Role of positions e and g in the fibrous assembly formation of an amphipathic α‐helix‐forming polypeptide

Abstract

We previously characterized α3, a polypeptide that has a three times repeated sequence of seven amino acids (abcdefg: LETLAKA) and forms fibrous assemblies composed of amphipathic α-helices. Upon comparison of the amino acid sequences of α3 with other α-helix forming polypeptides, we proposed that the fibrous assemblies were formed due to the alanine (Ala) residues at positions e and g. Here, we characterized seven α3 analog polypeptides with serine (Ser), glycine (Gly), or charged residues substituted for Ala at positions e and g. The α-helix forming abilities of the substituted polypeptides were less than that of α3. The polypeptides with amino acid substitutions at position g and the polypeptide KEα3, in which Ala was substituted with charged amino acids, formed few fibrous assemblies. In contrast, polypeptides with Ala replaced by Ser at position e formed β-sheets under several conditions. These results show that Ala residues at position e and particularly at position g are involved in the formation of fibrous assemblies.

Foreword to ‘Multiscale structural biology: biophysical principles and mechanisms underlying the action of bio-nanomachines’, a special issue in Honour of Fumio Arisaka’s 70th birthday

“…Within the phage-related area work on bacterial homologs of phage proteins (Uchida et al 2014), mechanistic action of the gp5 trimer in the cell puncturing device (Nishima et al 2011), and determination of the molecular architecture of the T4 phage neck region (Fokine et al 2013) (all reviewed in Arisaka and Kanamaru 2013). Further to this, being a Professor did not slow down Fumio's own experimental output, with his engagement in a range of collaborative projects on topics as diverse as receptor biology (Mio et al 2010), assembly of nanotechnology components (Yokoi et al 2010;Inaba et al 2012;Sanghamitra et al 2014), hemoglobin allostery (Arisaka et al 2011), crop protein analysis (Wadahama et al 2012;Sato et al 2015;Yamniuk et al 2015), autophagy (Araki et al 2013, amyloid analysis (Zhao et al 2016;Hall et al 2016), biopharmaceutical development (Iwura et al 2014a(Iwura et al , 2014b, AUC methodological development (Zhao et al 2015) and thermostable enzymes (Tamakoshi et al 2011;Chen et al 2011;Ozawa et al 2012) among many others (Huq et al 2010;Yamasaki et al 2010;Kanazawa et al 2010;Sawada et al 2011;Akita et al 2012;Nomura et al 2012;Ishii et al 2012;Nozawa et al 2013;Seio et al 2013;Takei et al 2014;Kumazaki et al 2014;Owa et al 2014;Iwura et al 2014aIwura et al ,...…”

pH responsiveness of fibrous assemblies of repeat‐sequence amphipathic α‐helix polypeptides

“…We designed polypeptide α3, which was composed of three repeats of the seven‐amino‐acid sequence abcdefg (LETLAKA) 3 . The hydrophobic surface of α3 consisted of leucine (Leu) and alanine (Ala), and the hydrophilic surface consisted of Glu, lysine (Lys), and threonine (Thr).…”

“…Almost all mutated polypeptides form fibrous assemblies under those buffer conditions in which an α‐helix is formed . The thinnest fibrous assemblies of α3 and of α3 analog polypeptides are about 20 Å wide; this width is in agreement with the width of one fiber of each bundle formed when the polypeptides form α‐helix associations …”

“…α‐helix formation ability of α3 depends on the polypeptide's concentration . Transmission electron microscopic observation has shown that α3 forms long fibrous assemblies .…”

“…Over the past 20 years, artificially designed α‐helix‐forming polypeptides have been reported to assemble into nanoscale fibrils . The formation of several types of fibrous assembly, as well as changes in the shape of these assemblies, is reportedly affected by the buffer conditions.…”