Raman Spectroscopic Markers for the Xenopus Laevis Oocyte Expression System

Studying membrane protein function using Xenopus laevis oocytes has been proven to be a successful tool since its introduction more than three decades ago. Due to their great availability, large size and ease of handling, X. laevis oocytes are often superior when compared to other expression systems such as Escherichia coli or eukaryote expression systems. The Xenopus laevis oocyte expression system is able to efficiently transcribe and translate injected genetic information and to assemble, process, and target protein products. Protein characterization studies in intact whole cell injected oocytes are done using established techniques such as electrophysiology, transport assays, and calcium imaging. Recently Xenopus oocytes have been analyzed using in-vivo NMR spectroscopy, and we wondered if it would be possible to use Raman spectroscopy for non-invasive analysis of single oocytes. We present here evidence that it is possible to identify Raman bands arising from heterologous expressed membrane proteins in stage VI oocytes. This opens the possibility for integrating the Raman analysis with already established protein expression methods in order to yield complementary information about membrane protein structure and function.