Ultrasensitive detection of cellular protein interactions using bioluminescence resonance energy transfer quantum dot-based nanoprobes.

Sensitive detection of protein interactions is a critical step toward understanding complex cellular processes. As an alternative to fluorescence-based detection, Renilla reniformis luciferase conjugated to quantum dots results in self-illuminating bioluminescence resonance energy transfer quantum dot (BRET-Qdot) nanoprobes that emit red to near-infrared bioluminescence light. Here, we report the development of an ultrasensitive technology based on BRET-Qdot conjugates modified with streptavidin ([BRET-Qdot]-SA) to detect cell-surface protein interactions. Transfected COS7 cells expressing human cell-surface proteins were interrogated with a human Fc tagged protein of interest. Specific protein interactions were detected using a biotinylated anti-human Fc region specific antibody followed by incubation with [BRET-Qdot]-SA. The luciferase substrate coelenterazine activated bioluminescence light emission was detected with an ultra-fast and -sensitive imager. Protein interactions barely detectable by the fluorescence-based approach were readily quantified using this technology. The results demonstrate the successful application and the flexibility of the BRET-Qdot-based imaging technology to the ultrasensitive investigation of cell-surface proteins and protein-protein interactions.