The induction of  -helical structure in partially unfolded HypF-N does not affect its aggregation propensity

Abstract

The conversion of proteins into structured fibrillar aggregates is a central problem in protein chemistry, biotechnology, biology and medicine. It is generally accepted that aggregation takes place from partially structured states of proteins. However, the role of the residual structure present in such conformational states is not yet understood. In particular, it is not yet clear as to whether the α-helical structure represents a productive or counteracting structural element for protein aggregation. We have addressed this issue by studying the aggregation of pH-unfolded HypF-N. It has previously been shown that the two native α-helices of HypF-N retain a partial α-helical structure in the pH-unfolded state and that these regions are also involved in the formation of the cross-β structure of the aggregates. We have introduced mutations in such stretches of the sequence, with the aim of increasing the α-helical structure in the key regions of the pH-unfolded state, while minimizing the changes of other factors known to influence protein aggregation, such as hydrophobicity, β-Sheet propensity, etc. The resulting HypF-N mutants have higher contents of α-helical structure at the site(s) of mutation in their pH-unfolded states, but such an increase does not correlate with a change of aggregation rate. The results suggest that stabilisation of α-helical structure in amyloidogenic regions of the sequence of highly dynamic states does not have remarkable effects on the rate of protein aggregation from such conformational states. Comparison with other protein systems indicate that the effect of increasing α-helical propensity can vary if the stabilised helices are in non-amyloidogenic stretches of initially unstructured peptides (accelerating effect), in amyloidogenic stretches of initially unstructured peptides (no effect) or in amyloidogenic stretches of initially stable helices (decelerating effect).

Unfolding of CPR3 Gets Initiated at the Active Site and Proceeds via Two Intermediates

“…6 A), it appears that they are amyloidlike oligomers. Similar spherical oligomers have been observed in many other systems (41)(42)(43). We also analyzed the secondary structural status of the two aggregates by far-UV CD (Fig.…”

Nucleophosmin contains amyloidogenic regions that are able to form toxic aggregates under physiological conditions

“…Collectively, these considerations indicate that the residual interactions involving H2 and stabilizing its α‐helical structure in the NPM1‐CTD denatured state prevent amyloidlike aggregation. It has been shown that the stabilization of the α‐helical structure can cause an acceleration of the aggregation process, depending on the initial stability and location of the α‐helices (51). In particular, the effect can vary if the stabilized helices are 1 ) in nonamyloidogenic stretches of initially unstructured peptides (accelerating effect), 2 ) in amyloidogenic stretches of initially unstructured peptides (no effect), or 3 ) in amyloidogenic stretches of initially stable helices (decelerating effect).…”

Urea titration of a lipase from Pseudomonas sp. reveals four different conformational states, with a stable partially folded state explaining its high aggregation propensity

“…Moroever, when a key region of the sequence that plays a crucial role in amyloid formation adopts stable α-helical structure, this type of secondary structure is protective against aggregation and its further stabilization by mutations counteracts amyloid aggregation [44][45][46][47][48]. However, it can be aggregation-promoting for nonamyloidogenic initially unstructured stretches [49]. This seems to be the case also for lipase, as the F171E mutation within the most important aggregation promoting region (residues 160-172) inhibits aggregation significantly, due to its ability to decrease and increase the β-sheet and α-helical propensities, respectively [9].…”