Sterol biosynthesis in the echinoderm Asterias rubens

Area of Science:

• Biochemistry
• Marine Biology
• Echinoderm Physiology

Background:

• Sterol biosynthesis is a fundamental metabolic pathway in many organisms.
• Echinoderms, such as starfish, possess unique lipid compositions that warrant investigation into their metabolic capabilities.
• Understanding sterol origins in marine invertebrates is crucial for ecological and biochemical studies.

Purpose of the Study:

• To investigate the de novo sterol biosynthesis capabilities of the echinoderm Asterias rubens.
• To identify the sterol intermediates and final products synthesized from mevalonic acid in A. rubens.
• To determine the origin of various sterol classes found in A. rubens, distinguishing between endogenous synthesis and dietary uptake.

Main Methods:

• Administration of [2(-14)C]mevalonic acid to the echinoderm Asterias rubens.
• Analysis of the non-saponifiable lipid fraction to identify and quantify labelled sterol compounds.
• Radiolabeling studies on isolated tissues to pinpoint sites of sterol synthesis.

Main Results:

• Effective incorporation of [2(-14)C]mevalonic acid into squalene, lanosterol, and various methylated sterol intermediates in A. rubens.
• Demonstration that the major sterol, 5alpha-cholest-7-en-3beta-ol, is synthesized de novo by A. rubens.
• Lack of evidence for de novo synthesis of C28-C29 sterols and cyclopropane sterols, suggesting dietary origin for these compounds.

Conclusions:

• Asterias rubens possesses the enzymatic machinery for de novo sterol biosynthesis, utilizing mevalonic acid as a precursor.
• The study elucidates the pathway for sterol synthesis in this echinoderm, identifying key intermediates.
• Complex sterols not synthesized de novo are likely acquired exogenously, highlighting a mixotrophic sterol acquisition strategy in A. rubens.