Leader in studies of how cells move proteins to present Lamport Lecture next week

Dr. Kai Simons

A fundamental problem in cell biology is how a cell specializes its plasma membrane. For example, how does a neuron make one part of its membrane into a dendrite and another part into an axon? Another way to ask the same question: how does a cell sort proteins destined for the dendrite, as opposed to the axon? Dr. Kai Simons is at the forefront of providing answers to this basic question.

Simons, director of the Cell Biology Program at the European Molecular Biology Laboratory, will give this year's Harold S. Lamport Lecture in Physiology and Biophysics. He will speak on "Lipid Rafts in Membrane Trafficking and Signaling," at 3:30 p.m., Monday, March 9, in room D-209 of the Health Sciences Center. The lecture is free and open to the public.

The approach Simons took to the question of protein sorting in the cell was to use as his model the lowly epithelial cell, whose plasma membrane helpfully contains separate areas or domains, called apical and basolateral.

He determined that sorting occurs inside the cell at a specialized part of its secretion apparatus called the trans Golgi network. First, the proteins that need sorting are put into a vesicle bound for either the apical or basolateral domains.

How do they get into the right vesicle? It turns out that the proteins contain molecular signals that direct them into the correct vesicle. This sorting mechanism is also found in all other cells, not just the epithelial cell.

Even more remarkably, the apical-basolateral distinction Simons studied has analogues in all other cells. In the neuron, the regions are actually axon and dendrite.

In his lecture next week, Simons will describe his most recent work, again in epithelial cells. These studies in protein sorting suggest a mechanism to move the proteins from the trans Golgi network at the center of the cell to either of two destinations at the cell's periphery.

The membrane of the trans Golgi network can be thought of as a "sea" of phospholipids, in which proteins and glycolipids float like icebergs.

When sorting occurs, some of the glycolipids and proteins form a raft, which becomes a vesicle destined for one domain or the other. Proteins destined for the other domain are excluded when the raft is formed.

Among Simons' many other accomplishments are work on vitamin B-12, the structure of viral membranes, and the way viruses enter animal cells. He is a member of the National Academy of Sciences in this country, in addition to many other honors.

The Lamport Lecture is supported by a gift from Mrs. Golden Lamport in honor of her late husband, who was professor of physiology and biophysics at Yale University. ¶