A β/γ Motif to Mimic α‐Helical Turns in Proteins

β- and γ-Amino Acids at α-Helical Interfaces: Toward the Formation of Highly Stable Foldameric Coiled Coils

“…These studies revealed that no particular helix orientation is preferred in either of the two investigated bundles, even though we intended to impose antiparallel coiled-coil formation by immobilizing B3β2γ Cterminally during the phage display screen. However, considering the absence of charged side chains in the randomized positions that could enforce directionality, the formation of both parallel and antiparallel bundles, as observed with the parental system, 19 is not surprising.…”

“…19 Aiming to stabilize this chimeric system, denoted Acid-pp/B3β2γ, we recently utilized a phage display screen to isolate optimal all-α binding partners for the chimeric peptide. 20 This screen led to the selection of Acid-pp variants containing a cysteine that significantly improves coiled-coil core packing through the formation of an interhelical S−H···OC H-bond with a non-H-bonded backbone carbonyl of the αβγ-chimera.…”

“…We assumed that the C-terminal immobilization of B3β2γ would lead to the isolation of different and perhaps even more thermally stable complexes based on noncovalent interactions under an antiparallel coiled coil regime. Therefore, B3β2γ was immobilized on streptavidin coated magnetic particles via a Cterminally attached biotin and the four central heptad positions of the Acid-pp α-peptide that directly interact with the βγ-segment of the chimeric B3β2γ peptide (a' 15 , d′ 18 , e′ 19 , and g′ 21 ) were randomized. After six rounds of panning, four sequences were isolated (Figure 1).…”

“…20,21 One of these two new sequences bears leucine in all four randomized positions (denoted Acid-LLLL). Likewise, a second peptide (Acid-LFYL) contains hydrophobic amino acids in three of the randomized positions; however, polar tyrosine occupies position e′ 19 . The remaining two sequences harbor charged amino acids in most of the randomized positions.…”

“…However, similar to our previous result obtained in a parallel regime, 20 cysteine is found in the remaining hydrophobic core position d′ 18 . The presence of another polar residue at position g′ 21 in combination with the rather small hydrophobic alanine at position e′ 19 indicates that this assembly is stabilized by electrostatic interactions rather than being a consequence of the hydrophobic effect. Given the diversity within the selection outcome, these results differ substantially from our former screen under a parallel coiled-coil regime from which two highly similar sequences containing a cysteine in combination with a bulky hydrophobic residue in randomized positions emerged.…”