A simple and inexpensive nanoliter‐volume dispenser for highly viscous materials used in membrane protein crystallization

Macromolecular crystallization trials involve the testing of large numbers of chemical and environmental conditions. For each, a certain amount of protein and precipitant is required. In the case of membrane proteins, detergent and lipids must be included in the screen, which adds to the number of trials performed. With rare exceptions, membrane proteins come at a premium. Thus, there is a pressing need to scale down the screening process so as to make most efficient use of these scarce materials. Lipids and detergents can also be very expensive and miniaturization is of benefit here too. Recently, a glass‐plate system for crystallizing membrane proteins by the in meso method was introduced [Cherezov & Caffrey (2003). J. Appl. Cryst. 36 , 1372–1377; Caffrey (2003). J. Struct. Biol. 142 , 108–132]. The protocol calls for the handling of small volumes of lipidic/protein dispersions that are extraordinarily viscous. A positive‐displacement syringe‐based tool was implemented for the preparation and dispensing of these refractory mixtures. However, the device, assembled from commercial parts, operated with microliter‐sized samples and was not as economical as it could be in terms of delivered volumes. To effect further miniaturization, and thus conservation of materials, the dispenser has been modified in a way that facilitates accurate and precise repetitive delivery by hand of nanoliter volumes of liquids and of highly viscous dispersions. Here the modifications, which can be made simply and inexpensively to commercially available parts, along with the performance characteristics of the newly configured dispenser, are described