Enzymes that catalyse remarkable Diels–Alder-like [4+2] cyclizationshave been previously implicated in the biosynthesis of spirotetronate andspirotetramate antibiotics. Biosynthesis of the polyether antibiotic tetronasinis not expected to require such steps, yet the tetronasin gene cluster encodesenzymes Tsn11 and Tsn15, which are homologous to authentic [4+2] cyclases. Here,we show that deletion of Tsn11 led to accumulation of a late-stageintermediate, in which the two central rings of tetronasin and four of itstwelve asymmetric centres remain unformed. In vitro reconstitution showed thatTsn11 catalyses an apparent inverse-electron-demand hetero-Diels–Alder-like [4+2] cyclization ofthis species to form an unexpected oxadecalin compound that is then rearrangedby Tsn15 to form tetronasin. To gain structural and mechanistic insight intothe activity of Tsn15, the crystal structure of a Tsn15-substrate complex hasbeen solved at 1.7 A resolution.

Conventional CRISPR/Cas genetic manipulation has beenprofitably applied to the genus Streptomyces, the most prolific bacterial producers of antibiotics. However, its reliance on DNA double-strand break (DSB) formation leads to unacceptably low yields of desiredrecombinants. We have adapted for Streptomyces recently-introduced cytidinebaseeditors (CBEs) and adenine base editors (ABEs) which enable targeted C-to-T or A-to-G nucleotide substitutions, respectively, by passing DSB and the need for arepair template. We report successful genome editing in Streptomyces at frequencies of around 50% using defectiveCas9-guided base editors and up to 100% by using nicked Cas9-guided baseeditors. Furthermore, we demonstrate the multiplex genome editing potential of thenicked Cas9-guided base editor BE3 by programmed mutation of nine target genes simultaneously. Use of the high-fidelity version of BE3 (HF-BE3) essentially improvedediting specificity. Collectively, this work provides a powerful new tool for genomeediting in Streptomyces.

作为曾经治疗细菌感染的一线临床药物，氨基糖苷类抗生素在人类与病源微生物的抗争中作出了不可磨灭的巨大贡献，也成就了这一类抗生素的辉煌。虽然，伴随着其耳毒性和肾毒性等毒副作用，以及日益严重的耐药性的严峻挑战，但借助现代科学技术的发展和认知水平的提高，氨基糖苷类抗生素许多不曾被了解的新的生物活性也正不断地丰富和拓展着它新的潜能，使之依然成为人类医药宝库中不可或缺的重要一员。基于此，本文从分子遗传学、生物化学及结构生物学角度对常见的天然和化学半合成氨基糖苷抗生素生物合成的研究进展进行简要的概述。

As a kind of first-line antibiotics clinically used for treating bacterial infections, aminoglycosides have greatly contributed to human health against pathogenic microbes and its brilliance has also been realized. Despite its side effects such as ototoxicity and nephrotoxicity and growing challenges of drug resistance, aminoglycosides are still an indispensable and important member of the treasure house of medicine, since many new bioactivities of aminoglycosides that have not been known are constantly enriching and expanding their new potential with the development of science and technology and understanding. In this review, the research progress in genetics, chemical biology, and structural biology of natural and semi-synthesized aminoglycoside are summarized and briefly discussed.