Translocation Pathway-Dependent Assembly of Streptavidin- and Antibody-Binding Filamentous Virus-Like Particles

Design and Characterization of a New pVII Combinatorial Phage Display Peptide Library for Protease Substrate Mining Using Factor VII Activating Protease (FSAP) as Model

We describe a novel, easy and efficient combinatorial phage display peptide substrate-mining method to map the substrate specificity of proteases. The peptide library is displayed on the pVII capsid of the M13 bacteriophage, which renders pIII necessary for infectivity and efficient retrieval, in an unmodified state. As capture module, the 3XFLAG was chosen due to its very high binding efficiency to anti-FLAG mAbs and its independency of any post-translational modification. This library was tested with Factor-VII activating protease (WT-FSAP) and its single-nucleotide polymorphism variant Marburg-I (MI)-FSAP. The WT-FSAP results confirmed the previously reported Arg/Lys centered FSAP cleavage site consensus as dominant, as well as reinforcing MI-FSAP as a loss-of-function mutant. Surprisingly, rare substrate clones devoid of basic amino acids were also identified. Indeed one of these peptides was cleaved as free peptide, thus suggesting a broader range of WT-FSAP substrates than previously anticipated.

Multiplex immunoassays using virus-tethered gold microspheres by DC impedance-based flow cytometry

Bead-based multiplex immunoassays for common use require enhanced sensitivity and effective prevention of non-specific adsorption, as well as miniaturization of the detection device. In this work, we have implemented virus-tethered gold microspheres for multiplex immunoassay applications, employing a DC impedance-based flow cytometer as a detection element. The advantages of virus-tethered gold microspheres, including excellent prevention of non-specific adsorption, are extended to signal enhancement arising from the large quantity of antibody loading on each virion, and to flexible movement of filamentous virus. Individual virus-tethered beads generate their own DC impedance and fluorescence signals, which are simultaneously detected by a chip-based microfluidic flow cytometer. This system successfully realized multiplex immunoassays involving four biomarkers: cardiac troponin I (cTnI), prostate specific antigen (PSA), creatine kinase MB (CK-MB), and myoglobin in undiluted human sera, elevating sensitivity by up to 5.7-fold compared to the beads without virus. Constructive integration between filamentous virus-tethered Au-layered microspheres and use of a microfluidic cytometer suggests a promising strategy for competitive multiplex immunoassay development based on suspension arrays.