An alternative pathway for cysteine production

Cysteine is a crucial amino acid involved in protein synthesis and cellular metabolism. It is well established that cysteine is produced through a metabolic process known as the transsulfuration pathway, which is dependent on an enzyme called cystathionine β-synthase. As this enzyme is absent in corals of the genus Acropora, it had been supposed that Acropora relies on symbiosis with dinoflagellates to produce cysteine.

The existence of the alternative metabolic route, named the O-succinylserine pathway, suggests A. loripes has the capacity for cysteine production without relying on symbionts. The pathway involves the action of two proteins, Cys2 and Cys1a. The researchers confirmed the involvement of the two proteins in cysteine production in living A. loripes samples.

“We were really surprised to find this alternative pathway for cysteine biosynthesis in A. loripes, as it was previously only identified in fungi and we thought animals could only synthesize cysteine through the transsulfuration pathway,” says Octavio Salazar of the Red Sea Research Center, King Abdullah University of Science and Technology (KAUST), Saudi Arabia. 

Salazar adds that by performing a phylogenetic analysis, it was surprising to find that the alternative pathway is present throughout the animal kingdom except for vertebrates, arthropods and nematodes. Since so many studies are based on model organisms belonging to the groups of nematodes and mammals, the researchers caution against generalizing findings across biological systems.

“I think it is a good reminder to everyone working with less studied organisms — that we still have many things to discover about life and that whenever we study something, we should approach it with an open mind and be aware that sometimes our current knowledge may lead to preconceptions that could be misleading,” he says.

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