hopanoïdes

Hopanoids are a class of pentacyclic triterpenoids that are structurally similar to cholesterol. They are widely distributed in bacteria and archaea, but are generally absent in eukaryotes, with some exceptions. Hopanoids play important roles in membrane structure and function in microorganisms. They are thought to stabilize the lipid bilayer, reduce its fluidity, and influence the activity of membrane-bound proteins. The most common hopanoid is hopene, but a variety of substituted hopanoids exist, differing in the presence and position of methyl groups, hydroxyl groups, and other modifications.

The biosynthesis of hopanoids begins with the cyclization of squalene, a precursor also involved in cholesterol synthesis. This cyclization leads to the formation of hopanoids through a series of enzymatic steps. The study of hopanoids is significant in several fields. In geology and paleontology, fossilized hopanoids, known as hopanes, are used as biomarkers to infer the presence of microbial life in ancient sediments and petroleum. Their presence can indicate the type of microorganisms that were present and the conditions under which they lived. In microbiology, understanding hopanoid function helps to elucidate the adaptations of microorganisms to different environments and their interactions with host organisms. Furthermore, some hopanoids have been investigated for potential pharmacological applications due to their biological activities.