Deciphering the mechanism(s) of -sheet mediated self-assembly is essential for understanding amyloid fibril formation and for the fabrication of polypeptide materials. Herein, we report a simple peptidomimetic that self-assembles into polymorphic -sheet quaternary structures including protofilaments, filaments, fibrils, and ribbons that are reminiscent of the highly ordered structures displayed by the amyloidogenic peptides A , calcitonin, and amylin. The distribution of quaternary structures can be controlled by and in some cases specified by manipulating the pH, buffer composition, and the ionic strength. The ability to control -sheet-mediated assembly takes advantage of quaternary structure dependent pK a perturbations. Biophysical methods including analytical ultracentrifugation studies as well as far-UV circular dichroism and FT-IR spectroscopy demonstrate that linked secondary and quaternary structural changes mediate peptidomimetic self-assembly. Electron and atomic force microscopy reveal that peptidomimetic assembly involves numerous quaternary structural intermediates that appear to self-assemble in a convergent fashion affording quaternary structures of increasing complexity. The ability to control the assembly pathway(s) and the final quaternary structure(s) afforded should prove to be particularly useful in deciphering the quaternary structural requirements for amyloid fibril formation and for the construction of noncovalent macromolecular structures.The self-assembly of peptides and proteins into noncovalent -sheet rich quaternary structures, including fibrils, has attracted the attention of numerous laboratories owing to their association with neurodegenerative disease and their interesting structures. [1][2][3][4][5][6][7][8][9][10] In both amyloid and prion diseases a normally soluble protein or proteolytic fragment undergoes a conformational change either prior to, or coincident with, its self-assembly into -sheet rich fibrils, implicated as the causative agent in numerous neurodegenerative diseases by genetic linkage. [11][12][13][14][15][16][17][18][19] Previous studies on amyloid fibril assembly establish the presence of quaternary structural intermediates, which appear to undergo convergent assembly into intermediates of increasing complexity until amyloid fibrils are ultimately afforded. [20][21][22][23][24][25][26][27][28] The differing quaternary structures observed could explain the strains char- ‡ Laboratory of Molecular Biology. (3) Yamada, N.; Katsuhiko, A.; Naito, M.; Matsubara, K.; Koyama, E. J. Am. Chem. Soc. 1998, 120, 12192-12199. (4) Janek, K.; Behlke, J.; Zipper, J.; Fabian, H.; Georgalis, Y.; Beyemmann, M.; Bienert, M.; Krause, E.

. Biochemical analyses of recombinant Ace and Cna A domains supported the modeling data in that the secondary structures were similar as determined by CD spectroscopy and both proteins bound at multiple sites in type I collagen with micromolar affinities, but with different apparent kinetics. We conclude that Ace is a collagen-binding MSCRAMM on enterococci and is structurally and functionally related to the staphylococcal Cna protein.

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A method for the preparation and characterization of bioinorganic conjugates made with highly luminescent semiconductor CdSe-ZnS core-shell quantum dots (QDs) and antibodies for use in fluoroimmunoassays is presented. The conjugation strategy employs two routes: 1. Use of an engineered molecular adaptor protein, attached to the QDs via electrostatic/hydrophobic self-assembly, to link the inorganic fluorophore with antibodies, and 2. use of avidin, also electrostatically selfassembled onto the nanocrystal surface, which allows QD conjugation to biotinylated antibodies via avidin-biotin binding scheme. With this approach, the average number of antibodies conjugated to a single QD can be varied. In addition, we have developed a simple purification strategy based on mixed composition conjugates of the molecular adaptor and a second "inert" two-domain fusion protein that allows the use of affinity chromatography. QD/adaptor-antibody conjugates were successfully employed in fluoroimmunoassays for the detection of small molecule analytes, 2,4,6-trinitrobenzene (TNB) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). We also demonstrate the use of QD/avidin-antibody conjugates for fluoroimmunoassays using a model protein system.Introduction Colloidal semiconductor nanocrystals (quantum dots, QDs) are spherical particles in a size regime dominated by strong quantum confinement of the charge carriers. This confinement lifts the degeneracy of the carrier states within the conduction and valence bands, and increases the effective band gap energy significantly with decreasing particle size, resulting in size dependence of several properties, such as absorption and photoluminescence (PL) spectra [1][2][3]. Colloidal QDs with surfaces ligated with a variety of functional capping groups can be dispersed in organic solvents, and water-compatible QDs have been prepared either directly by using aqueous-compatible surface caps, or indirectly by embedding the particles in micron-size beads and functionalizing the surface of the beads with ligands to make them water compatible [4][5][6][7][8]. Luminescent colloidal QDs have the potential to circumvent some of the functional limitations encountered by organic dyes in biotechnological applications. Organic fluorophores have characteristics that limit their effectiveness for certain applications. These limitations include narrow excitation bands and broad emission bands with red spectral tails, and many organic dyes exhibit low resistance to photodegradation [9]. In contrast, CdSe-ZnS core-shell QDs exhibit narrow PL with full width at half-maximum (FWHM) of 30-45 nm that spans the visible spectrum, and they have broad absorp-