Nature chemical biology最新文献

The adenosine A_2A receptor (A_2AR) engages several G proteins, notably G_o and its cognate G_s protein. This coupling promiscuity is facilitated by a dynamic ensemble, revealed by ¹⁹F nuclear magnetic resonance imaging of A_2AR and G protein. Two transmembrane helix 6 (TM6) activation states, formerly associated with partial and full agonism, accommodate the differing volumes of G_s and G_o. While nucleotide depletion biases TM7 toward a fully active state in A_2AR–G_s, A_2AR–G_o is characterized by a dynamic inactive/intermediate fraction. Molecular dynamics simulations reveal that the NPxxY motif, a highly conserved switch, establishes a unique configuration in the A_2AR–G_o complex, failing to stabilize the helix-8 interface with G_s, and adoption of the active state. The resulting TM7 dynamics hamper G protein coupling, suggesting kinetic gating may be responsible for reduced efficacy in the noncognate G protein complex. Thus, dual TM6 activation states enable greater diversity of coupling partners while TM7 dynamics dictate coupling efficacy.

Prokaryotic clustered regularly interspaced short palindromic repeat (CRISPR)–Cas systems are highly vulnerable to phage-encoded anti-CRISPR (Acr) factors. How CRISPR–Cas systems protect themselves remains unclear. Here we uncovered a broad-spectrum anti-anti-CRISPR strategy involving a phage-derived toxic protein. Transcription of this toxin is normally repressed by the CRISPR–Cas effector but is activated to halt cell division when the effector is inhibited by any anti-CRISPR proteins or RNAs. We showed that this abortive infection-like effect efficiently expels Acr elements from bacterial population. Furthermore, we exploited this anti-anti-CRISPR mechanism to develop a screening method for specific Acr candidates for a CRISPR–Cas system and successfully identified two distinct Acr proteins that enhance the binding of CRISPR effector to nontarget DNA. Our data highlight the broad-spectrum role of CRISPR-repressed toxins in counteracting various types of Acr factors. We propose that the regulatory function of CRISPR–Cas confers host cells herd immunity against Acr-encoding genetic invaders whether they are CRISPR targeted or not.

Molecular glues are proximity-inducing small molecules that have emerged as an attractive therapeutic approach. However, developing molecular glues remains challenging, requiring innovative mechanistic strategies to stabilize neoprotein interfaces and expedite discovery. Here we unveil a trans-labeling covalent molecular glue mechanism, termed ‘template-assisted covalent modification’. We identified a new series of BRD4 molecular glue degraders that recruit CUL4^DCAF16 ligase to the second bromodomain of BRD4 (BRD4_BD2). Through comprehensive biochemical, structural and mutagenesis analyses, we elucidated how pre-existing structural complementarity between DCAF16 and BRD4_BD2 serves as a template to optimally orient the degrader for covalent modification of DCAF16_Cys58. This process stabilizes the formation of BRD4–degrader–DCAF16 ternary complex and facilitates BRD4 degradation. Supporting generalizability, we found that a subset of degraders also induces GAK–BRD4_BD2 interaction through trans-labeling of GAK. Together, our work establishes ‘template-assisted covalent modification’ as a mechanism for covalent molecular glues, which opens a new path to proximity-driven pharmacology.