Structural basis for Y2 receptor-mediated neuropeptide Y and peptide YY signaling

Neuropeptide Y (NPY) and its receptors are expressed in various human tissues including the brain where they regulate appetite and emotion. Upon NPY stimulation, the neuropeptide Y1 and Y2 receptors (Y₁R and Y₂R, respectively) activate G_I signaling, but their physiological responses to food intake are different. In addition, deletion of the two N-terminal amino acids of peptide YY (PYY(3-36)), the endogenous form found in circulation, can stimulate Y₂R but not Y₁R, suggesting that Y₁R and Y₂R may have distinct ligand-binding modes. Here, we report the cryo-electron microscopy structures of the PYY(3-36)‒Y₂R‒G_i and NPY‒Y₂R‒G_i complexes. Using cell-based assays, molecular dynamics simulations, and structural analysis, we revealed the molecular basis of the exclusive binding of PYY(3-36) to Y₂R. Furthermore, we demonstrated that Y₂R favors G protein signaling over β-arrestin signaling upon activation, whereas Y₁R does not show a preference between these two pathways.

Recent progress in the structural study of ion channels as insecticide targets

Ion channels, many expressed in insect neural and muscular systems, have drawn huge attention as primary targets of insecticides. With the recent technical breakthroughs in structural biology, especially in cryo-electron microscopy (cryo-EM), many new high-resolution structures of ion channel targets, apo or in complex with insecticides, have been solved, shedding light on the molecular mechanism of action of the insecticides and resistance mutations. These structures also provide accurate templates for structure-based insecticide screening and rational design. This review summarizes the recent progress in the structural studies of 5 ion channel families: the ryanodine receptor (RyR), the nicotinic acetylcholine receptor (nAChR), the voltage-gated sodium channel (VGSC), the transient receptor potential (TRP) channel, and the ligand-gated chloride channel (LGCC). We address the selectivity of the channel-targeting insecticides by examining the conservation of key coordinating residues revealed by the structures. The possible resistance mechanisms are proposed based on the locations of the identified resistance mutations on the 3D structures of the target channels and their impacts on the binding of insecticides. Finally, we discuss how to develop "green" insecticides with a novel mode of action based on these high-resolution structures to overcome the resistance.

Bivalent recognition of histone marks by BARD1

BARD1 directs BRCA1 to DNA damage sites to facilitate homology recombination. Zhou and colleagues have now determined the cryo-electron microscopy (cryo-EM) structure of BARD1 bound to a nucleosome core particle with two marks: H2AK15ub and H4K20me0. The structure illustrates how bivalent recognition of both marks mediates highly specified recruitment of the BARD1-BRCA1 complex.

Molecular Insights Into the Gating Kinetics of the Cardiac hERG Channel, Illuminated by Structure and Molecular Dynamics

The rapidly activating delayed rectifier K⁺ current generated by the cardiac hERG potassium channel encoded by KCNH2 is the most important reserve current for cardiac repolarization. The unique inward rectification characteristics of the hERG channel depend on the gating regulation, which involves crucial structural domains and key single amino acid residues in the full-length hERG channel. Identifying critical molecules involved in the regulation of gating kinetics for the hERG channel requires high-resolution structures and molecular dynamics simulation models. Based on the latest progress in hERG structure and molecular dynamics simulation research, summarizing the molecules involved in the changes in the channel state helps to elucidate the unique gating characteristics of the channel and the reason for its high affinity to cardiotoxic drugs. In this review, we aim to summarize the significant advances in understanding the voltage gating regulation of the hERG channel based on its structure obtained from cryo-electron microscopy and computer simulations, which reveal the critical roles of several specific structural domains and amino acid residues.

Structural insight into BRCA1-BARD1 complex recruitment to damaged chromatin

The BRCA1-BARD1 complex directs the DNA double-strand break (DSB) repair pathway choice to error-free homologous recombination (HR) during the S-G2 stages. Targeting BRCA1-BARD1 to DSB-proximal sites requires BARD1-mediated nucleosome interaction and histone mark recognition. Here, we report the cryo-EM structure of BARD1 bound to a ubiquitinated nucleosome core particle (NCP^Ub) at 3.1 Å resolution and illustrate how BARD1 simultaneously recognizes the DNA damage-induced mark H2AK15ub and DNA replication-associated mark H4K20me0 on the nucleosome. In vitro and in vivo analyses reveal that the BARD1-NCP^Ub complex is stabilized by BARD1-nucleosome interaction, BARD1-ubiquitin interaction, and BARD1 ARD domain-BARD1 BRCT domain interaction, and abrogating these interactions is detrimental to HR activity. We further identify multiple disease-causing BARD1 mutations that disrupt BARD1-NCP^Ub interactions and hence impair HR. Together, this study elucidates the mechanism of BRCA1-BARD1 complex recruitment and retention by DSB-flanking nucleosomes and sheds important light on cancer therapeutic avenues.

Cryo-EM structures elucidate neutralizing mechanisms of anti-chikungunya human monoclonal antibodies with therapeutic activity

Chikungunya virus (CHIKV) is a mosquito-transmitted alphavirus that causes severe acute and chronic disease in humans. Although highly inhibitory murine and human monoclonal antibodies (mAbs) have been generated, the structural basis of their neutralizing activity remains poorly characterized. Here, we determined the cryo-EM structures of chikungunya virus-like particles complexed with antibody fragments (Fab) of two highly protective human mAbs, 4J21 and 5M16, that block virus fusion with host membranes. Both mAbs bind primarily to sites within the A and B domains, as well as to the B domain's β-ribbon connector of the viral glycoprotein E2. The footprints of these antibodies on the viral surface were consistent with results from loss-of-binding studies using an alanine scanning mutagenesis-based epitope mapping approach. The Fab fragments stabilized the position of the B domain relative to the virus, particularly for the complex with 5M16. This finding is consistent with a mechanism of neutralization in which anti-CHIKV mAbs that bridge the A and B domains impede movement of the B domain away from the underlying fusion loop on the E1 glycoprotein and therefore block the requisite pH-dependent fusion of viral and host membranes.