Dynamics of two-dimensional protein crystallization at the air/water interface: streptavidin targetted to surfaces via high-affinity binding or metal coordination

Two approaches to target proteins to monolayers at the air/water interface are compared in order to investigate the influence of the surface binding mechanism on the formation of two-dimensional (2D) protein crystals. Surface binding of the model protein streptavidin is achieved by (a) high-affinity binding to a biotinylated monolayer, and (b) coordination of surface histidines to a metal chelated IDA-lipid monolayer. Streptavidin crystallizes in both cases. The crystallization process and the crystal shapes, however, are significantly different. In a comparative study utilizing Brewster angle microscopy, we gained quantitative information regarding both the critical surface density required for the formation of 2D crystals and the compressibility of the crystalline and noncrystalline phases. Possible influences of the protein orientation, protein-protein contacts, and multiple protein populations are discussed. (C) 1997 Elsevier Science Ltd. All rights reserved.