1 research outputs found
Optimizing Protein Coordination to Quantum Dots with Designer Peptidyl Linkers
Semiconductor quantum dots (QDs) demonstrate select optical
properties
that make them of particular use in biological imaging and biosensing.
Controlled attachment of biomolecules such as proteins to the QD surface
is thus critically necessary for development of these functional nanobiomaterials.
QD surface coatings such as poly(ethylene glycol) impart colloidal
stability to the QDs, making them usable in physiological environments,
but can impede attachment of proteins due to steric interactions.
While this problem is being partially addressed through the development
of more compact QD ligands, here we present an alternative and complementary
approach to this issue by engineering rigid peptidyl linkers that
can be appended onto almost all expressed proteins. The linkers are
specifically designed to extend a terminal polyhistidine sequence
out from the globular protein structure and penetrate the QD ligand
coating to enhance binding by metal-affinity driven coordination.
α-Helical linkers of two lengths terminating in either a single
or triple hexahistidine motif were fused onto a single-domain antibody;
these were then self-assembled onto QDs to create a model immunosensor
system targeted against the biothreat agent ricin. We utilized this
system to systematically evaluate the peptidyl linker design in functional
assays using QDs stabilized with four different types of coating ligands
including poly(ethylene glycol). We show that increased linker length,
but surprisingly not added histidines, can improve protein to QD attachment
and sensor performance despite the surface ligand size with both custom
and commercial QD preparations. Implications for these findings on
the development of QD-based biosensors are discussed