A Step Toward “Fixing” The Most Important Enzyme on Earth

3926153221_3bdc08a53a_m.jpgThe world’s most abundant and most important enzyme is RuBisCo.

It’s the most abundant because it’s present in relatively large quantities in every photosynthetic organism on the planet – from microscopic cyanobacteria and phytoplankton in the oceans to the leaves of giant-sized trees in the tropics.

It’s also the most important enzyme on Earth because it catalyzes the first step in the photosynthetic conversion of CO2 into sugars (a.k.a., the Calvin cycle). Indeed, all the organic carbon in the biosphere is ultimately derived from the CO2 that RuBisCo captures from the atmosphere.

Because of its primary role in photosynthesis, the enzymatic efficiency of RuBisCo has a major impact on plant productivity. It turns out, however, that RuBisCo is a relatively inefficient enzyme and typically is the chief rate-limiting factor in agricultural productivity.

One reason RuBisCo is so inefficient is that it can react with O2 instead of CO2 much of the time. Another reason is that the current levels of atmospheric CO2 are roughly half the concentration required for RuBisCo to run at top speed. (Scientists hypothesize that the reason for these problems is that RuBisCo first evolved in cyanobacteria 3 billion years ago, when there was little atmospheric O2 and much higher levels of CO2.)

rubisco1.jpgThis is why scientists have tried to use the genetic engineering of RuBisCo to improve photosynthetic efficiency.

But a major obstacle toward this goal has been scientists’ inability to reconstitute functioning RuBisCo in vitro, that is, in a test tube.

This is mainly because the active form of RuBisCo consists of 16 proteins. (e.g., see image on right)

But a recent report in the scientific journal Nature may represent a major step toward rebuilding RuBisCo.

Reassembling RuBisCo

According to the leader of this research group at the Max Planck Institute of Biochemistry in Martinsried, Germany, Dr. Manajit Hayer-Hartl, the keys to the in vitro assembly of RuBisCo are chaperone proteins.

Chaperone proteins facilitate the correct 3D folding of newly synthesized proteins, which is critical for the optimal enzyme activity. According to Dr. Hayer-Hartl, “With 16 subunits like those of Rubisco, the risk is very high that wrong parts of the protein clump together and form useless aggregates” (1).

The next goal for this research group is to genetically modify the genes coding for the RuBisCo proteins so as to minimize binding to O2 and maximize the reaction with CO2.

“Because the modified Rubisco is predicted to absorb carbon dioxide from the atmosphere more effectively,” says Manajit Hayer-Hartl, “it would enhance crop yields and could also be interesting for climate protection.” (1)

Reference

(1) For more information, see the Press Release from the Max Planck Institute of Biochemistry and even more here.

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