Functional expression of rat alpha 2B-adrenoceptor in Escherichia coli

Strategies for the cloning and expression of membrane proteins

Despite the determination of thousands of high-resolution structures of soluble proteins, many features of integral membrane proteins render them difficult targets for the structural biologist. Among these, the most important challenge is in expressing sufficient quantities of active protein to support downstream purification and structure determination efforts. Over 190 unique membrane protein structures have now been solved, and noticeable trends in successful expression strategies are beginning to emerge. A number of groups have also explored high-throughput (HTP) methods for membrane protein expression, with varying degrees of success. Here we review the current state of expressing membrane proteins for functional and structural studies. We first survey successful methods that have already yielded levels of membrane protein expression sufficient for structure determination. HTP methods are also examined since these aim to explore large numbers of targets and can predict reasonable starting points for many membrane proteins. Since HTP techniques may fail, particularly for certain classes of eukaryotic targets, detailed strategies for the expression of two prominent classes of eukaryotic protein families, G-protein-coupled receptors and ion channels, are also summarized.

Determination on functional basis of presynaptic alpha 2-adrenoceptor subtypes in guinea-pig duodenum

The effects of several alpha 2-adrenoceptor agonists and antagonists were examined on the cholinergic twitch contractions evoked by electrical field stimulation of guinea-pig duodenum. Oxymetazoline, xylazine, noradrenaline, alpha-methyl-noradrenaline or medetomidine (0.01-30 microM) were nearly equieffective in inhibiting duodenal twitch responses. The effects of xylazine were competitively counteracted by antagonists tested (0.03-10 microM) with the following order of potency: RX 821002 = idazoxan > rauwolscine = yohimbine = BRL 44408 >> prazosin = ARC 239 = BRL 41992. According to the current classification, it is suggested that alpha 2-heteroadrenoceptors involved in the modulation of duodenal cholinergic neurotransmission belong to the alpha ZD subtype.