Sperm production needs more proteins (Image: Clifford Barnes, University of Ulster/SPL)

Congratulations testicles, you make more unique proteins than any other tissue in the body.

The proteins in our cells and tissues are responsible for everything from repair and maintenance to the production of signalling chemicals. You might expect that the brain, being our most sophisticated organ, would produce the widest array of proteins. But while the brain hosts 318 unique proteins that we know of, testicles are home to 999.

It is one of the surprising messages from the latest, most comprehensive version of the Human Protein Atlas “proteome” – an inventory of all the proteins produced in the human body. Launched this week on proteinatlas.org, the atlas represents a decade of work in 13 laboratories, led by Mathias Uhlén of the Royal Institute of Technology in Stockholm, Sweden.


Many of the proteins found in testicles are involved in the type of cell division that produces sperm, says Uhlén. “What’s going on in the testes is unique, as sperm must survive with half the chromosomes and outside the human body.”

He says egg-making ovaries may well have a similar number, but eggs are made inside fetuses, so he will not be testing this theory.

Protein malfunctions

Knowing which proteins are made in each organ in a healthy individual should make it easier for researchers to zero in on the proteins that malfunction in disease, and so better design new drugs and treatments.

“It’s all very well knowing all our genes but at the end of the day, all human disease and biology stem from the proteins – the building blocks of humans,” says Uhlén. “What we’ve produced is like a Gray’s Anatomy for proteins.”

The Human Genome Project revealed 10 years ago that humans have 20,000 genes that code for proteins – from those that build our bodies and organs to those we depend on for all the cell processes that keep us alive. The atlas reveals for the first time where most of these proteins are made and what they are doing in our bodies.

As well as the surprise about testes proteins, the project has made some other intriguing findings. For instance, almost half our genes – 8847 – are switched on in all our cells, performing all the biochemical donkey work on which all life depends, such as producing energy, reading DNA and turning it into proteins. “Cars like Ferraris and Volkswagens may look very different, but the basic components of both are roughly the same, and that’s how it is with organs and proteins,” says Uhlén.

In contrast, 2355 of our proteins are uniquely produced in specific organs, meaning that these proteins must play a key role in determining the dramatic physical differences between organs as diverse as skin and the brain.

The project was launched in 2005 and tissues for the atlas were donated by 360 healthy people.