Transport of Delight

I spent most of last weekend and all of yesterday finalising a chapter I had been asked to contribute to an upcoming monograph on human serum albumin. Monograph is a fancy word for book in academia. And academia is a fancy word for the people who work in universities and research institutes and consider themselves smart.

Yesterday I was polishing the text of my latest draft and assembling the figures. My group has been working with albumin for over fourteen years now and I am pretty familiar with it. The familiarity makes it difficult to come at the subject afresh but I like playing around with the graphics software to see if I can come up with a new angle. In doing so I made the figure below, which is a variant of one that I prepared for my book chapter.

Human serum albumin - loaded with ligands

Familiarity, it is well known, also breeds contempt or, at the very least, a certain laziness. With albumin it becomes easy to overlook the truly remarkable features of the molecule, but working at my figures yesterday was a salutary reminder of the fecundity of nature at the molecular level.

Albumin is a protein molecule made in your liver and then released into your bloodstream and the fluids surrounding the cells of your major organs. It is made in large amounts — you have about 200 grammes of the stuff — and does a tour of duty lasting about a month. In that time the molecule circulates in the body helping to transport a range of smaller molecules, some of which, like fatty acids, the body depends on for nutrition and growth; others are toxins like hemin and bilirubin, byproducts of cellular damage that need to be carted off to the liver for disposal.

The protein is extraordinary in the way that its structure has adapted to grab hold of such a variety of different compounds. I can’t think of another molecule like it. The picture above is an aggregate of many years of work, most of it done in my lab. The image is unrealistic in that is shows albumin binding to many of its different cargos at the same time — fatty acids in dark grey, bilirubin in pink, hemin in light grey (just behind the bilirubin) and four molecules of the hormone thyroxine in yellow. But it does give a good idea of the astounding transport capacity of the protein.

Albumin is a thing of wonder and, tough though it was to grind through the writing and re-writing of my chapter (not to mention the years of laboratory slog that went into the work), the beauty of the image reminds me what a delightful privilege it is to do science.



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