vs. MP/DDM complexes, but the most reliable data seem to point to MP/A8-35 complexes being
smaller than MP/DDM ones. Some elements of discussion are provided in Box 5.2.
Box 5.2 Are Membrane Protein/A8-35 Complexes Actually Bigger Than Membrane
Protein/Dodecylmaltoside Ones?
There is a seeming paradox in the fact that most comparisons of the composition of MP/A8-35
vs. MP/DDM complexes indicate that a given protein binds less APol than detergent (Table 5.5 and
Fig. 5.13), whereas a couple of estimates of the size of the two types of complexes conclude that the
former are bigger than the latter. Historically, the first comparison was carried out using as a model
the sarcoplasmic Ca
2+ -ATPase, SERCA1a (Champeil et al. 2000; Fig. 5.18). Experimental
conditions were not ideal, because it had not been realized, at the time, that artifactual grafting of
dicyclohexylurea increased the hydrophobicity of certain A8-35 batches, leading MP/APol
complexes to form small oligomers (Gohon et al. 2004, 2006), nor that traces of Ca
2+ caused the
complexes to aggregate (Picard et al. 2006; see Chap. 4, § 4.3.1.2.1). Nevertheless, the data did
suggest that SERCA1a/A8-35 complexes are bigger than SERCA1a/DDM ones (Fig. 5.18).
This conclusion, however, was invalidated when the comparison of R S values obtained for
BR/A8-35 complexes by SEC, SANS, and AUC showed that SEC grossly overestimates the R S of
Fig. 5.19 3D maps of SoPIP2;1 tetramers complexed by (A) OG, (B) DDM, (C)
LMNG, and (D) A8-35. Isocontours include overall masses of 190 kDa (A),
220 kDa (B), 280 kDa (C), and 340 kDa (D). The scale bar represents 20 Å
(From Vahedi-Faridi et al. 2013).
Fig. 5.18 Size exclusion chromatography of SERCA1a either trapped with A8-35
or solubilized in DDM. Solid thick line, chromatography in the absence of detergent
of delipidated SERCA1a/A8-35 complexes; dashed thick line, chromatography in
the presence of 1 gÁL
À1 DDM of a delipidated SERCA1a/DDM complex without
amphipol. The thin lines correspond to gel filtration standard proteins, eluted in the
absence or presence of detergent (This research was originally published in Champeil
et al. 2000, # The American Society for Biochemistry and Molecular Biology).
5.3 Composition, Organization, Dynamics, and Solution Properties of Membrane. . .
281
smaller than MP/DDM ones. Some elements of discussion are provided in Box 5.2.
Box 5.2 Are Membrane Protein/A8-35 Complexes Actually Bigger Than Membrane
Protein/Dodecylmaltoside Ones?
There is a seeming paradox in the fact that most comparisons of the composition of MP/A8-35
vs. MP/DDM complexes indicate that a given protein binds less APol than detergent (Table 5.5 and
Fig. 5.13), whereas a couple of estimates of the size of the two types of complexes conclude that the
former are bigger than the latter. Historically, the first comparison was carried out using as a model
the sarcoplasmic Ca
2+ -ATPase, SERCA1a (Champeil et al. 2000; Fig. 5.18). Experimental
conditions were not ideal, because it had not been realized, at the time, that artifactual grafting of
dicyclohexylurea increased the hydrophobicity of certain A8-35 batches, leading MP/APol
complexes to form small oligomers (Gohon et al. 2004, 2006), nor that traces of Ca
2+ caused the
complexes to aggregate (Picard et al. 2006; see Chap. 4, § 4.3.1.2.1). Nevertheless, the data did
suggest that SERCA1a/A8-35 complexes are bigger than SERCA1a/DDM ones (Fig. 5.18).
This conclusion, however, was invalidated when the comparison of R S values obtained for
BR/A8-35 complexes by SEC, SANS, and AUC showed that SEC grossly overestimates the R S of
Fig. 5.19 3D maps of SoPIP2;1 tetramers complexed by (A) OG, (B) DDM, (C)
LMNG, and (D) A8-35. Isocontours include overall masses of 190 kDa (A),
220 kDa (B), 280 kDa (C), and 340 kDa (D). The scale bar represents 20 Å
(From Vahedi-Faridi et al. 2013).
Fig. 5.18 Size exclusion chromatography of SERCA1a either trapped with A8-35
or solubilized in DDM. Solid thick line, chromatography in the absence of detergent
of delipidated SERCA1a/A8-35 complexes; dashed thick line, chromatography in
the presence of 1 gÁL
À1 DDM of a delipidated SERCA1a/DDM complex without
amphipol. The thin lines correspond to gel filtration standard proteins, eluted in the
absence or presence of detergent (This research was originally published in Champeil
et al. 2000, # The American Society for Biochemistry and Molecular Biology).
5.3 Composition, Organization, Dynamics, and Solution Properties of Membrane. . .
281