Mustafa Erbakan

Research Project

My project is related to develop Rhodobacter sphaeroides (R. sphaeroides) as an alternative bacterial platform for functional expression of medically relevant membrane proteins. Membrane proteins carry out extremely important roles for any kind of organisms including transportation of solutes and water in and out of the cells, signal transduction, cell-cell adhesion, energy generation etc. Not surprisingly, majority of the drugs on market today, directly or indirectly, target membrane proteins to regulate their activity. Despite their extreme importance, membrane proteins of known structure are quite minute compared to their soluble counterparts. Low abundance of membrane proteins in natural sources and poor performance of heterologous expression systems hinder obtaining higher amounts of membrane proteins for structural and functional studies. Membrane proteins require a lipid bioenvironment to retain their 3D structure and functionality. Expression platforms like E.coli have limited membrane surface area to accommodate heterologously expressed membrane proteins. Thus, these proteins either end up in inclusion bodies losing their 3D structure or create toxicity problems for the host. R.sphaeroides is a photosynthetic bacteria with 15 times larger membrane surface area than E.coli provided by inducible intracellular membranes (ICM) holding photosynthetic apparatus. We employ native photosynthetic promoters to synchronize membrane protein expression with ICM synthesis. Thus heterologously expressed membrane proteins target ICMs and retain their 3D structure. A variety of disease linked human membrane proteins of different membrane spanning domains such as tight junction protein, occludin and aquaporins are currently being produced at mg/L levels. The next level of the study aims the scaling up of membrane protein expression employing a photobioreactor to solve light limitations experienced by high density cultures.