Direct Line

BRET – Bioluminescence Resonance Energy Transfer

BRET (Bioluminescence Resonance Energy Transfer) is based on the fact that the energy derived from a luciferase reaction can be used to excite a fluorescent protein if the latter is in close proximity to the luciferase enzyme.

Especially in the field of G-protein coupled receptor research, BRET technology offers the opportunity to establish a homogeneous, universal and functional assay, taking advantage of the fact that ß-arrestin (which is naturally playing a role in the desensitation of the receptors) binds to the intracellular part of the activated receptor. G-protein coupled receptors, also referred to as 7-transmembrane (7TM) receptors, comprise the largest and most diverse superfamily of proteins known. To a minor part only the ligands are known.

There are several advantages of BRET over other methods: it is a non-radioactive and homogeneous technology; the ratiometric signal minimises interferences from assay conditions; and there is no auto-fluorescence coming from compounds or cell and buffer components as no light source is required.

To get some idea of how important GPCRs are in drug discovery:

  • Currently ~ 30 % of drugs are targeted against GPCRs
  • Only 5 % of the known receptors are targeted with drugs
  • To only 20 % of the rest the corresponding ligands are known

 

BRET Methods

Over the last years different BRET methods have been developed. All of them have their limitations and benefits. Various donor and acceptor pairs and their corresponding wavelengths can be found in the table below:

MethodDonorSubstrateDonor Emission [nm]AcceptorAcceptor Emission [nm]
BRET 1RLucCoelenterazine480eYFP530
BRET 2RLucDeep Blue C™395GFP510
eBRET 2RLuc8Deep Blue C™395GFP510
BRET 3FireflyLuciferin565DsRed583
QD-BRETRLuc/RLuc8Coelenterazine480QDot605

 

The original BRET method using Coelenterazine as substrate is nowadays called BRET 1. It is characterized by strong signals and long life-time.

BRET 2 in comparison has better separated donor and acceptor emission peaks. This makes BRET 2 a better choice for screening assays where high signal to noise ratios are required. A clear limitation of BRET 2 is the low light emission and the short life-time.

Enhanced BRET 2 (eBRET) – leads to approximately 5-fold better signal as in the original BRET 2 version. eBRET uses a new Renilla luciferase mutant, Rluc8.

The Firefly luciferase in BRET 3 shows lower cellular autofluorescence at the emission wavelength (565 nm) but disadavantages are weak signals and overlap between donor and acceptor emission peaks.

A brand new BRET version is the Quantum Dot-BRET (QD-BRET). The emission peaks are clearly separated which makes QD-BRET ideal for screening applications. Disadvantages are the large size of the QD molecules (1.5 - 6 nm) and the fact that genetical coding of QD-proteins is not possible. QD proteins cannot be expressed in living cells but must be added.

Literature: Bacart et al.(2008): The BRET technology and its application to screening assays, Biotechnology Journal 2008, 3, 311–324

Suitable Instruments for BRET