title: Effects of additives on surfactant phase behavior relevant to bacteriorhodopsin crystallization.
abstract: The interactions leading to crystallization of the integral membrane protein bacteriorhodopsin solubilized in n-octyl-beta-D-glucoside were investigated. Osmotic second virial coefficients (B(22)) were measured by self-interaction chromatography using a wide range of additives and precipitants, including polyethylene glycol (PEG) and heptane-1,2,3-triol (HT). In all cases, attractive protein-detergent complex (PDC) interactions were observed near the surfactant cloud point temperature, and there is a correlation between the surfactant cloud point temperatures and PDC B(22) values. Light scattering, isothermal titration calorimetry, and tensiometry reveal that although the underlying reasons for the patterns of interaction may be different for various combinations of precipitants and additives, surfactant phase behavior plays an important role in promoting crystallization. In most cases, solution conditions that led to crystallization fell within a similar range of slightly negative B(22) values, suggesting that weakly attractive interactions are important as they are for soluble proteins. However, the sensitivity of the cloud point temperatures and resultant coexistence curves varied significantly as a function of precipitant type, which suggests that different types of forces are involved in driving phase separation depending on the precipitant used.
authors.affiliation: Center for Molecular and Engineering Thermodynamics, Department of Chemical Engineering, University of Delaware, Newark, Delaware 19716, USA. bergerbw@mail.med.upenn.edu
authors.forename: Bryan W
authors.initials: BW
authors.lastname: Berger
authors.forename: Colleen M
authors.initials: CM
authors.lastname: Gendron
authors.forename: Abraham M
authors.initials: AM
authors.lastname: Lenhoff
authors.forename: Eric W
authors.initials: EW
authors.lastname: Kaler
mesh_terms: D000473:Alkanes / Q000494:pharmacology; D001436:Bacteriorhodopsins / Q000737:chemistry* / Q000187:drug effects; D003460:Crystallization / Q000379:methods*; D005233:Fatty Alcohols / Q000494:pharmacology; D019617:Halobacterium salinarum / Q000737:chemistry; D008565:Membrane Proteins / Q000737:chemistry / Q000187:drug effects; D011092:Polyethylene Glycols / Q000494:pharmacology; D012492:Salts / Q000494:pharmacology; D013501:Surface-Active Agents / Q000737:chemistry / Q000378:metabolism*; D013696:Temperature
chemical_list: D000473:Alkanes; D005233:Fatty Alcohols; D008565:Membrane Proteins; D012492:Salts; D013501:Surface-Active Agents; C068115:heptane-1,2,3-triol; D011092:Polyethylene Glycols; D001436:Bacteriorhodopsins