title: Relation between pore sizes of protein crystals and anisotropic solute diffusivities.
abstract: The diffusion of a solute, fluorescein, into lysozyme protein crystals with different pore structures was investigated. To determine the diffusion coefficients, three-dimensional solute concentration fields acquired by confocal laser scanning microscopy (CLSM) during diffusion into the crystals were compared with the output of a time-dependent 3-D diffusion model. The diffusion process was found to be anisotropic, and the degree of anisotropy increased in the order: triclinic, tetragonal and orthorhombic crystal morphology. A linear correlation between the pore diffusion coefficients and the pore sizes was established. The maximum size of the solute, deduced from the established correlation of diffusion coefficients and pore size, was 0.73 +/- 0.06 nm, which was in the range of the average diameter of fluorescein (0.69 +/- 0.02 nm). This proves that size exclusion is the key mechanism for solute diffusion in protein crystals. Hence, the origin of solute diffusion anisotropy can be found in the packing of the protein molecules in the crystals, which determines the crystal pore organization.
authors.affiliation: Department of Biotechnology, Delft University of Technology, Julianalaan 67, 2628 BC Delft, The Netherlands.
authors.forename: Aleksandar
authors.initials: A
authors.lastname: Cvetkovic
authors.forename: Cristian
authors.initials: C
authors.lastname: Picioreanu
authors.forename: Adrie J J
authors.initials: AJ
authors.lastname: Straathof
authors.forename: Rajamani
authors.initials: R
authors.lastname: Krishna
authors.forename: Luuk A M
authors.initials: LA
authors.lastname: van der Wielen
mesh_terms: D016880:Anisotropy; D003460:Crystallization; D004058:Diffusion; D019793:Fluorescein / Q000737:chemistry*; D008958:Models, Molecular; D009113:Muramidase / Q000737:chemistry*
chemical_list: D009113:Muramidase; D019793:Fluorescein