Effect of detergent alkyl chain length on crystallization of a detergent-solubilized membrane protein: correlation of protein-detergent particle sizeand particle-particle interaction with crystallization of the photosynthetic reaction center from Rhodobacter sphaeroides

The effect of detergent alkyl chain length on the crystallization of deterg ent-solubilized membrane proteins was characterized using the reaction cent er (RC) from Rhodobacter sphaeroides as a model. Crystallization was perfor med in the presence of both n-alkyl-beta-D-glucopyranosides, C(n)G, where t he alkyl chain length, n, was varied from 8 to 10, and dodecyl-dimethylamin e-N-oxide (C(12)DAO). A pronounced effect of detergent chain length was fou nd on the ability to crystallize the reaction center. Small-angle neutron s cattering measurements (SANS) demonstrated that the variation in the abilit y to crystallize the reaction center is correlated with changes in the appa rent radius of gyration, R-g, of the reaction center-detergent particle, re flecting changes in the size of the reaction center and strength of the int er-particle interactions. Specifically, reaction center crystallization in the absence of additional amphiphiles was found to occur only with octylglu coside, C(8)G. Crystallization in the presence of longer chain detergents, C(9)G, C(10)G, C(12)DAO, required the use of an additional small amphiphile , heptanetriol (HT). SANS measurements showed that the apparent R-g of the reaction center-detergent particle increased with increasing detergent chai n length, and that the addition of HT reduces his parameter. The addition o f HT was found to impede crystallization in the presence of C(8)G. This inh ibition could be reversed by increasing C(8)G concentration with respect to HT, resulting in the formation of alternate crystal forms. Taken together, these results suggest that detergents and small molecule amphiphiles used in membrane protein crystallization must be chosen to optimize both the siz e and solubility of the protein-detergent particle. Data for the reaction c enter suggest that crystallization occurs within a restricted range of size of the protein-detergent complex. (C) 1999 Elsevier Science B.V. All right s reserved.