International
Tables for
Crystallography
Volume F
Crystallography of biological macromolecules
Edited by E. Arnold, D. M. Himmel and M. G. Rossmann

International Tables for Crystallography (2012). Vol. F, ch. 4.2, pp. 122-123   | 1 | 2 |

Section 4.2.2. Principles of membrane-protein crystallization

H. Michela*

aMax-Planck-Institut für Biophysik, Heinrich-Hoffmann-Strasse 7, D-60528 Frankfurt/Main, Germany
Correspondence e-mail: michel@mpibp-frankfurt.mpg.de

4.2.2. Principles of membrane-protein crystallization

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There are two principal types of membrane-protein crystals (Michel, 1983[link]). First, one can think of forming two-dimensional crystals in the planes of the membrane and stacking these two-dimensional crystals in an ordered way with respect to up and down orientation, rotation and translation. This membrane-protein crystal type (`type I') is attractive, because it contains the membrane proteins in their native environment. It should even be possible to study lipid–protein interactions. Crystals of bacteriorhodopsin of this type have been obtained either upon slow removal of the detergent by dialysis at high ionic strength (Henderson & Shotton, 1980[link]), or by a novel approach using lipidic bicontinuous cubic phases (Landau & Rosenbusch, 1996[link]; Pebay-Peyroula et al., 1997[link]; see also below). Alternatively, one can try to crystallize the membrane protein with the detergents still bound in a micellar manner. These crystals are held together via polar interactions between the polar surfaces of the membrane proteins. The detergent plays a more passive, but still critical, role. Such `type II' crystals look very much like crystals of soluble globular proteins. The same crystallization methods and equipment as for soluble globular proteins (see Chapter 4.1[link] ) can be used. However, the use of hanging drops is sometimes difficult, because the presence of detergents leads to a lower surface tension of the protein solution. Intermediate forms between type I and type II crystals are feasible, e.g. by fusion of detergent micelles.

The use of detergent concentrations just above the CMC of the respective detergent is recommended in order to prevent complications caused by pure detergent micelles. Unfortunately, the CMC is not constant. Normally, the CMC provided by the vendor has been determined in water at room temperature. A compilation of potentially useful detergents, their CMCs and their molecular weights is presented in Table 4.2.2.1[link]. The CMC is generally lower at high ionic strength and at high temperatures. The presence of glycerol and similar compounds, as well as that of chaotropic agents (Midura & Yanagishita, 1995[link]), also influences (decreases) the CMC.

Table 4.2.2.1| top | pdf |
Potentially useful detergents for membrane-protein crystallizations with molecular weights and CMCs [in water, from Michel (1991) or as provided by the vendor]

The lengths of the alkyl or alkanoyl side chains are given as [\hbox{C}_{6}] to [\hbox{C}_{16}].

DetergentMolecular weightCMC (mM)
Alkyl dihydroxypropyl sulfoxide    
C8 238 20.6
N,N-Dimethylalkylamine-N-oxides    
C8 173 162
C9 187 50
C10 201 20
C12 229 1–2
n-Dodecyl-N,N-dimethylglycine (zwitterionic) 271 1.5
N-Alkyl-β-D-glucopyranosides    
C6 264 250
C7 278 79
C8 292 30
C9 306 6.5
C10 320 2.6
n-Alkanoyl-N-hydroxyethylglucamides (`HEGA-n')    
C8 351 109
C9 365 39
C10 379 7.0
C11 393 1.4
Alkyl hydroxyethyl sulfoxide    
C8 222 15.8
n-Alkyl-β-D-maltosides    
C6 426 210
C8 454 19.5
C9 468 6
C10 483 1.8
C11 497 0.6
C12 511 0.17
C13 525 0.033
C14 539 0.01
C16 567 0.006
cyclohexyl-C1 438 340
cyclohexyl-C2 452 120
cyclohexyl-C3 466 34.5
cyclohexyl-C4 480 7.6
cyclohexyl-C5 494 2.4
cyclohexyl-C6 508 0.56
cyclohexyl-C7 522 0.19
n-Alkanoyl-N-methylglucamides (`MEGA-n')    
C8 321 79
C9 335 25
C10 349 6
Methyl-6-O-(N-heptylcarbamoyl)-α-D-glucopyranoside (`HECAMEG') 335 19.5
n-Alkylphosphocholines (zwitterionic)    
C8 295 114
C9 309 39.5
C10 323 11
C12 315 1.5
C14 379 0.12
C16 407 0.013
Polyoxyethylene monoalkylethers (CnEm)    
C8E4 306 7.9
C8E5 350 7.1
C10E6 422 0.9
C12E8 538 0.071
n-Alkanoylsucrose    
C10 497 2.5
C12 525 0.3
n-Alkyl-β-D-thioglucopyranosides    
C7 294 29
C8 308 9
C9 322 2.9
C10 336 0.9
n-Alkyl-β-D-thiomaltopyranosides    
C8 471 8.5
C9 485 3.2
C10 499 0.9
C11 513 0.21
C12 527 0.05

References

Henderson, R. & Shotton, D. (1980). Crystallization of purple membrane in three dimensions. J. Mol. Biol. 139, 99–109.
Landau, E. M. & Rosenbusch, J. P. (1996). Lipidic cubic phases: a novel concept for the crystallization of membrane proteins. Proc. Natl Acad. Sci. USA, 93, 14532–14535.
Michel, H. (1983). Crystallization of membrane proteins. Trends Biochem. Sci. 8, 56–59.
Midura, R. J. & Yanagishita, M. (1995). Chaotropic solvents increase the critical micellar concentrations of detergents. Anal. Biochem. 228, 318–322.
Pebay-Peyroula, E., Rummel, G., Rosenbusch, J. P. & Landau, E. M. (1997). X-ray structure of bacteriorhodopsin at 2.5 Å from microcrystals grown in lipidic cubic phases. Science, 277, 1676–1681.








































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