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Publication Abstract from PubMed

Specimens below 50 kDa have generally been considered too small to be analyzed by single-particle cryo-electron microscopy (cryo-EM). The high flexibility of pure RNAs makes it difficult to obtain high-resolution structures by cryo-EM. In bacteria, riboswitches regulate sulfur metabolism through binding to the S-adenosylmethionine (SAM) ligand and offer compelling targets for new antibiotics. SAM-I, SAM-I/IV, and SAM-IV are the three most commonly found SAM riboswitches, but the structure of SAM-IV is still unknown. Here, we report the structures of apo and SAM-bound SAM-IV riboswitches (119-nt, ~40 kDa) to 3.7 A and 4.1 A resolution, respectively, using cryo-EM. The structures illustrate homologies in the ligand-binding core but distinct peripheral tertiary contacts in SAM-IV compared to SAM-I and SAM-I/IV. Our results demonstrate the feasibility of resolving small RNAs with enough detail to enable detection of their ligand-binding pockets and suggest that cryo-EM could play a role in structure-assisted drug design for RNA.

Cryo-EM structure of a 40 kDa SAM-IV riboswitch RNA at 3.7 A resolution.,Zhang K, Li S, Kappel K, Pintilie G, Su Z, Mou TC, Schmid MF, Das R, Chiu W Nat Commun. 2019 Dec 3;10(1):5511. doi: 10.1038/s41467-019-13494-7. PMID:31796736^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.