immobilized metal affinity chromatography followed by tobacco etch virus protease treatment to remove the His tag, as previously described (10,11). ApoA-I proteins were produced either in-house or at the Lund University Protein Production Platform (LP3).…”

Elucidation of the Aggregation Pathways of Helix–Turn–Helix Peptides: Stabilization at the Turn Region Is Critical for Fibril Formation

“…More recently, the apo A-I variant L178H has been shown to form fibrils with exclusively α-helical structure. 25 The L178H variant is the first report of a full-length variant of apo A-I that forms α-helical fibrils. The presence of α-helical character in physiological apo A-I fibrils indicates that this secondary structure is important in protein aggregation and disease, and suggests that our work on apo A-I mimetic peptides may inform this growing area of exploration.…”