High-resolution yeast actin structures indicate the molecular mechanism of actin filament stiffening by cations.

Actin filament assembly and the regulation of its mechanical properties are fundamental processes essential for eukaryotic cell function. Residue E167 in vertebrate actins forms an inter-subunit salt bridge with residue K61 of the adjacent subunit. Saccharomyces cerevisiae actin filaments are more flexible than vertebrate filaments and have an alanine at this position (A167).

Dynamic and asymmetric fluctuations in the microtubule wall captured by high-resolution cryoelectron microscopy.

Microtubules are tubular polymers with essential roles in numerous cellular activities. Structures of microtubules have been captured at increasing resolution by cryo-EM. However, dynamic properties of the microtubule are key to its function, and this behavior has proved difficult to characterize at a structural level due to limitations in existing structure determination methods.

Structures of cofilin-induced structural changes reveal local and asymmetric perturbations of actin filaments.

Members of the cofilin/ADF family of proteins sever actin filaments, increasing the number of filament ends available for polymerization or depolymerization. Cofilin binds actin filaments with positive cooperativity, forming clusters of contiguously bound cofilin along the filament lattice. Filament severing occurs preferentially at boundaries between bare and cofilin-decorated (cofilactin) segments and is biased at 1 side of a cluster.

Structural basis of the filamin A actin-binding domain interaction with F-actin.

Actin-cross-linking proteins assemble actin filaments into higher-order structures essential for orchestrating cell shape, adhesion, and motility. Missense mutations in the tandem calponin homology domains of their actin-binding domains (ABDs) underlie numerous genetic diseases, but a molecular understanding of these pathologies is hampered by the lack of high-resolution structures of any actin-cross-linking protein bound to F-actin. Here, taking advantage of a high-affinity, disease-associated mutant of the human filamin A (FLNa) ABD, we combine cryo-electron microscopy and functional studies to reveal at near-atomic resolution how the first calponin homology domain (CH1) and residues immediately N-terminal to it engage actin.

The actin filament twist changes abruptly at boundaries between bare and cofilin-decorated segments.

Cofilin/ADF proteins are actin-remodeling proteins, essential for actin disassembly in various cellular processes, including cell division, intracellular transport, and motility. Cofilins bind actin filaments cooperatively and sever them preferentially at boundaries between bare and cofilin-decorated (cofilactin) segments. The cooperative binding to actin has been proposed to originate from conformational changes that propagate allosterically from clusters of bound cofilin to bare actin segments.

High-resolution cryo-EM structures of actin-bound myosin states reveal the mechanism of myosin force sensing.

Myosins adjust their power outputs in response to mechanical loads in an isoform-dependent manner, resulting in their ability to dynamically adapt to a range of motile challenges. Here, we reveal the structural basis for force-sensing based on near-atomic resolution structures of one rigor and two ADP-bound states of myosin-IB (myo1b) bound to actin, determined by cryo-electron microscopy. The two ADP-bound states are separated by a 25° rotation of the lever.

Phosphomimetic S3D cofilin binds but only weakly severs actin filaments.

Many biological processes, including cell division, growth, and motility, rely on rapid remodeling of the actin cytoskeleton and on actin filament severing by the regulatory protein cofilin. Phosphorylation of vertebrate cofilin at Ser-3 regulates both actin binding and severing. Substitution of serine with aspartate at position 3 (S3D) is widely used to mimic cofilin phosphorylation in cells and The S3D substitution weakens cofilin binding to filaments, and it is presumed that subsequent reduction in cofilin occupancy inhibits filament severing, but this hypothesis has remained untested.

Characterization of a weakly expressed KIR2DL1 variant reveals a novel upstream promoter that controls KIR expression.

Members of the human KIR (killer cell immunoglobulin-like receptor) class I major histocompatibility complex receptor gene family contain multiple promoters that determine the variegated expression of KIR on natural killer cells. In order to identify novel genetic alterations associated with decreased KIR expression, a group of donors was characterized for KIR gene content, transcripts and protein expression. An individual with a single copy of the KIR2DL1 gene but a very low level of gene expression was identified.

Identification of a KIR antisense lncRNA expressed by progenitor cells.

Human NK cells express cell surface class I MHC receptors (killer cell immunoglobulin-like receptor, KIR) in a probabilistic manner. Previous studies have shown that a distal promoter acts in conjunction with a proximal bidirectional promoter to control the selective activation of KIR genes. We report here the presence of an intron 2 promoter in several KIR genes that produce a spliced antisense transcript.