One enzyme. Many roles.
Proteins within all organisms called enzymes are key to critical life processes. Scientists have studied an intriguing enzyme in sharks that regulates blood chemistry inside the gills of the sea’s top predator. In humans, the same enzyme has a similar function, aiding kidneys in regulating blood and urine functions. Yet within certain deep-sea worms, the very same enzyme has a vastly different job: to secrete acid to dissolve the bones of dead animal carcasses so that they can be consumed by the worms.
Physiologist Martín Tresguerres, an assistant professor at Scripps Institution of Oceanography at UC San Diego, has spent recent years analyzing this enzyme, called a proton pump enzyme and abbreviated as VHA, in a range of organisms, and has been fascinated by the enzyme’s varying roles among organisms.
Now, in an award-winning project, Tresguerres and colleagues including Scripps postdoctoral scholar Katie Barott have discovered VHA’s niche within coral species around the world.
In a new study published in Proceedings of the National Academy of Sciences, the Scripps scientists and their coauthors at the Centre Scientifique in Monaco looked for coral VHA and were surprised at what they found: a function vastly different than in sharks, worms, and humans.
Corals lack organs and blood such as those in sharks and humans, but they do have tissue layers that perform specific biological functions. The researchers found VHA inside coral cells that house algae that live in a mutually beneficial, or symbiotic, association within the coral. They concluded that VHA is part of a fundamental mechanism for promoting photosynthesis, the process by which organisms synthesize carbohydrates from carbon dioxide, water, and sunlight. Thanks to photosynthesis by their intricate cooperation with algae, corals get the food they need to thrive in nutrient-poor waters around the tropics.
“Plants and algae must concentrate carbon dioxide at the site of photosynthesis,” said Tresguerres. “So we believe this VHA enzyme is a mechanism by which the coral cells concentrate carbon dioxide, thus promoting and maybe controlling photosynthesis by their symbiotic algae.”
“Part of what makes this finding so exciting is that we found VHA in the same location and performing the same physiological function in two distantly related coral species,” said Barott. “This suggests that VHA’s role in promoting photosynthesis is an ancient evolutionary tactic that may be common to all symbiotic corals.”
Tresguerres likens VHA enzymes to Lego blocks, performing one role in one organism but working in a different capacity if connected differently in another organism.
“The enzyme is exactly the same, but depending on other blocks (enzymes) surrounding it, the ultimate physiological role is different,” said Tresguerres.
Such a fundamental discovery at the core of how corals live and thrive could set the stage for new ways of studying coral health in the wild.
“These results will have implications for several future studies regarding coral responses to environmental stress,” said Tresguerres, “including coral bleaching and ocean acidification, and will force us to look at results from a different perspective and reanalyze previous results and ideas.”
With the health of coral reefs declining in recent decades due to pollution, overfishing, and climate warming, the new finding could lead to new ways to aid coral recovery.
“If you want to cure a human disease such as type 2 diabetes, the first thing you need to know is how the pancreas cells work normally,” said Tresguerres. “Once you understand how they work then you can see what’s going wrong when there’s a disease. So if you want to see what happens with increased temperature or pollution or ocean acidification and how they affect corals, you first have to understand how the corals work in the first place—then you can see what goes wrong.”
Barott’s research on VHA in corals was honored with the Comparative and Evolutionary Physiology Section Scholander Award (named after Per Scholander, the late Scripps marine physiologist) at the American Physiological Society’s Intersociety meeting in San Diego in October, 2014.
With funding by the National Science Foundation, the Tresguerres Laboratory is currently working with science educators at Birch Aquarium at Scripps on an exhibit about this and other fascinating aspects of coral biology, as well as their implications for coral health in the face of human impacts such as climate change and ocean acidification. The exhibit is scheduled to open in summer 2015.
Coauthors of the paper, in addition to Tresguerres and Barott, included Alexander Venn and Sylvie Tambutté of the Centre Scientifique in Monaco and Sidney Perez of Scripps Oceanography.
The study was supported by the National Science Foundation, an Alfred P. Sloan Research Fellowship, and the Government of the Principality of Monaco.
-- Mario C. Aguilera