Bending forces and nucleotide state jointly regulate F-actin structure.

ATP-hydrolysis-coupled actin polymerization is a fundamental mechanism of cellular force generation1-3. In turn, force4,5 and actin filament (F-actin) nucleotide state6 regulate actin dynamics by tuning F-actin's engagement of actin-binding proteins through mechanisms that are unclear. Here we show that the nucleotide state of actin modulates F-actin structural transitions evoked by bending forces. Cryo-electron microscopy structures of ADP-F-actin and ADP-Pi-F-actin with sufficient resolution to visualize bound solvent reveal intersubunit interfaces bridged by water molecules that could mediate filament lattice flexibility. Despite extensive ordered solvent differences in the nucleotide cleft, these structures feature nearly identical lattices and essentially indistinguishable protein backbone conformations that are unlikely to be discriminable by actin-binding proteins. We next introduce a machine-learning-enabled pipeline for reconstructing bent filaments, enabling us to visualize both continuous structural variability and side-chain-level detail. Bent F-actin structures reveal rearrangements at intersubunit interfaces characterized by substantial alterations of helical twist and deformations in individual protomers, transitions that are distinct in ADP-F-actin and ADP-Pi-F-actin. This suggests that phosphate rigidifies actin subunits to alter the bending structural landscape of F-actin. As bending forces evoke nucleotide-state dependent conformational transitions of sufficient magnitude to be detected by actin-binding proteins, we propose that actin nucleotide state can serve as a co-regulator of F-actin mechanical regulation.

Prevalence of Sleep CALM nocturia factors in a male veteran population.

INTRODUCTION: Nocturia is a complex and multifactorial condition, associated with several genitourinary abnormalities as well as a host of conditions beyond the urinary tract, and thus often poses a significant diagnostic challenge in real-world practice. Sleep Disorders, Comorbidities, Actions, Lower Urinary Tract Dysfunction, and Medications, the so-called "Sleep C.A.L.M." factors, are five common causes of nocturia requiring judicious evaluation according to current consensus guidelines. This study aims to assess the prevalence of the Sleep C.A.L.M. factors in a nocturia clinical population. METHODS: Retrospective analysis of frequency-volume charts from men with ≥2 nocturnal voids as well as concurrent demographic, clinical, and medical history data to identify patients with each of the Sleep C.A.L.M. FACTORS: Comorbidities and medications were classified as a single group. RESULTS: A total of 213 subjects met the criteria for inclusion (median age 68.0 [63.5-75.5] years). The prevalence of 1) sleep disorders, 2) comorbidities and/or medication use, 3) actions (i.e., modifiable behaviors/lifestyle factors), and 4) lower urinary tract dysfunction was 31%, 31%, 19%, and 41%, respectively. Among included participants, 73% were found to have at least 1 Sleep C.A.L.M. factor, and 33% had multiple Sleep C.A.L.M. FACTORS: Results were similar upon stratification by age and nocturnal polyuria status. CONCLUSIONS: The Sleep C.A.L.M. factors are highly common among nocturia patients in the clinical urology setting. Although many of these factors are strongly associated with advanced age in community-based nocturia study samples, they appear common even among younger men in a nocturia patient population; the differential effect of age and individual Sleep C.A.L.M. factors on nocturia pathophysiology requires further investigation.

Metallothionein-3 attenuates the effect of Cu2+ ions on actin filaments.

Metallothionein 3 (MT-3) is a cysteine-rich metal-binding protein that is expressed in the mammalian central nervous system and kidney. Various reports have posited a role for MT-3 in regulating the actin cytoskeleton by promoting the assembly of actin filaments. We generated purified, recombinant mouse MT-3 of known metal compositions, either with zinc (Zn), lead (Pb), or copper/zinc (Cu/Zn) bound. None of these forms of MT-3 accelerated actin filament polymerization in vitro, either with or without the actin binding protein profilin. Furthermore, using a co-sedimentation assay, we did not observe Zn-bound MT-3 in complex with actin filaments. Cu2+ ions on their own induced rapid actin polymerization, an effect that we attribute to filament fragmentation. This effect of Cu2+ is reversed by adding either EGTA or Zn-bound MT-3, indicating that either molecule can chelate Cu2+ from actin. Altogether, our data indicate that purified recombinant MT-3 does not directly bind actin but it does attenuate the Cu-induced fragmentation of actin filaments.

Alterations to the broad-spectrum formin inhibitor SMIFH2 modulate potency but not specificity.

SMIFH2 is a small molecule inhibitor of the formin family of cytoskeletal regulators that was originally identified in a screen for suppression of actin polymerization induced by the mouse formin Diaphanous 1 (mDia1). Despite widespread use of this compound, it is unknown whether SMIFH2 inhibits all human formins. Additionally, the nature of protein/inhibitor interactions remains elusive. We assayed SMIFH2 against human formins representing six of the seven mammalian classes and found inhibitory activity against all formins tested. We synthesized a panel of SMIFH2 derivatives and found that, while many alterations disrupt SMIFH2 activity, substitution of an electron-donating methoxy group in place of the bromine along with halogenation of the furan ring increases potency by approximately five-fold. Similar to SMIFH2, the active derivatives are also pan-inhibitors for the formins tested. This result suggests that while potency can be improved, the goal of distinguishing between highly conserved FH2 domains may not be achievable using the SMIFH2 scaffold.