Biological complexity: 3 plant enzymes produce lignin (Introduction)

by David Turell , Tuesday, May 01, 2018, 01:19 (2399 days ago) @ David Turell

The complex process is now understood:

https://phys.org/news/2018-04-molecular-machinery-cell-wall-components.html

"Plants are among the most effective energy convertors on Earth. They capture solar energy and convert it to carbon-based compounds that are used for energy and also to build up essential plant components, including the cell walls that surround every single plant cell. In a new biochemical genetics study at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory, scientists reveal new details of the molecular machinery that helps channel carbon into a key cell-wall component.

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"The study, published in Nature Plants, reports how two proteins embedded on membranes within plant cells serve as a scaffold to organize three key enzymes that specifically channel carbon into the synthesis of a cell-wall polymer called lignin.

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"The three enzymes establish the structural characteristics of biochemical building blocks known as monolignols, which link up to form lignin. Scientists previously thought that these enzymes were associated with one another and served as the anchor sites for organizing monolignol synthesis.

"'We started this project to study the interactions of these three enzymes in detail," said Brookhaven biochemist and project leader Chang-Jun Liu. "We discovered that even though the three enzymes are located near one another on a membrane known as the endoplasmic reticulum, they don't interact directly. Instead, two separate proteins interact with all three enzymes."

"The separate proteins are "membrane steroid binding proteins" (MSBPs) embedded in the endoplasmic reticulum—a cell's interior "highway" of membranes lined with the molecular machines that make proteins and transport those products within or out of cells.

"'These membrane-bound proteins serve as a scaffold to organize and stabilize the three enzymes into a type of molecular machinery that controls the metabolic pathway channeling carbon specifically into building lignin precursors," Liu said.

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"'Those observations strongly suggested that the MSBPs organize the monolignol biosynthesis enzymes into a multimeric protein complex or enzymatic cluster," Liu said.
"With that type of organization, the three enzymes could be located close to one another without necessarily having direct interactions," he added. Such an arrangement would help drive lignin synthesis by keeping the enzymes and their common cofactor near one another at high enough concentrations to effectively transfer the carbon substrates and electrons needed for efficient chemical reactions to take place.

"To test the role of the MSBPs, the scientists created plant lines in which the genes for these proteins were suppressed. While those plants could still make the three monolignol synthesis enzymes, they ended up with significantly less lignin.

"In addition, such suppression did not affect the formation of another closely related class of chemicals whose synthesis requires one of the three monolignol synthesis enzymes.
These data convinced the scientists that MSBP-mediated enzyme organization specifically facilitates lignin formation. "

Comment: Lignin gives plants strength to stand tall like trees. The efficiency of this arrangement reeks of design, and the combination of three giant complex enzymes cannot have happened by chance. Each enzyme has a specific function so this mimics a factory production line, which, of course, is designed.