Investigating common luminophore in protein-metal nano-complexes

ABSTRACT Biomaterials with luminescence in the visible wavelengths are the indispensable tool of biological research today. A new class of luminescent protein material, protein-gold (Au) compounds, has attracted much attention with the versatile applications including imaging, nanomedicine, and sensing. Proteins with vastly different sizes and

functions have been discovered to yield the nearly identical luminescence. Detailed examinations across all these proteins, comparing the origin and the mechanism of the luminescence, should be desired to fully develop this emerging technological opportunity. A widely-spread interpretation of the luminophore in the protein-Au

compound is the formation of a Au nanocluster, whose size determines the property of luminescence. This model assumes proteins to have “static cage” of the same size. However, proteins are not static objects. Proteins possess inherent dynamic characters, can unfold/fold reversibly, and undergo changes among multiple

conformations, associated with protein functions. The mechanism of the luminophore formation in the protein- Au compounds may incorporate the dynamic characters of proteins and the conformation changes. Therefore, an alternative to the prevailing Au nanocluster is needed for the luminophore. We consider a new concept: The

luminophore results from binding of a Au cation to a common motif of amino acid residues in a protein, forming a coordination complex. We will elucidate this common motif by combining the spectroscopy experiments and bioinformatics analysis. The resulting knowledge is critical in identifying new luminescent protein-metal

complexes as well as in designing new luminescent peptides with broad utility in imaging, nanomedicine, and sensing.