A newly developed dilute magnesium alloy, Mg-0.27Al-0.13Ca-0.21Mn (at.%), shows extraordinary high-speed extrudabiliby of a die-exit speed of 60 m/min. Subsequent artificial aging at 200 °C (T5) enhanced the proof stress from 170 MPa to 207 MPa due to the precipitation of Guinier Preston (G.P.) zones and weakened basal texture while keeping good ductility of 12.5%. High-speed extrusion reduces the processing cost, so the dilute Mg-Al-Ca-Mn alloy could be a industrially viable low-cost medium strength structural material.

a b s t r a c tAs-cast Mg-0.27Al-0.13Ca-0.21Mn (at.%) alloy was extruded at temperatures from 350 C to 500 C. We examined the microstructural changes during extrusion at different temperatures to clarify dynamic recrystallization mechanisms during extrusion, and also investigated the effect of extrusion temperature on microstructures and mechanical properties of the alloy. High extrusion exit speed of 60 m/min was successfully achieved at wide range of temperatures from 350 C to 500 C even when as-cast dilute Mg-0.27Al-0.13Ca-0.21Mn (at.%) alloy was used as a billet for the extrusion. The extrusion at low temperature refines grain size and weakens basal texture due to continuous dynamic recrystallization (CDRX) together with double twinning. As a result, the alloy sample extruded at 350 C exhibits higher tensile proof stress of 206 MPa and higher tensile ductility of 29% than T5-treated 6063 aluminum alloy and commercial AZ31 magnesium alloy even in an as-extruded condition. Furthermore, HallePetch coefficient for compressive proof stress is 1.8 times larger than that for tensile one, resulting in improvement of yield stress anisotropy (compressive proof stress/tensile yield stress ratio).

Differential scanning calorimetry (DSC) indicated that PDZ3 undergoes a peculiar thermal denaturation exhibiting two endothermic peaks due to the formation of reversible oligomers at high temperature (N↔I 6 ↔D). This contrasts sharply with the standard 2-state denaturation model observed for small, globular proteins. We performed an alanine scanning analysis by individually mutating three hydrophobic residues at the crystallographic oligomeric interface (Phe340, Leu342, Ile389) and one away from the interface (Leu349, as a control). DSC analysis indicated that PDZ3-F340A and PDZ3-L342A exhibited a single endothermic peak. Furthermore, PDZ3-L342A underwent a perfect 2-state denaturation, as evidenced by the single endothermic peak, and confirmed by detailed DSC analysis, including global fitting of data measured at different protein concentrations. Reversible oligomerization (RO) at high temperatures by small globular proteins is a rare event. While we designed the mutations based on our previous study showing that a point mutation Val380 to a nonhydrophobic amino acid inhibited RO in DEN4 ED3, the results are nevertheless surprising since high-temperature RO involves proteins in a denatured state, as assessed by circular dichroism. Future studies will determine how and why mutations designed using crystal structures determined at ambient temperatures influence the formation of RO at high temperatures, and whether high-temperature ROs are related to the propensity of proteins to aggregate or precipitate at lower temperatures, which would provide a novel and unique way of controlling protein solubility and aggregation. Significance (120 words)Despite being a small globular protein, which normaly undergo a two-state unfolding, the thermal denaturation of PSD95-PDZ3, monitored by DSC, exhibited two

The third PDZ domain of the postsynaptic density protein 95 (PSD95‐PDZ3; 11 kDa, 103 residues) has a propensity to form amyloid fibrils at high temperatures. At neutral pH, PDZ3 is natively folded, but it exhibits a peculiar three‐state thermal unfolding with a reversible oligomerization (RO) equilibrium at high temperatures, which is uncharacteristic in the unfolding of a small globular protein as PDZ3 is. Here, we examined the RO's role in PDZ3's amyloidogenesis at high‐temperature using two variants (F340A and L342A) that suppress the high‐temperature RO and five single‐alanine‐mutated variants, where we mutated surface‐exposed hydrophobic residues to alanine. Circular Dichroism (CD), Analytical Ultracentrifuge (AUC), and other spectroscopic measurements confirmed the retention of the native structure at ambient temperature. Differential Scanning Calorimetry (DSC) was used to assess the presence or absence of the high‐temperature RO, and the amyloidogenicity of the variants was measured by Thioflavin T (ThT) fluorescence and Transmission Electron Microscopy (TEM). By comparing the fraction of RO and the ThT signal, we found that mutations that suppressed the high‐temperature RO strongly inhibited amyloidogenesis. On the other hand, all variants forming RO also formed amyloids under the same conditions as the wild‐type PDZ3.

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Abbreviations:PSD95: postsynaptic density-95 protein; PDZ3: the third PDZ domain from PSD95; Abstract (243 words)Differential scanning calorimetry (DSC) indicated that PDZ3 undergoes a peculiar thermal denaturation exhibiting two endothermic peaks due to the formation of reversible oligomers at high temperature (N↔I 6 ↔D). This contrasts sharply with the standard 2-state denaturation model observed for small, globular proteins. We performed an alanine scanning analysis by individually mutating three hydrophobic residues at the crystallographic oligomeric interface (Phe340, Leu342, Ile389) and one away from the interface (Leu349, as a control). DSC analysis indicated that PDZ3-F340A and PDZ3-L342A exhibited a single endothermic peak. Furthermore, PDZ3-L342A underwent a perfect 2-state denaturation, as evidenced by the single endothermic peak, and confirmed by detailed DSC analysis, including global fitting of data measured at different protein concentrations. Reversible oligomerization (RO) at high temperatures by small globular proteins is a rare event. While we designed the mutations based on our previous study showing that a point mutation Val380 to a nonhydrophobic amino acid inhibited RO in DEN4 ED3, the results are nevertheless surprising since high-temperature RO involves proteins in a denatured state, as assessed by circular dichroism. Future studies will determine how and why mutations designed using crystal structures determined at ambient temperatures influence the formation of RO at high temperatures, and whether high-temperature ROs are related to the propensity of proteins to aggregate or precipitate at lower temperatures, which would provide a novel and unique way of controlling protein solubility and aggregation. Significance (120 words)Despite being a small globular protein, which normaly undergo a two-state unfolding, the thermal denaturation of PSD95-PDZ3, monitored by DSC, exhibited two