How a sugar-sensing protein acts as a ‘machine’ to switch plant growth on and off

This image shows a plant protein known as KIN10 (yellow) that acts as a sensor and a switch to turn oil production off or on depending on whether it interacts with another protein (green). - Photo's: Brookhaven National Laboratory

Proteins are molecular machines, with flexible pieces and moving parts. Understanding how these parts move helps scientists unravel the function a protein plays in living things — and potentially how to change its effects.

Biochemists at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory and colleagues at DOE’s Pacific Northwest National Laboratory (PNNL) have just published a new example of how one such molecular machine works.

Their paper in the journal Science Advances describes how the moving parts of a particular plant protein control whether plants can grow and make energy-intensive products such as oil — or instead put in place a series of steps to conserve precious resources. The study focuses specifically on how the molecular machinery is regulated by a molecule that rises and falls with the level of sugar — plants’ main energy source.

The study builds on earlier work by the Brookhaven team that uncovered molecular links between sugar levels and oil production in plants. One potential goal of this research is to identify specific proteins — and parts of proteins — scientists can engineer to make plants that produce more oil for use as biofuels or other oil-based products.

This diagram shows the two pathways KIN10 and an adjacent protein, GRIK1, follow in the low- and high-sugar conditions. Low sugar allows the addition of a phosphate (P) to KIN10, which triggers a phosphorylation cascade that leads to the breakdown of enzymes involved in oil synthesis. This includes degradation of WRI1, the master-switch for oil synthesis. When sugar is abundant, however, a sugar-proxy molecule (T6P) binds to the KIN10 loop to block its interaction with GRIK1. That keeps the oil synthesis pathway open.

Unraveling molecular interactions

The team used a combination of laboratory experiments and computational modeling to zero in on how the molecule that serves as a sugar proxy binds to a “sensor kinase” known as KIN10. KIN10 is the protein that contains the moving parts that determine which biochemical pathways are on or off.

The scientists already knew that KIN10 acts as both a sugar sensor and a switch: When sugar levels are low, KIN10 interacts with another protein to set off a cascade of reactions that ultimately shut down oil production and break down energy-rich molecules like oil and starch to make energy that powers the cell. But when sugar levels are high, KIN10’s shut-down function is shut off — meaning plants can grow and make lots of oil and other products with the ab

Now that the scientists have this detailed information, how might they put it to use?

“We could potentially use our new knowledge to design KIN10 with altered binding strength for the sugar proxy to change the set point at which plants make things like oil and break things down,” said John Shanklin, chair of Brookhaven Lab’s Biology Department and leader of the research team.