Shanghai Zelixir Biotech Co., Ltd.

Thiolactomycin (1), which features a unique γ-thiolactone ring, is a promising antibiotic candidate that specifically targets bacterial type II fatty acid synthase. Despite extensive studies on its pharmacological activities, modes of action, and chemical synthesis, the enzymatic processes responsible for forming the activity-determining γ-thiolactone ring have remained largely unknown. Here, we resolve this problem by revealing that the condensation and heterocyclization (Cy) domain of the nonribosomal peptide synthetase (NRPS) TlnC (TlnC_Cy), along with the cytochrome P450 enzyme TlnA, cooperatively enable the γ-thiolactone assembly. TlnC_Cy mediates an unusual sulfurtransfer reaction to sulfurate the polyketide intermediate, generating a thiocarboxylate intermediate. Subsequently, TlnA acts as a γ-thiolactone synthase, converting the linear thiocarboxylate intermediate into 1 via a distal radical-based cyclization mechanism. These findings not only expand the functional and catalytic repertoires of NRPS Cy domains and P450 enzymes but also highlight a special enzymatic strategy for γ-thiolactone biosynthesis in nature.

The Schlafen (SLFN) family of proteins are a group of DNA/RNA processing enzymes with emerging importance in human health and disease, where their functions are implicated in a variety of immunological and anti-tumor processes. Here, we present the cryo-electron microscopy structure of full-length human SLFN14, a member with antiviral activity and linked to an inherited bleeding disorder. SLFN14 is composed of an RNase domain, a SWADL domain, and a two-lobe helicase domain. SLFN14 exhibited strong RNase activity over different substrates, and the positively charged patches at the valley of the RNase domain, which contains the thrombocytopenia-related missense mutation sites, are crucial for binding oligonucleotides. SLFN14 lacks helicase activity, which can be attributed to the inability to bind ATP and the absence of positive charges at the canonical DNA-binding site of its RecA-like folds. SLFN14 is structurally similar to SLFN11, but differs from SLFN5 in the orientation of the helicase domain. Live-cell fluorescence resonance energy transfer (FRET) assays and AlphaFold2 analysis hinted that SLFN14 may adopt multiple conformations in cells. These results provide detailed structural and biochemical features of SLFN14, and greatly expand our knowledge of the functional diversity of the SLFN family.

Macrocyclic peptides have emerged as promising drug candidates, filling the gap between small molecules and large biomolecules in drug discovery. The antiapoptotic protein myeloid cell leukemia 1 (MCL1) is crucial for numerous cancers, yet it presents challenges for selective targeting by traditional inhibitors. In this study, we identified a macrocyclic peptide, 5L1, that strongly binds to MCL1, with a dissociation constant ( K D ) of 7.1 nM. This peptide shows the potential to specifically inhibit the function of MCL1, and demonstrates effective antitumor activity against several blood tumor cell lines with the half maximal inhibitory concentration (IC 50 ) values for cell-penetrating peptide-conjugated 5L1 in the range of 0.6 to 3 μM. Structural analysis revealed that it functions similarly to molecular glue, capable of binding to two MCL1 molecules simultaneously and inducing their homodimerization. This unique mechanism of action distinguishes it from traditional small-molecule MCL1 inhibitors, underscoring the potential of macrocyclic peptides functioning as molecular glues. Moreover, it inspires the development of highly selective inhibitors targeting MCL1 and other related targets with this glue-like mechanism.