Abstract
The molybdenum cofactor (Moco) riboswitch is a regulatory RNA element that modulates gene expression in response to Moco binding. We employed a combination of footprinting methods, including in-line probing and selective 2’-hydroxyl acylation analyzed by primer extension (SHAPE), to analyze the structural characteristics of this riboswitch in the presence and absence of Moco-related ligands. We confirmed the riboswitch's ability to undergo a structural switch upon interaction with Moco within the Moco carrier protein (MCP) from Chlamydomonas reinhardtii. In contrast, Moco in the MCP from Volvox carteri showed no influence, emphasizing the need for a direct interaction with the RNA. In addition, we demonstrated an interaction with the sulfido Mo-MPT, a Moco derivative isolated from xanthine oxidase. We examined how the riboswitch binding is affected by the identity of the metal center, the properties of the phosphate group, and the presence of one or two MPT moieties. The structural change of the riboswitch is highly specific. While the presence of a metal-ion is essential, no difference was observed between molybdenum and tungsten. The phosphate group is involved in binding, but it remains undetermined whether it is essential or merely beneficial. These insights enhance our understanding of the Moco riboswitch.
Reichenbach, Maria