more speculatively, it is conceivable that one might harness the tendency to self-organization of APoldepleted MP/APol complexes to generate structures amenable to image analysis by EM (see Chap. 12,
§ 12.3.2).
Transferring MPs from detergent solutions to other APols than A8-35 or A8-75 is carried out
along similar ways (Table 5.3), but, except for OAPA-20 and PMAL-B (Nagy et al. 2001), the effects
of removing free APol have not been analyzed. They may well vary from one APol to the next, because
they are likely determined by the balance of forces between MP/APol, MP/MP, and APol/APol
interactions. One may perhaps expect, for instance, that MPs complexed by APols more highly
charged than A8-35, such as A8-75 or SAPols, will show less tendency to aggregate upon APol
depletion, whereas complexes with APols carrying no net charge, such as NAPols, might be more
prone to aggregation. This, however, is purely speculative and needs to be experimentally investigated.
Back transfer from APols to detergents or transfer to other surfactants such as other APols,
nanodiscs, lipid vesicles, or biological membranes is also possible and will be discussed in § 5.7.
Transfer from detergent solution is not the only way to form MP/APol complexes. As noted
above, alternative routes are (i) to directly extract MPs with APols; (ii) to transfer denatured MPs from
a denaturing solution to APols, where they will fold; and (iii) to synthesize the protein in vitro in the
presence of APol. The first approach has been validated mostly with styrene-maleic acid copolymers
(SMAs); the second with classical APols such as A8-35, SAPols, or NAPols; and the third with
uncharged APols, namely NAPols and NVoy (Table 5.3).
5.2.2
Direct Extraction of Proteins from Membranes
Direct extraction of MPs using APols has been mostly carried out with SMAs. As discussed in
§ 5.2.2.2, there are indications that certain MPs (or, perhaps more likely, proteins from certain
membranes) can be extracted using A8-35, but this line of research remains to be developed.
Direct extraction of membrane proteins by amphipols
(# 2018 by Francis Haraux)
5.2 Forming Membrane Protein/Amphipol Complexes
259
§ 12.3.2).
Transferring MPs from detergent solutions to other APols than A8-35 or A8-75 is carried out
along similar ways (Table 5.3), but, except for OAPA-20 and PMAL-B (Nagy et al. 2001), the effects
of removing free APol have not been analyzed. They may well vary from one APol to the next, because
they are likely determined by the balance of forces between MP/APol, MP/MP, and APol/APol
interactions. One may perhaps expect, for instance, that MPs complexed by APols more highly
charged than A8-35, such as A8-75 or SAPols, will show less tendency to aggregate upon APol
depletion, whereas complexes with APols carrying no net charge, such as NAPols, might be more
prone to aggregation. This, however, is purely speculative and needs to be experimentally investigated.
Back transfer from APols to detergents or transfer to other surfactants such as other APols,
nanodiscs, lipid vesicles, or biological membranes is also possible and will be discussed in § 5.7.
Transfer from detergent solution is not the only way to form MP/APol complexes. As noted
above, alternative routes are (i) to directly extract MPs with APols; (ii) to transfer denatured MPs from
a denaturing solution to APols, where they will fold; and (iii) to synthesize the protein in vitro in the
presence of APol. The first approach has been validated mostly with styrene-maleic acid copolymers
(SMAs); the second with classical APols such as A8-35, SAPols, or NAPols; and the third with
uncharged APols, namely NAPols and NVoy (Table 5.3).
5.2.2
Direct Extraction of Proteins from Membranes
Direct extraction of MPs using APols has been mostly carried out with SMAs. As discussed in
§ 5.2.2.2, there are indications that certain MPs (or, perhaps more likely, proteins from certain
membranes) can be extracted using A8-35, but this line of research remains to be developed.
Direct extraction of membrane proteins by amphipols
(# 2018 by Francis Haraux)
5.2 Forming Membrane Protein/Amphipol Complexes
259