Posted by: woodforthetrees | March 9, 2010

Robert the Bruce and the membrane proteins

Membrane proteins are difficult

Like a spider spinning a web, obtaining membrane protein structures requires patience. Picture from Wikimedia.

Every Scottish schoolgirl and boy knows the story of King Robert the Bruce I of Scotland (1274–1329) and his many battles to free Scotland from the English. The most famous story, which even featured in our English reading books, is of Bruce hiding in a cave after being defeated in battle. He stayed there for several months feeling truly miserable. He thought about giving up and leaving Scotland.

While there, he saw a spider spinning a web at the entrance of the cave. The spider kept falling down, but climbed right back up again, time and time again, and eventually finished its web. Inspired by the spider, Bruce decided to fight again, and he told his men: “If at first you don’t succeed, try, try and try again”. Eventually he defeats the English and is crowned King of Scotland.

What has this to do with membrane proteins? At a recent meeting two stars of the protein structure world — Ray Stevens and Wayne Hendrickson — talked about their experiences working with these proteins. As membrane proteins account for about 30% of the proteins in a cell and are major drug targets, it is very important to understand them properly. Neither talked about spiders and webs, but it’s the image of Robert the Bruce that came straight to mind during their talks.

Hendrickson leads a structural genomics group, the New York Consortium on Membrane Protein Structure, and this consortium has put eight membrane proteins in the Protein Data Bank,  four of which are unique. Not much you might think for a supposedly high-throughput center with a budget of $15 million over 5 years.

But then he listed the real numbers. They have cloned 8630 targets, expressed 2669 proteins, solubilised 277 and  purified 603 proteins and solved the crystal structure of four unique targets. Quite a long way to go then to reach number 9343 on their target list.

And despite the staggering numbers involved, a reviewer apparently (I haven’t seen the reports) had the audacity to suggest that the structures they have solved must be low-hanging fruit, in other words that it must have been easy, simply because it was a structural genomics consortium involved. In my view, considering the sheer numbers involved, this comment was completely unfair.

Hendrickson threw in a useful tip though: the number one detergent for success in their hands was… beta-octylglucoside. This tidbit was received with the same attention whispering “chocolate” to nursery school is — the whole audience sat up and practically begged for more information.

Next up was Stevens who is part of several high-throughput projects that aim to increase the crystallization of membrane proteins. He works on human G-protein coupled receptors and he’s one of the very elite scientists in this field. He reeled off names of receptors whose structures his lab had solved and mentioned a couple they are finishing off. Stevens is beginning to make obtaining membrane protein structure look easy. But then he added the killer line: he’d been working on this area for 22 years.

If there is one thing that I learnt at that meeting, it’s that membrane protein structures are darned difficult. It’s a case of try, try and try again. And then again. For 8630 times or 22 years, which ever comes soonest.

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