exhibited subnanomolar affinities and showed selectivity for Zn over other divalent
cations [108].
In summary, a number of crucial tertiary structure motifs have been already
realized using peptoids. The final hierarchical level in proteins is the quaternary
structure, which will be discussed in the following section.
5 Quaternary Structure Mimetics and Self-Assembly
of Peptoids
The previous sections described concepts and structures for realizing secondary and
tertiary structure using peptoids. In this, relatively little overlap could be identified
with traditional polymer chemistry and self-assembly.
The subject of this section is the self-assembly of different peptoid (macro-)
molecules, something which could be also termed the quaternary structure. We are
aware that for structural biologists, quaternary structure is a more or less exactly
defined supramolecular assembly of multiple folded proteins. We shall not be so
strict, if only to leave room for creativity in what might be accomplished with
peptoids in the future. In this section, we will discuss briefly supramolecular
structures that have been reported using peptoids. Naturally, this is a field much
closer to the heart of the polymer chemist.
5.1 Sheets
Sheets, in particular β-sheets, are part of the tertiary structure of proteins. However,
to the best of our knowledge, such sheets that comprise only one individual peptoid
chain have not been reported to date.
Zuckerman and coworkers have prepared polypeptoids (36-mers), in which
anionic or cationic (A) and hydrophobic (B) monomer units alternate in different
patterns (AB, ABB, and ABBB). When two such peptoids of the same architecture
but opposite charge were mixed, globular aggregates formed. However, within
several hours, large but ultrathin sheets of 2.7 nm thickness formed in high yields
(Fig. 12) [109]. The peptoid chains were highly extended, as evidenced by
aberration-corrected transmission electron microscopy. Extraordinarily large
aspect ratios and the exceedingly simple preparation of these sheets by simple
mixing of appropriate peptoids are highlights of this approach [110]. Similar sheets
are also possible from a single peptoid [111]. The cationic and anionic moieties
could be either incorporated in an alternating or block-like manner as long as the
hydrophobic and ionic moieties were alternating. Because the aggregation is
dependent on electrostatic and hydrophobic interactions, the sheet formation was
pH dependent and organic solvents could perturb the hydrophobic interactions,
destroying the aggregates.
406
N. Gangloff and R. Luxenhofer
cations [108].
In summary, a number of crucial tertiary structure motifs have been already
realized using peptoids. The final hierarchical level in proteins is the quaternary
structure, which will be discussed in the following section.
5 Quaternary Structure Mimetics and Self-Assembly
of Peptoids
The previous sections described concepts and structures for realizing secondary and
tertiary structure using peptoids. In this, relatively little overlap could be identified
with traditional polymer chemistry and self-assembly.
The subject of this section is the self-assembly of different peptoid (macro-)
molecules, something which could be also termed the quaternary structure. We are
aware that for structural biologists, quaternary structure is a more or less exactly
defined supramolecular assembly of multiple folded proteins. We shall not be so
strict, if only to leave room for creativity in what might be accomplished with
peptoids in the future. In this section, we will discuss briefly supramolecular
structures that have been reported using peptoids. Naturally, this is a field much
closer to the heart of the polymer chemist.
5.1 Sheets
Sheets, in particular β-sheets, are part of the tertiary structure of proteins. However,
to the best of our knowledge, such sheets that comprise only one individual peptoid
chain have not been reported to date.
Zuckerman and coworkers have prepared polypeptoids (36-mers), in which
anionic or cationic (A) and hydrophobic (B) monomer units alternate in different
patterns (AB, ABB, and ABBB). When two such peptoids of the same architecture
but opposite charge were mixed, globular aggregates formed. However, within
several hours, large but ultrathin sheets of 2.7 nm thickness formed in high yields
(Fig. 12) [109]. The peptoid chains were highly extended, as evidenced by
aberration-corrected transmission electron microscopy. Extraordinarily large
aspect ratios and the exceedingly simple preparation of these sheets by simple
mixing of appropriate peptoids are highlights of this approach [110]. Similar sheets
are also possible from a single peptoid [111]. The cationic and anionic moieties
could be either incorporated in an alternating or block-like manner as long as the
hydrophobic and ionic moieties were alternating. Because the aggregation is
dependent on electrostatic and hydrophobic interactions, the sheet formation was
pH dependent and organic solvents could perturb the hydrophobic interactions,
destroying the aggregates.
406
N. Gangloff and R. Luxenhofer