At variance with A8-35, non-anionic amphipols (NAPols) can be used at low pH
(# 2018 by Francis Haraux)
4.2.3.3 NVoy ¼ NV10
A completely different non-ionic polymer, NVoy, also called NV10, has been used in two series of
experiments as a recipient during cell-free synthesis of MPs (Guild et al. 2011; Klammt et al. 2011; see
Chap. 7, § 7.3). NVoy is a commercial polymer, and neither its exact structure nor its synthesis appears
to have been published. A scheme available from its manufacturer’s web site is shown in Fig. 4.5B.
According to Klammt et al. (2011), “NVoy is a linear, uncharged molecule composed of a polyfructose
(25mer) backbone complemented with derivatized hydrophobic side chains with an overall molecular
weight of 5 kDa.” According to the same source, “static light scattering (SLS) coupled with refractive
index (RI) and SEC [measurements] revealed that this polymer forms stable micelle-like multimers of
approximately 112 kDa (22 polymer molecules) in aqueous solution.” Two of the GPCRs expressed in
the presence of NVoy were found to form small MP/NVoy complexes, as indicated by SEC and EM
data, and to bind specific ligands (Klammt et al. 2011). There is therefore good evidence that NVoy
qualifies as a non-ionic amphipol. Why it does, whereas “amphibiopols” (Duval-Terrié et al. 2003) do
not (Picard et al. 2004) is perhaps related to the different nature of the glycosidic backbone: very short
polyfructose, inulin-like chains (15 residues) in the case of NVoy (Klammt et al. 2011) and ~10Â
longer pullulan chains (~170 residues) in the case of “amphibiopols,” with a different branching of the
residues.
4.3
Self-Association Behavior of Amphipols in Aqueous Solutions
A prerequisite to the formation of small MP/polymer complexes is that the polymer does not form by
itself too large particles when solubilized in water. Indeed, in our experience, all polymer preparations
that self-organized into big particles were unable to form, once associated with MPs, the small objects
that are desirable for most biophysical studies. A good knowledge of the size, organization, and
dynamics of APol particles is important in many respects, be it to predict their behavior in separation
experiments or as a model to understanding the properties of MP-associated APols.
Upon being solubilized in water, amphiphilic polymers tend to self-organize and, more often
than not, to self-associate the hydrophobic effect pushing their hydrophobic moieties together, whereas
hydrophilic groups tend to disperse in water. Which structures are thus formed depends on the
distribution of the various groups along the polymer, two examples of which are shown in Fig. 4.9.
Most APols have the behavior shown to the left of the figure. Depending on the length of the polymer
4.3 Self-Association Behavior of Amphipols in Aqueous Solutions
169
(# 2018 by Francis Haraux)
4.2.3.3 NVoy ¼ NV10
A completely different non-ionic polymer, NVoy, also called NV10, has been used in two series of
experiments as a recipient during cell-free synthesis of MPs (Guild et al. 2011; Klammt et al. 2011; see
Chap. 7, § 7.3). NVoy is a commercial polymer, and neither its exact structure nor its synthesis appears
to have been published. A scheme available from its manufacturer’s web site is shown in Fig. 4.5B.
According to Klammt et al. (2011), “NVoy is a linear, uncharged molecule composed of a polyfructose
(25mer) backbone complemented with derivatized hydrophobic side chains with an overall molecular
weight of 5 kDa.” According to the same source, “static light scattering (SLS) coupled with refractive
index (RI) and SEC [measurements] revealed that this polymer forms stable micelle-like multimers of
approximately 112 kDa (22 polymer molecules) in aqueous solution.” Two of the GPCRs expressed in
the presence of NVoy were found to form small MP/NVoy complexes, as indicated by SEC and EM
data, and to bind specific ligands (Klammt et al. 2011). There is therefore good evidence that NVoy
qualifies as a non-ionic amphipol. Why it does, whereas “amphibiopols” (Duval-Terrié et al. 2003) do
not (Picard et al. 2004) is perhaps related to the different nature of the glycosidic backbone: very short
polyfructose, inulin-like chains (15 residues) in the case of NVoy (Klammt et al. 2011) and ~10Â
longer pullulan chains (~170 residues) in the case of “amphibiopols,” with a different branching of the
residues.
4.3
Self-Association Behavior of Amphipols in Aqueous Solutions
A prerequisite to the formation of small MP/polymer complexes is that the polymer does not form by
itself too large particles when solubilized in water. Indeed, in our experience, all polymer preparations
that self-organized into big particles were unable to form, once associated with MPs, the small objects
that are desirable for most biophysical studies. A good knowledge of the size, organization, and
dynamics of APol particles is important in many respects, be it to predict their behavior in separation
experiments or as a model to understanding the properties of MP-associated APols.
Upon being solubilized in water, amphiphilic polymers tend to self-organize and, more often
than not, to self-associate the hydrophobic effect pushing their hydrophobic moieties together, whereas
hydrophilic groups tend to disperse in water. Which structures are thus formed depends on the
distribution of the various groups along the polymer, two examples of which are shown in Fig. 4.9.
Most APols have the behavior shown to the left of the figure. Depending on the length of the polymer
4.3 Self-Association Behavior of Amphipols in Aqueous Solutions
169