Structural biology of integral membrane proteins - From methods to molecular mechanisms

Abstract

Membrane proteins are vital components in the cell and crucial for the proliferation of all living organisms. Unfortunately our collective knowledge of structures of membrane proteins is very limited, as compared to the information available on soluble proteins. This is to a large extent due to the outstanding challenge of working with membrane proteins and the relatively high cost associated with determining a membrane protein structure.  Therefore, the establishment of efficient methods and means for the production and crystallization of membrane proteins is urgently needed. The two methods explored in this thesis  are aimed to achieve rapid optimization of expression and purification conditions of membrane proteins, thereby allowing for the rapid production of more suitable samples for crystallization trials. Despite the challenges in membrane protein structure determination two structures are presented in the thesis: The first structure determined is of the CorA magnesium transporter from Thermotoga maritima will be the focus of this thesis. The CorA revealed a pentameric protein in a closed state. The presence of two regulatory metal binding sites is suggested, as well as a putative magnesium ion bound in the ion conductive pathway. The second structure is of the human enzyme LTC4-synthase, which catalyzes the pivotal step in eicosanoid synthesis by the conjugation of glutathione to LTA4, a reactive epoxide-containing derivative from arachidonic acid. The products of this step, the so-called cysteinyl leukotrienes are potent inflammatory mediators making this enzyme a potential drug target. The structure reveals a charged binding pocket for a horseshoe-shaped glutathione, and a hydrophobic binding pocket for a lipophilic LTA4 molecule. Based on the structure a key residue for catalysis has been identified, Arg 104, which is proposed to play a critical role in activating the thiol group of glutathione for the nucleophilic attack on LTA4