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The influence of poly(ethylene glycol) on the micelle formation of alkyl maltosides used in membrane protein crystallization
Müh, Frank; DiFiore, Dörte; Zouni, Athina
With the aim of better understanding the phase behavior of alkyl maltosides (n-alkyl-beta-D-maltosides, C(n)G(2)) under the conditions of membrane protein crystallization, we studied the influence of poly(ethylene glycol) (PEG) 2000, a commonly used precipitating agent, on the critical micelle concentration (CMC) of the alkyl maltosides by systematic variation of the number n of carbon atoms in the alkyl chain (n = 10, 11, and 12) and the concentration of PEG2000 (chi) in a buffer suitable for the crystallization of cyanobacterial photosystem II. CMC measurements were based on established fluorescence techniques using pyrene and 8-anilinonaphthalene-1-sulfonate (ANS). We found an increase of the CMC with increasing PEG concentration according to ln(CMC/CMC0) = k(P)chi, where CMC0 is the CMC in the absence of PEG and k(P) is a constant that we termed the "polymer constant". In parallel, we measured the influence of PEG2000 on the surface tension of detergent-free buffer solutions. At PEG concentrations chi > 1% w/v, the surface pressure pi(s)(chi) = gamma(0) - gamma(chi) was found to depend linearly on the PEG concentration according to pi(s)(chi) = kappa chi + pi(s)(0), where gamma(0) is the surface tension in the absence of PEG. Based on a molecular thermodynamic modeling, CMC shifts and surface pressure due to PEG are related, and it is shown that k(P) = kappa c(n) + eta, where c(n) is a detergent-specific constant depending inter alia on the alkyl chain length n and eta is a correction for molarity. Thus, knowledge of the surface pressure in the absence of a detergent allows for the prediction of the CMC shift. The PEG effect on the CMC is discussed concerning its molecular origin and its implications for membrane protein solubilization and crystallization.
- Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.
- This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.
