The 22 members of the FGF family have been implicated in cell proliferation, differentiation, survival, and migration. They are required for both development and maintenance of vertebrates, demonstrating an exquisite pattern of affinities for both protein and proteoglycan receptors. FGF19, one of the most divergent human FGFs, is unique in binding solely to one receptor, FGFR4. We have used molecular replacement to solve the crystal structure of FGF19 at 1.3 Å resolution using five superimposed FGF structures as the search model. The structure shows that two novel disulfide bonds found in FGF19, one of which appears to be conserved among several of the other FGFs, stabilize extended loops. The key heparin-binding loops of FGF19 have radically different conformations and charge patterns, compared to other FGFs, correlating with the unusually low affinity of FGF19 for heparin. A model for the complex of FGF19 with FGFR4 demonstrates that unique sequences in both FGF19 and FGFR4 are key to the formation of the complex. The structure therefore offers a clear explanation for the unusual affinity of FGF19 for FGFR4 alone.

Shank is a new family of master scaffolding proteins in the postsynaptic density of eukaryotic neurons that interacts with cytosolic and membrane proteins. Shanks amplify intracellular signals involved in neurite outgrowth, cell migration and cytoskeletal organization. Shanks contain a C-terminal sterile α motif (SAM) domain. SAM domains are discrete protein modules found in diverse eukaryotes and have been shown to form polymers. The wildtype Shank 3 SAM domain is insoluble due to polymerization. To disrupt polymerization and solubilize the domain, point mutations were made at all conserved but potentially exposed sites. Four different mutants were found to be soluble and have been crystallized. Electron microscopy has shown that one N-terminal mutant forms fibers, suggesting that Shank SAM domains can polymerize at the neuron membrane. Polymerization of Shank would allow associated proteins to be clustered and thus communicate and to amplify intracellular signals. Thanks to USPHS National Research Service Award GM07185.

A new strategy is proposed for batch crystallization of proteins in solution-growth or gel-growth by using the batch method inside capillary tubes applying magnetic fields. Four proteins with differing proportions of R-helices and β-sheets and crystallized in five different crystallographic space groups are studied, allowing an analysis of the anisotropy of the diamagnetic susceptibility of the peptide bond as well as the polarity of the space groups in the presence of a strong magnetic field of 11.75 T. The crystal quality is shown to be improved by using a strong magnetic field to orient protein molecules, and gel-growth (high concentrations of agar) to control the transport phenomena as well as crystal growth. Some advantages to increase the crystal quality for crystals from marginal conditions for X-ray diffraction, and disadvantages of the use of solution-and gel-growth (low concentration of agar) in magnetic fields, and their plausible applications to high resolution X-ray crystallography are discussed.

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