title: A metastable prerequisite for the growth of lumazine synthase crystals.
abstract: Dense liquid phases, metastable with respect to a solid phase, form in solutions of proteins and small-molecule materials. They have been shown to serve as a prerequisite for the nucleation of crystals and other ordered solid phases. Here, using crystals of the protein lumazine synthase from Bacillus subtilis, which grow by the generation and spreading of layers, we demonstrate that within a range of supersaturations the only mechanism of generation of growth layers involves the association of submicrometer-size droplets of the dense liquid to the crystal surface. The dense liquid is metastable not only with respect to the crystals, but also with respect to the low-concentration solution: dynamic light scattering reveals that the droplets' lifetime is limited to several seconds, after which they decay into the low-concentration solution. The short lifetime does not allow growth to detectable dimensions so that liquid-liquid phase separation is not observed within a range of conditions broader than the one used for crystallization. If during their lifetime the droplets encounter a crystal surface, they lower their free energy not by decay, but by transformation into crystalline matter, ensuring perfect registry with the substrate. These observations illustrate two novel features of phase transformations in solutions: the existence of doubly metastable, short-lifetime dense phases and their crucial role for the growth of an ordered solid phase.
authors.affiliation: Department of Chemical Engineering, University of Houston, Houston, Texas 77204, USA.
authors.forename: Olga
authors.initials: O
authors.lastname: Gliko
authors.forename: Nikolaus
authors.initials: N
authors.lastname: Neumaier
authors.forename: Weichun
authors.initials: W
authors.lastname: Pan
authors.forename: Ilka
authors.initials: I
authors.lastname: Haase
authors.forename: Markus
authors.initials: M
authors.lastname: Fischer
authors.forename: Adelbert
authors.initials: A
authors.lastname: Bacher
authors.forename: Sevil
authors.initials: S
authors.lastname: Weinkauf
authors.forename: Peter G
authors.initials: PG
authors.lastname: Vekilov
mesh_terms: D003460:Crystallization; D004795:Enzyme Stability; D007700:Kinetics; D008027:Light; D009097:Multienzyme Complexes / Q000737:chemistry*; D012542:Scattering, Radiation; D012996:Solutions; D013816:Thermodynamics
chemical_list: D009097:Multienzyme Complexes; D012996:Solutions; C044822:6,7-dimethyl-8-ribityllumazine synthase