Research shines spotlight on a key player in the dance of chromosomes

Earlier studies had established a role for CENP-E in aligning paired chromosomes. This alignment is important for ensuring that one of each pair makes its way into a different daughter cell.

CENP-E is part of a large class of proteins called kinesins. These motor proteins walk across the cell on special tightropes, called microtubules, using ATP as an energy source.

“The motion of ’normal‘ kinesin, kinesin-1, is now well known,” Selvin said. “It turns out it’s like a little person – it walks with its two feet, one in front of the other. I was interested to know whether the normal rules of how kinesin walks apply to these different kinds of kinesins.”

“In vivo studies are hampered by the presence of lots of other proteins, making it hard to study how much a single protein moves, how fast it moves and how much force it produces,” said Hasan Yardimci, a post doctoral researcher in Selvin's lab and lead author on the study.

Instead, Yardimci used a technique that allowed him to look at one molecule at a time.

The most direct way to measure how a protein moves is to watch it in real time. Using special molecular bulbs called quantum dots, which light up the protein, Yardimci was able to watch CENP-E move along its microtubule tightrope. By resolving these motions on the nanometer scale, he was able to make two key observations.

“The protein takes eight nanometer steps in a hand-over-hand fashion,” Yardimci said. The protein moved in a direction consistent with the way chromosomes move within cells, over lengths that are normally observed during cell division.

To test the kind of loads that CENP-E could withstand, Yardimci set up a tug of war between a micron-sized bead and the protein. As the protein moved, it pulled on the bead.

By measuring the force on the bead, the researchers were able to calculate how much force CENP-E could exert.

The observation that CENP-E shares several common features with kinesin-1 provides insights into its molecular workings.

“We showed that it is likely that CENP-E moves chromosomes around,” Selvin said. “That is, we showed that it is a transporter in vitro, hauling around a little bead. Now we need to do it in vivo, on chromosomes.”

The research team included Steven Rosenfeld at Columbia University.

Editor’s note: To reach Paul Selvin, call 217-244-3371; e-mail: .